Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery of the present application comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. 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 particles having different primary particle sizes, the particles comprising a lithium-containing transition metal phosphate material. The average molar ratio of Mn in particles distributed in a medium-particle-size region is higher than the average molar ratio in particles distributed in a small-particle-size region and the average molar ratio in particles distributed in a large-particle-size region, respectively, wherein the molar ratio of Mn refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe. The secondary battery of the present application has good powder compaction density, good gram capacity, and excellent storage performance.

Description

Secondary batteries and electrical devices

[0001] Cross-references

[0002] This application references Chinese Patent Application No. 202411034832.5, 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] Secondary batteries have advantages such as high energy density, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in the consumer electronics field.

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

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

[0007] The first aspect of this application provides a secondary battery, the secondary battery including a positive electrode, a negative electrode and an electrolyte, 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;

[0008] The positive electrode film layer includes particles with different primary particle sizes. The particles include the lithium-containing transition metal phosphate material. The average molar percentage of Mn in the particles distributed in the medium particle size region is higher than the average molar percentage of Mn in the particles distributed in the small particle size region and the average molar percentage of Mn in the particles distributed in the large particle size region. The molar percentage of Mn refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0009] By employing a gradation design of large-diameter, medium-diameter, and small-diameter particles, the filling and stacking of the positive electrode active material particles become more uniform and compact, improving the compaction density of the positive electrode sheet. The redox potential of manganese ions is higher than that of iron ions, resulting in a higher voltage plateau for lithium manganese iron phosphate 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. Small-diameter particles have a larger specific surface area and significantly increased surface activity, making them more susceptible to contact with the electrolyte and subsequent side reactions, exacerbating manganese dissolution and affecting the battery's storage performance. The secondary battery of this application, by controlling the average molar ratio of Mn in the small-diameter particles of the positive electrode film to be lower than that in the medium-diameter particles, helps reduce the degree of side reactions between the small-diameter particles and the electrolyte, as well as the rate of manganese dissolution, thereby improving the storage performance of the secondary battery. Furthermore, 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 in the large-particle region increases the migration path of lithium ions within the particle, leading to increased particle discharge polarization and decreased specific capacity. This application addresses this by controlling the average molar percentage of Mn in the large-particle region to be lower than that in the medium-particle region, which helps alleviate discharge polarization in the large-particle region, resulting in a battery with superior specific capacity. Through appropriate gradation design and the design of the average molar percentage of Mn in particles of different primary particle sizes, the secondary battery of this application exhibits good compaction density, as well as good storage performance and good specific capacity.

[0010] In any embodiment, the molar percentage of Mn in the particles distributed in the medium particle size region is higher than that in the particles distributed in the small particle size region and the particles distributed in the large particle size region.

[0011] When the molar percentage of Mn in the particles of each particle size region is as described above, the average molar percentage satisfies the design of the average molar percentage of Mn in this application. The secondary battery of this application has good compaction density, as well as good storage performance and good specific capacity.

[0012] In any embodiment, the molar percentage of Mn in the particles distributed in the small-diameter region varies arbitrarily with the increase of the primary particle size; and / or,

[0013] The molar percentage of Mn in the particles distributed in the medium particle size region varies arbitrarily with the increase of the primary particle size.

[0014] The molar percentage of Mn in the particles distributed in the large particle size region varies arbitrarily with the increase of the primary particle size.

[0015] Depending on the primary particle size of the lithium-containing transition metal phosphate material added during the preparation of the positive electrode active material, the molar ratio of Mn in the particles distributed in the small-particle-size region, medium-particle-size region, and large-particle-size region of the positive electrode film layer of this application exhibits various different trends as the primary particle size changes.

[0016] In any embodiment, the molar percentage of Mn in the particles first increases and then decreases as the primary particle size of the particles increases.

[0017] In any embodiment, the molar percentage of Mn in the particles increases first and then decreases continuously with the increase of the primary particle size.

[0018] In any embodiment, the molar percentage of Mn in the particles distributed in the small-diameter region increases with increasing primary particle size; and / or,

[0019] The molar percentage of Mn in the particles distributed in the medium-sized region first increases and then decreases with increasing primary particle size; and / or,

[0020] The molar percentage of Mn in the particles distributed in the large-size region decreases as the primary particle size increases.

[0021] In any embodiment, the molar percentage of Mn in the particles exhibits a trend of constant-increase-constant-decrease-constant-constant as the primary particle size increases.

[0022] In any embodiment, the molar percentage of Mn in the particles distributed in the small-diameter region remains constant and then increases with the increase of the primary particle size; and / or,

[0023] The molar percentage of Mn in the particles distributed in the medium-sized region shows a trend of increasing-remaining constant-decreasing with increasing primary particle size; and / or,

[0024] The molar percentage of Mn in the particles distributed in the large-size region first decreases and then remains constant as the primary particle size increases.

[0025] When the molar percentage of Mn in each particle size region increases with the primary particle size as described above, the average molar percentage satisfies the design of the average molar percentage of Mn in each particle size region of this application. The secondary battery of this application has good compaction density, as well as good storage performance and good specific capacity.

[0026] In any embodiment, the molar percentage of Mn in the particles changes continuously with the increase of the primary particle size.

[0027] In any embodiment, the molar percentage of Mn in the particles changes discontinuously with the increase of the primary particle size.

[0028] In any embodiment, the primary particle size of the particles distributed in the small particle size region is less than or equal to 180 nm and greater than or equal to 50 nm, the primary particle size of the particles distributed in the medium particle size region is greater than 180 nm and less than 900 nm, and the primary particle size of the particles distributed in the large particle size region is greater than or equal to 900 nm and less than or equal to 5 μm.

[0029] When the primary particle size of the particles in the small-diameter region, medium-diameter region, and large-diameter region is within the above-mentioned range, it is beneficial to further improve the compaction density.

[0030] In any embodiment, in the positive electrode film layer, based on the total number of moles of Mn in the lithium-containing transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small particle size region is less than or equal to 12% and greater than or equal to 0%.

[0031] In any embodiment, in the positive electrode film layer, based on the total number of moles of Mn in the lithium-containing transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small-diameter region is less than or equal to 8%.

[0032] In any embodiment, in the positive electrode film layer, based on the total number of moles of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small particle size region is less than or equal to 6%.

[0033] Further controlling the molar ratio of Mn in the small-diameter region of the particles within a suitable range is beneficial to further improving the storage performance of the secondary battery of this application.

[0034] In any embodiment, in the positive electrode film layer, based on the total number of moles of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small particle size region is greater than or equal to 0.02%.

[0035] In any embodiment, in the positive electrode film layer, based on the total number of moles of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small particle size region is greater than or equal to 0.2%.

[0036] Small-diameter particles have better electrical conductivity. Compared to small-diameter particles that do not contain Mn, particles containing a certain amount of Mn help to improve the voltage plateau of the secondary voltage while also having better specific capacitance.

[0037] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the large particle size region to the average molar percentage of Mn in the particles distributed in the medium particle size region is less than or equal to 0.8 and greater than or equal to 0.

[0038] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the large particle size region to the average molar percentage of Mn in the particles distributed in the medium particle size region is less than or equal to 0.5.

[0039] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the large particle size region to the average molar percentage of Mn in the particles distributed in the medium particle size region is greater than or equal to 0.0003.

[0040] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the large particle size region to the average molar percentage of Mn in the particles distributed in the medium particle size region is greater than or equal to 0.002.

[0041] Further controlling the ratio of the average molar percentage of Mn in the large-size region particles to the average molar percentage of Mn in the medium-size region particles within a certain range is beneficial to further improve the specific capacity of the secondary battery of this application, while also having good volumetric energy density and storage performance.

[0042] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the small-diameter region to the average molar percentage of Mn in the particles distributed in the medium-diameter region is less than or equal to 0.8 and greater than or equal to 0.

[0043] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the small-diameter region to the average molar percentage of Mn in the particles distributed in the medium-diameter region is less than or equal to 0.4.

[0044] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the small-diameter region to the average molar percentage of Mn in the particles distributed in the medium-diameter region is greater than or equal to 0.0003.

[0045] In any embodiment, the ratio of the average molar percentage of Mn in the particles distributed in the small-diameter region to the average molar percentage of Mn in the particles distributed in the medium-diameter region is greater than or equal to 0.002.

[0046] By further controlling the ratio of the average molar percentage of Mn in the small-diameter region to the average molar percentage of Mn in the small-diameter region, the secondary battery of this application has good volumetric energy density and further improved storage performance.

[0047] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the small-diameter region is less than or equal to 6:4 and greater than or equal to 0.

[0048] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the small-diameter region is less than or equal to 4:6.

[0049] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the small-diameter region is greater than or equal to 0.02:9.98.

[0050] When the average manganese-iron molar ratio of particles in the small-diameter region is within a suitable range, it is beneficial to further reduce the side reactions between phosphate particles and electrolyte in the small-diameter region and the degree of manganese dissolution. As a result, the battery has a good volumetric energy density and its storage performance is further improved.

[0051] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the medium particle size region is greater than or equal to 4:6 and less than or equal to 9:1.

[0052] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the medium particle size region is greater than or equal to 5:5 and less than or equal to 9:1.

[0053] Medium-sized 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 medium-sized particles within a suitable range is beneficial for increasing the total molar amount of manganese in the lithium transition metal phosphate material 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.

[0054] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the large particle size region is less than or equal to 6:4 and greater than or equal to 0.

[0055] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the large-size region is less than or equal to 5:5.

[0056] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the large-size region is greater than or equal to 0.2:9.8.

[0057] In any embodiment, the average manganese-iron molar ratio of the particles distributed in the large-size region is greater than or equal to 1:9.

[0058] When the average manganese-iron molar ratio of the large-diameter particles is within a suitable range, it can alleviate the discharge polarization of the large-diameter particles, improve the specific capacity, and the battery can have a good volumetric energy density while further improving its storage performance.

[0059] In any embodiment, the average manganese-iron molar ratio of the particles in the positive electrode film layer is greater than or equal to 2:8 and less than or equal to 9:1.

[0060] In any embodiment, the average manganese-iron molar ratio of the particles in the positive electrode film layer is greater than or equal to 2:8 and less than or equal to 6:4.

[0061] When the average manganese-iron molar ratio of the particles in the positive electrode film is within a suitable range, lithium-containing transition metal phosphate materials 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.

[0062] In any embodiment, based on the total area of ​​the particles in the positive electrode film layer, the area percentage of the particles distributed in the small-diameter region is greater than 0% and less than or equal to 30%; and / or,

[0063] The area of ​​the particles distributed in the medium-sized region is greater than or equal to 20% and less than 100%; and / or,

[0064] The area of ​​the particles distributed in the large-size region is greater than 0% and less than or equal to 80%.

[0065] In any embodiment, based on the total area of ​​the particles in the positive electrode film, the area percentage of the particles distributed in the small-diameter region is greater than or equal to 5% and less than or equal to 15%; and / or,

[0066] The area of ​​the particles distributed in the medium-sized region is greater than or equal to 40% and less than or equal to 85%; and / or,

[0067] The area of ​​the particles distributed in the large-size region is greater than or equal to 5% and less than or equal to 40%.

[0068] When the area ratio of medium-sized particles is within a suitable range, the battery exhibits superior volumetric energy density and storage performance. When the area ratio of small-sized particles is within a suitable range, the battery exhibits superior compaction density, volumetric energy density, and storage performance. When the area ratio of large-sized particles is within a suitable range, lithium-containing transition metal phosphate materials exhibit superior powder compaction density, specific capacity, and storage life, resulting in superior volumetric energy density and storage performance.

[0069] In any embodiment, the particles distributed in the small-diameter region 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, 3.5 ≤ n1 ≤ 4, 0 ≤ a1 ≤ 0.1, 0 ≤ b1 ≤ 0.1, 0 ≤ c1 ≤ 0.1, 0 ≤ d1 ≤ 0.1; and / or,

[0070] The particles distributed in the medium-sized region 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, 3.5 ≤ n2 ≤ 4, 0 ≤ a2 ≤ 0.1, 0 ≤ b2 ≤ 0.1, 0 ≤ c2 ≤ 0.1, 0 ≤ d2 ≤ 0.1; and / or,

[0071] The particles distributed in the medium-sized region 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, 3.5≤n3≤4, 0≤a3≤0.1, 0≤b3≤0.1, 0≤c3≤0.1, and 0≤d3≤0.1.

[0072] 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 material, 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 .

[0073] The higher the powder compaction density, the higher the mass of powder material per unit volume. When the powder compaction density of the positive electrode active material 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.

[0074] 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.

[0075] In any embodiment, the single-sided coating weight of the positive electrode sheet is 300 mg / 1540 mm. 2 -580mg / 1540mm 2 .

[0076] In any embodiment, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0077] A second aspect of this application provides an electrical device comprising a secondary battery of the first party. Attached Figure Description

[0078] Figure 1 is a longitudinal cross-sectional schematic diagram of the positive electrode sheet according to an embodiment of this application;

[0079] Figure 2 is a graph showing the molar ratio of Mn in the particles of Example 1 versus the primary particle size.

[0080] Figure 3 is a graph showing the molar ratio of Mn in the particles of Example 2 versus the primary particle size.

[0081] Figure 4 is a schematic diagram of the statistical distinction rules of primary particles in the transmission electron microscope image of particles in this application;

[0082] Figure 5 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0083] Figure 6 is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 5;

[0084] Figure 7 is a schematic diagram of a battery module according to an embodiment of this application;

[0085] Figure 8 is a schematic diagram of a battery pack according to an embodiment of this application;

[0086] Figure 9 is an exploded view of the battery pack of one embodiment of this application shown in Figure 8;

[0087] Figure 10 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0088] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0089] 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.

[0090] 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.

[0091] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0092] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0093] 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.

[0094] 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.

[0095] 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).

[0096] The cathode active material is one of the decisive factors in the performance of secondary batteries. Currently, common cathode active materials mainly include lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, and lithium iron phosphate. Each material has its advantages and disadvantages. For example, lithium cobalt oxide has high energy density and voltage plateau, but its cost is high and its safety is poor; lithium manganese oxide has lower cost and better safety, but its energy density and voltage plateau are lower; nickel-cobalt-manganese ternary materials combine the advantages of the former two, but their cost is still high. Lithium iron phosphate has advantages such as low cost, high safety, and long lifespan, which can better meet the requirements of the new energy vehicle market for high safety and low cost of lithium-ion batteries. However, lithium iron phosphate also has some disadvantages, such as low compaction density and low discharge capacity, which limit its application in high-energy-density batteries. Lithium manganese iron phosphate, as a new material for the further development of lithium iron phosphate, combines the advantages of manganese and iron, and has two voltage plateaus at 4.1V and 3.4V respectively, which can provide a certain plateau capacity and is expected to improve the shortcomings of lithium iron phosphate. However, in current research and application, lithium manganese iron phosphate still suffers from the problem of low compaction density. Therefore, how to improve the compaction density of lithium manganese iron phosphate while maintaining good storage performance and specific capacity has become a key research focus.

[0097] [Rechargeable Battery]

[0098] Based on this, this application provides a secondary battery, which includes a positive electrode, a negative electrode and an electrolyte, 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.

[0099] The positive electrode film layer includes particles with different primary particle sizes. The particles include lithium transition metal phosphate materials. The average molar percentage of Mn in the particles distributed in the medium particle size region is higher than the average molar percentage of Mn in the particles distributed in the small particle size region and the average molar percentage of Mn in the particles distributed in the large particle size region. The molar percentage of Mn refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0100] As shown in Figure 1, the positive electrode 10 includes a positive current collector 110 and a positive electrode film 120 disposed on at least one side of the positive current collector. The positive electrode film includes particles 1201 in a small-diameter region, particles 1202 in a medium-diameter region, and particles 1203 in a large-diameter region.

[0101] In this paper, the term "primary particle size" refers to the particle size of a primary particle.

[0102] 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 4 is a schematic diagram of the statistical distinction rules for primary particles in a transmission electron microscope (TEM) image. Figure 4-a is the original TEM image, Figure 4-b is the software-recognized image, and Figure 4-c is an example of software and / or manual identification of independent, adhered, and stacked particles in Figure 4-a. Particles 1 and 2 are distinguishable independent particles, designated as primary particles 1 and 2, respectively. Particles 3 and 4 in Figure 4-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 4-d is another example of software and / or manual identification of the stacked particles in Figure 4-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.

[0103] The average molar percentage of Mn in the particles can be tested using methods and equipment known in the art, for example as follows: disassemble the battery to obtain the positive electrode sheet, peel off the positive electrode film layer of the positive electrode sheet, thoroughly wash the positive electrode film layer with acetone to remove binders and dispersants in the positive electrode film layer, filter and dry 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). Simultaneously, EDS point scanning can be used to test the Mn and Fe content of each effective particle in the transmission electron microscope (TEM) image, thereby calculating the molar percentage of Mn (X) in each effective particle (the molar percentage of Mn refers to the content of the number of moles of Mn relative to the total number of moles of Mn and Fe). The test point is the middle part of the transmission surface of each primary particle. TEM and EDS tests are performed multiple times within different test intervals, testing the cross-sectional area S, primary particle size d, and molar percentage of Mn X of at least 500 effective particles. The tested effective particles are then numbered from smallest to largest primary particle size as 1, 2, 3, 4, 5…n, with a total of n particles. The formula for calculating the average molar percentage of Mn in the particles is:

[0104] Where Xi represents the molar percentage of Mn in particle number i, and Si represents the cross-sectional area of ​​particle number i.

[0105] Particles numbered 1, 2, 3, 4, 5…n are divided into three regions—A, B, and C—as their primary particle size increases. Specifically, if the average molar percentage of Mn in particles distributed in region B is higher than the average molar percentages of Mn in regions A and C, then region B is considered the medium-sized region, region A the small-sized region, and region C the large-sized region. More specifically, the m-th particle is the largest primary particle size in region A, the (m+1)-th particle is the smallest primary particle size in region B, the (k-1)-th particle is the largest primary particle size in region B, and the k-th particle is the smallest primary particle size in region C. Therefore, particles 1 to m are considered small-sized particles, particles (m+1) to (k-1)-sized particles are medium-sized particles, and particles k to n-sized particles are large-sized particles.

[0106] The formula for calculating the average molar percentage of Mn in the small-diameter region is as follows:

[0107] The formula for calculating the average molar percentage of Mn in particles of medium size is as follows:

[0108] The formula for calculating the average molar percentage of Mn in particles with large particle size is as follows:

[0109] Where Xi represents the molar percentage of Mn in particle number i, and Si represents the cross-sectional area of ​​particle number i.

[0110] By employing a gradation design of large-diameter, medium-diameter, and small-diameter particles, the filling and stacking of the positive electrode active material particles become more uniform and compact, improving the compaction density of the positive electrode sheet. The redox potential of manganese ions is higher than that of iron ions, resulting in a higher voltage plateau for lithium manganese iron phosphate 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. Small-diameter particles have a larger specific surface area and significantly increased surface activity, making them more susceptible to contact with the electrolyte and subsequent side reactions, exacerbating manganese dissolution and affecting the battery's storage performance. The secondary battery of this application, by controlling the average molar ratio of Mn in the small-diameter particles of the positive electrode film to be lower than that in the medium-diameter particles, helps reduce the degree of side reactions between the small-diameter particles and the electrolyte, as well as the rate of manganese dissolution, thereby improving the storage performance of the secondary battery. Furthermore, 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 in the large-particle region increases the migration path of lithium ions within the particle, leading to increased particle discharge polarization and decreased specific capacity. This application addresses this by controlling the average molar percentage of Mn in the large-particle region to be lower than that in the medium-particle region, which helps alleviate discharge polarization in the large-particle region, resulting in a battery with superior specific capacity. Through appropriate gradation design and the design of the average molar percentage of Mn in particles of different primary particle sizes, the secondary battery of this application exhibits good compaction density, as well as good storage performance and good specific capacity.

[0111] In some embodiments, the molar percentage of Mn in particles distributed in the medium-diameter region is higher than that in particles distributed in the small-diameter region and in particles distributed in the large-diameter region.

[0112] The molar ratio of Mn in particles of different size regions can be characterized by a curve graph. Specifically, the primary particle size d and the molar ratio X of Mn for each effective particle were determined using the aforementioned testing method. The parameters of each effective particle were plotted with the primary particle size as the x-axis and the molar ratio of Mn as the y-axis. A curve was obtained through statistical fitting. The curve shows that the molar ratio of Mn in particles distributed in the medium particle size region is higher than that in particles distributed in the small particle size region and particles distributed in the large particle size region. When multiple particles exist within a given particle size, and the molar ratio of Mn differs among different particles, the molar ratio X of Mn for that particle size is the average of the molar ratios of Mn for different particles of the same particle size.

[0113] In some implementations, when there are multiple particles of the same primary particle size, the molar percentage of Mn in the particles distributed in the medium particle size region is the average of the molar percentages of Mn in the multiple particles of that primary particle size. When there is only one particle of the same primary particle size, the molar percentage of Mn in the particles distributed in the medium particle size region is the molar percentage of Mn in that single particle. The molar percentage of Mn in the particles distributed in the small particle size region and the molar percentage of Mn in the particles distributed in the large particle size region have a similar understanding to that of the molar percentage of Mn in the particles distributed in the medium particle size region.

[0114] When the molar percentage of Mn in particles of each particle size region is as described above, the average molar percentage satisfies the design of the average molar percentage of Mn in this application. The secondary battery of this application has good compaction density, as well as good storage performance and good specific capacity.

[0115] In some implementations, the molar percentage of Mn in particles distributed in the small-diameter region varies arbitrarily with the increase of the primary particle size.

[0116] In some implementations, the molar percentage of Mn in particles distributed in the medium-diameter region varies arbitrarily with the increase of the primary particle size.

[0117] In some implementations, the molar percentage of Mn in particles distributed in the large-diameter region varies arbitrarily with the increase of the primary particle size.

[0118] In some embodiments, the molar percentage of Mn in particles distributed in the small-diameter region can independently exhibit an increasing trend, a decreasing trend, a wave-like trend, a fixed value trend, or a combination of trends as the primary particle size increases; the molar percentage of Mn in particles distributed in the medium-diameter region can independently exhibit an increasing trend, a decreasing trend, a wave-like trend, a fixed value trend, or a combination of trends as the primary particle size increases; and the molar percentage of Mn in particles distributed in the medium-diameter region can independently exhibit an increasing trend, a decreasing trend, a wave-like trend, a fixed value trend, or a combination of trends as the primary particle size increases.

[0119] Depending on the primary particle size of the lithium-containing transition metal phosphate material added during the preparation of the positive electrode active material, the molar proportion of Mn in the particles distributed in the small-particle-size region, medium-particle-size region, and large-particle-size region of the positive electrode film layer of this application shows a variety of different trends as the primary particle size changes.

[0120] In some implementations, the molar percentage of Mn in the particles first increases and then decreases with the increase of the primary particle size.

[0121] In some implementations, the molar percentage of Mn in the particles increases first and then decreases continuously with the increase of the primary particle size.

[0122] In some embodiments, the molar percentage of Mn in particles distributed in the small-diameter region increases with increasing primary particle size; and / or,

[0123] The molar percentage of Mn in particles distributed in the medium-sized region first increases and then decreases with increasing primary particle size; and / or,

[0124] The molar percentage of Mn in particles distributed in the large-size region decreases as the primary particle size increases.

[0125] Figure 3 shows a fitted curve showing that the molar percentage of Mn in particles initially increases and then decreases with increasing primary particle size. Specifically, the molar percentage of Mn in particles distributed in the small-size region increases with increasing primary particle size. During the increase in primary particle size, there may be a partial plateau period, during which the molar percentage of Mn in particles in the small-size region remains constant. The molar percentage of Mn in particles distributed in the medium-size region initially increases and then decreases with increasing primary particle size. During the increase in primary particle size, there may be a partial plateau period, during which the molar percentage of Mn in particles in the medium-size region remains constant. The molar percentage of Mn in particles distributed in the large-size region decreases with increasing primary particle size. During the increase in primary particle size, there may be a partial plateau period, during which the molar percentage of Mn in particles in the large-size region remains constant.

[0126] In some implementations, the molar percentage of Mn in the particles exhibits a trend of constant-increase-constant-decrease-constant-constant as the primary particle size increases.

[0127] In some implementations, the molar percentage of Mn in particles distributed in the small-diameter region remains constant and then increases with the increase of the primary particle size.

[0128] In some implementations, the molar percentage of Mn in particles distributed in the medium-sized region shows a trend of increasing-remaining constant-decreasing with the increase of the primary particle size.

[0129] In some implementations, the molar percentage of Mn in particles distributed in the large-size region first decreases and then remains constant as the primary particle size increases.

[0130] Figure 2 shows the fitting curves of the molar proportion of Mn in particles distributed in the small particle size region, which first remains unchanged and then increases with the increase of the primary particle size; the molar proportion of Mn in particles distributed in the medium particle size region, which shows an increasing-unchanged-decreasing trend with the increase of the primary particle size; and the molar proportion of Mn in particles distributed in the large particle size region, which first decreases and then remains unchanged with the increase of the primary particle size.

[0131] When the molar percentage of Mn in each particle size region increases with the primary particle size as described above, the average molar percentage satisfies the design of the average molar percentage of Mn in each particle size region of this application. The secondary battery of this application has good compaction density, as well as good storage performance and good specific capacity.

[0132] In some implementations, the molar percentage of Mn in the particles varies continuously with the increase of the primary particle size.

[0133] In some implementations, the molar percentage of Mn in the particles varies discontinuously with increasing primary particle size.

[0134] In some embodiments, the primary particle size of particles distributed in the small particle size region is less than or equal to 180 nm and greater than or equal to 50 nm, the primary particle size of particles distributed in the medium particle size region is greater than 180 nm and less than 900 nm, and the primary particle size of particles distributed in the large particle size region is greater than or equal to 900 nm and less than or equal to 5 μm.

[0135] In some embodiments, the primary particle size of the particles distributed in the small particle size region can be 50nm, 60nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, or a value within the range of any two of the above primary particle sizes.

[0136] In some embodiments, the primary particle size of the particles distributed in the medium particle size region can be 181nm, 190nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 899nm, or a value within the range of any two of the above primary particle sizes.

[0137] When the primary particle size of particles in the small-diameter, medium-diameter, and large-diameter regions falls within the aforementioned range, it is beneficial to further improve the compaction density.

[0138] In some embodiments, in the positive electrode film layer, based on the total molar number of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small-diameter region is less than or equal to 12% and greater than or equal to 0%.

[0139] In some embodiments, in the positive electrode film layer, the molar percentage of Mn in the particles distributed in the small-diameter region is less than or equal to 8%, based on the total molar number of Mn in the lithium transition metal phosphate material.

[0140] In some embodiments, in the positive electrode film layer, the molar percentage of Mn in the particles distributed in the small-diameter region is less than or equal to 6%, based on the total molar number of Mn in the lithium transition metal phosphate material.

[0141] In this article, the term "molar number" refers to the number of specific particles contained in a substance, such as molecules and atoms.

[0142] In some embodiments, in the positive electrode film layer, based on the total number of moles of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small-diameter region 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 consisting of any two of the above molar percentages.

[0143] In the positive electrode film layer, based on the total molar number of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in particles distributed in the small-diameter region can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned test method for averaging the molar percentage of Mn in particles in the small-diameter region, the cross-sectional area S and the molar percentage X of Mn for each effective particle, as well as the cross-sectional area S and the molar percentage X of Mn for each effective particle in the small-diameter region, are measured.

[0144] Therefore, in the positive electrode film layer, based on the total molar number of Mn in the lithium-containing transition metal phosphate material, the formula for calculating the molar percentage of Mn in the particles distributed in the small-diameter region is as follows:

[0145] Where Xi and Xj represent the molar percentage of Mn in particles numbered i and j, respectively, and Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0146] Further controlling the molar ratio of Mn in the small-diameter region within a suitable range is beneficial to further improving the storage performance of the secondary battery in this application.

[0147] In some embodiments, in the positive electrode film layer, the molar percentage of Mn in the particles distributed in the small-diameter region is greater than or equal to 0.02%, based on the total molar number of Mn in the lithium transition metal phosphate material.

[0148] In any embodiment, in the positive electrode film layer, based on the total number of moles of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the particles distributed in the small particle size region is greater than or equal to 0.2%.

[0149] Small-diameter particles have better electrical conductivity. Compared to small-diameter particles that do not contain Mn, particles containing a certain amount of Mn help to improve the voltage plateau of the secondary voltage while also having better specific capacitance.

[0150] In some implementations, the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region is less than or equal to 0.8 and greater than or equal to 0.

[0151] In some implementations, the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region is less than or equal to 0.5.

[0152] In some embodiments, the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region can be 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, or 0.006. 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or a range consisting of any two of the above ratios, or a value within that range.

[0153] The ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned test method for the average molar percentage of Mn in particles in the large-size and medium-size regions, the average molar percentage of Mn in particles in both regions is measured.

[0154] The formula for calculating the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region is as follows:

[0155] Where Xi and Xj represent the molar percentage of Mn in particles numbered i and j, respectively, and Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0156] Further controlling the ratio of the average molar percentage of Mn in the large-size region particles to the average molar percentage of Mn in the medium-size region particles within a certain range, for example, controlling the ratio to be less than or equal to 0.8, and further less than or equal to 0.5, 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.

[0157] In some embodiments, the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region is greater than or equal to 0.0003.

[0158] In some embodiments, the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region is greater than or equal to 0.002.

[0159] By controlling the ratio of the average molar percentage of Mn in the large-size region to the average molar percentage of Mn in the medium-size region to be greater than 0, a certain amount of Mn is ensured in the large-size region particles. The large-size region particles can contribute a certain amount of platform capacity, 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 medium-size region particles on the battery's storage performance due to Mn dissolution. This makes the battery more suitable for application scenarios with certain storage performance requirements.

[0160] In some implementations, the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region is less than or equal to 0.8 and greater than or equal to 0.

[0161] In some implementations, the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region is less than or equal to 0.4.

[0162] In some embodiments, the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region can be 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, or 0. 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range of any two of the above ratios, or the values ​​between the ranges formed.

[0163] The ratio of the average molar percentage of Mn in particles distributed in the small-size region to the average molar percentage of Mn in particles distributed in the medium-size region can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned test method for the average molar percentage of Mn in particles in the small-size and medium-size regions, the average molar percentage of Mn in particles in both regions is measured.

[0164] The formula for calculating the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region is as follows:

[0165] Where Xi and Xj represent the molar percentage of Mn in particles numbered i and j, respectively, and Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0166] By further controlling the ratio of the average molar percentage of Mn in small-diameter particles to the average molar percentage of Mn in medium-diameter particles, for example, by further controlling the ratio to be less than or equal to 0.8 or less than or equal to 0.4, the secondary battery of this application has good volumetric energy density and its storage performance is further improved.

[0167] In some embodiments, the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region is greater than or equal to 0.0003.

[0168] In some embodiments, the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region is greater than or equal to 0.002.

[0169] Small-diameter particles have better electrical conductivity. Compared to small-diameter particles that do not contain Mn, particles containing a certain amount of Mn help to improve the voltage plateau of the secondary voltage while also having better specific capacitance.

[0170] In some implementations, the average manganese-iron molar ratio of particles distributed in the small-diameter region is less than or equal to 6:4 and greater than or equal to 0.

[0171] In some implementations, the average manganese-iron molar ratio of particles distributed in the small-diameter region is less than or equal to 4:6.

[0172] In some embodiments, the average manganese-iron molar ratio of particles distributed in the small-diameter region 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 range formed by any two of the above average manganese-iron molar ratios, or a value within such a range.

[0173] The average manganese-iron molar ratio of particles distributed in the small-size region can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned method for testing the average molar percentage of Mn in particles in the small-size region, the cross-sectional area S of the effective particles in the small-size region, the molar percentage X of Mn, and the molar percentage Y of Fe (again using EDS, where the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles) are measured.

[0174] The formula for calculating the average manganese-iron molar ratio of particles distributed in the small-diameter region is:

[0175] Where Xi represents the molar percentage of Mn in particle i, Yi represents the molar percentage of Fe in particle i, and Si represents the cross-sectional area of ​​particle i.

[0176] When the average manganese-iron molar ratio of particles in the small-diameter region is within a suitable range, it is beneficial to further reduce the side reactions between phosphate particles and electrolyte in the small-diameter region and the degree of manganese dissolution. As a result, the battery has a good volumetric energy density and its storage performance is further improved.

[0177] In some implementations, the average manganese-iron molar ratio of particles distributed in the small-diameter region is greater than or equal to 0.02:9.98.

[0178] By controlling the average manganese-iron molar ratio of particles in the small-diameter region to be greater than 0, the particles in the small-diameter region 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.

[0179] In some embodiments, the average manganese-iron molar ratio of particles distributed in the medium-sized particle region is greater than or equal to 4:6 and less than or equal to 9:1.

[0180] In some embodiments, the average manganese-iron molar ratio of particles distributed in the medium-sized particle region is greater than or equal to 5:5 and less than or equal to 9:1.

[0181] In some embodiments, the average manganese-iron molar ratio of particles distributed in the medium particle size region can be 9:1, 8:2, 7:3, 6:4, 5:5, or a range composed of any two of the above average manganese-iron molar ratios, or a value within such a range.

[0182] The average manganese-iron molar ratio of particles distributed in the medium particle size region can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned test method for the average molar percentage of Mn in particles in the medium particle size region, the cross-sectional area S, the molar percentage X of Mn, and the molar percentage Y of Fe in the effective particles of the medium particle size region are tested (again using EDS; the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles).

[0183] The formula for calculating the average manganese-iron molar ratio of particles distributed in the medium-sized particle region is:

[0184] Where Xi represents the molar percentage of Mn in particle i, Yi represents the molar percentage of Fe in particle i, and Si represents the cross-sectional area of ​​particle i.

[0185] Medium-sized 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 medium-sized particles within a suitable range is beneficial for increasing the total molar amount of manganese in the lithium transition metal phosphate material 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.

[0186] In some implementations, the average manganese-iron molar ratio of particles distributed in the large-size region is less than or equal to 6:4 and greater than or equal to 0.

[0187] In some implementations, the average manganese-iron molar ratio of particles distributed in the large-size region is less than or equal to 5:5.

[0188] In some embodiments, the average manganese-iron molar ratio of particles distributed in the large particle size region 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 range composed of any two of the above average manganese-iron molar ratios, or a value within the range.

[0189] The average manganese-iron molar ratio of particles distributed in the large-size region can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned method for testing the average molar percentage of Mn in particles in the large-size region, the cross-sectional area S, the molar percentage X of Mn, and the molar percentage Y of Fe in the effective particles of the large-size region are measured (again using EDS; the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles).

[0190] The formula for calculating the average manganese-iron molar ratio of particles distributed in the large-size region is:

[0191] Where Xi represents the molar percentage of Mn in particle i, Yi represents the molar percentage of Fe in particle i, and Si represents the cross-sectional area of ​​particle i.

[0192] When the average manganese-iron molar ratio of the large-diameter particles is within a suitable range, it can alleviate the discharge polarization of the large-diameter particles, improve the specific capacity, and the battery can have a good volumetric energy density while further improving its storage performance.

[0193] In some implementations, the average manganese-iron molar ratio of particles distributed in the large-size region is greater than or equal to 0.2:9.8.

[0194] In some implementations, the average manganese-iron molar ratio of particles distributed in the large-size region is greater than or equal to 1:9.

[0195] By controlling the average manganese-iron molar ratio of particles in the large-diameter region to be greater than 0, the particles in the large-diameter region have a certain voltage plateau, which can further improve the energy density of the battery.

[0196] In some implementations, the average manganese-iron molar ratio of the particles in the positive electrode film is greater than or equal to 2:8 and less than or equal to 9:1.

[0197] In some embodiments, the average manganese-iron molar ratio of the particles in the positive electrode film is greater than or equal to 2:8 and less than or equal to 6:4.

[0198] In some embodiments, the average manganese-iron molar ratio of the particles in the positive electrode film layer can be 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, or a range composed of any two of the above average manganese-iron molar ratios, or a value within that range.

[0199] The average manganese-iron molar ratio of the particles distributed in the positive electrode film can be determined using methods and equipment known in the art. A specific example is as follows: referring to the aforementioned method for testing the average molar percentage of Mn in the particles, the cross-sectional area S of the effective particles in the positive electrode film, the molar percentage X of Mn, and the molar percentage Y of Fe (again using EDS, where the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles) are measured.

[0200] The formula for calculating the average manganese-iron molar ratio of particles distributed in the positive electrode film is:

[0201] Where Xi represents the molar percentage of Mn in particle i, Yi represents the molar percentage of Fe in particle i, and Si represents the cross-sectional area of ​​particle i.

[0202] When the average manganese-iron molar ratio of the particles in the positive electrode film is within a suitable range, lithium-containing transition metal phosphate materials 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.

[0203] In some implementations, based on the total area of ​​particles in the positive electrode film, the area percentage of particles distributed in the small-diameter region is greater than 0% and less than or equal to 30%; and / or

[0204] The area of ​​particles distributed in the medium-sized region is greater than or equal to 20% and less than 100%; and / or,

[0205] The area of ​​particles distributed in the large-size region is greater than 0% and less than or equal to 80%.

[0206] In some implementations, based on the total area of ​​particles in the positive electrode film, the area percentage of particles distributed in the small-diameter region is greater than or equal to 5% and less than or equal to 15%; and / or,

[0207] The area of ​​particles distributed in the medium-sized region is greater than or equal to 40% and less than or equal to 85%; and / or,

[0208] The area of ​​particles distributed in the large-size region is greater than or equal to 5% and less than or equal to 40%.

[0209] In some implementations, based on the total area of ​​the particles in the positive electrode film, the area percentage of particles distributed in the small-diameter region can be 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 a range of any two area percentages or a value within that range.

[0210] In some implementations, based on the total area of ​​the particles in the positive electrode film, the area percentage of the particles distributed in the medium particle size region can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, or any range of two area percentages, or a value within such a range.

[0211] In some implementations, based on the total area of ​​the particles in the positive electrode film, the area percentage of particles in the large-diameter region can be 0.1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any range of two area percentages, or a value within such a range.

[0212] The test methods for determining the area ratio of particles in the small-diameter region, the medium-diameter region, and the large-diameter region can be performed using methods and equipment known in the art. For example, the cross-sectional area S of each particle can be determined by referring to the aforementioned test method for measuring the average molar ratio of Mn in particles in the small-diameter, medium-diameter, and large-diameter regions.

[0213] The formula for calculating the area ratio of particles in the small-diameter region is as follows:

[0214] The formula for calculating the area ratio of particles in the medium-sized region is as follows:

[0215] The formula for calculating the area ratio of particles in the large-diameter region is as follows:

[0216] Where Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0217] When the area ratio of medium-sized particles is within a suitable range, the battery exhibits superior volumetric energy density and storage performance. When the area ratio of small-sized particles is within a suitable range, the battery exhibits superior compaction density, volumetric energy density, and storage performance. When the area ratio of large-sized particles is within a suitable range, lithium-containing transition metal phosphate materials exhibit superior powder compaction density, specific capacity, and storage life, resulting in superior volumetric energy density and storage performance.

[0218] In some embodiments, the particles distributed in the small-diameter region 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, 3.5 ≤ n1 ≤ 4, 0 ≤ a1 ≤ 0.1, 0 ≤ b1 ≤ 0.1, 0 ≤ c1 ≤ 0.1, 0 ≤ d1 ≤ 0.1; and / or,

[0219] Particles distributed in the medium-sized region 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, 3.5 ≤ n2 ≤ 4, 0 ≤ a2 ≤ 0.1, 0 ≤ b2 ≤ 0.1, 0 ≤ c2 ≤ 0.1, 0 ≤ d2 ≤ 0.1; and / or,

[0220] Particles distributed in the medium-sized region have the molecular formula Li m3 A3 a3 Fex3 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, 3.5≤n3≤4, 0≤a3≤0.1, 0≤b3≤0.1, 0≤c3≤0.1, and 0≤d3≤0.1.

[0221] 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.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] 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 enhance the storage performance of the material.

[0227] 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.

[0228] Choosing appropriate modifying elements A1, A2, and A3 can also improve the lattice change rate of the material and maintain its battery capacity.

[0229] 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 storage performance of the positive electrode active material. Furthermore, it can enhance the material's resistance to acid corrosion such as HF, thereby improving its storage performance and lifespan.

[0230] 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.

[0231] In some embodiments, the positive electrode film layer includes a positive electrode active material, which includes a lithium transition metal phosphate material, 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 / cm³ 3 .

[0232] 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 2.45g / cm 3 2.5g / cm 3 2.55g / cm 3 2.60g / cm 3 2.65g / cm 3, or a range consisting of any two of the above powder compaction densities, or a value within that range.

[0233] 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.

[0234] The higher the powder compaction density, the higher the mass of powder material per unit volume. When the powder compaction density of the positive electrode active material 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.

[0235] 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.

[0236] In some embodiments, the specific capacity of the positive electrode active material at 40°C and a 1 / 3C discharge rate can be 150mAh / g, 149mAh / g, 148mAh / g, 14mAh / 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 any range of two of the above specific capacities.

[0237] The 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.

[0238] [Preparation of positive electrode active materials]

[0239] This application also provides a method for preparing a positive electrode active material:

[0240] A lithium-containing transition metal phosphate material is obtained by mixing a first lithium-containing transition metal phosphate material, a second lithium-containing transition metal phosphate material, and a third lithium-containing transition metal phosphate material.

[0241] 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.

[0242] 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, and 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.

[0243] The average molar percentage of Mn in the second lithium-containing transition metal phosphate material is greater than the average molar percentage of Mn in the first lithium-containing transition metal phosphate material and the average molar percentage of Mn in the first lithium-containing transition metal phosphate material, respectively. Here, the molar percentage of Mn refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0244] The first lithium-containing transition metal phosphate material can include a variety of lithium-containing transition metal phosphate materials with different primary particle sizes.

[0245] The second lithium-containing transition metal phosphate material can include a variety of lithium-containing transition metal phosphate materials with different primary particle sizes.

[0246] The third type of lithium-containing transition metal phosphate material can include a variety of lithium-containing transition metal phosphate materials with different primary particle sizes.

[0247] In this paper, the term "primary average particle size" refers to the average primary particle size of all particles.

[0248] The primary average particle size of lithium transition metal phosphate materials can be measured using methods and equipment known in the art. For example, it can be tested using transmission electron microscopy (TEM) and the equivalent circle method, as illustrated 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 sonicated at a power of 480 W for 5 min to obtain a uniformly dispersed suspension. An appropriate amount of the intermediate suspension is then subjected to TEM testing. 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 primary particle diameters 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.

[0249] The average molar percentage of Mn in lithium-containing transition metal phosphate materials can be measured using methods and equipment known in the art. A specific example is as follows: The molar content of Mn and Fe elements is tested according to the chemical analysis method for nano-lithium iron phosphate in national standard GB / T 33822-2017, and the average molar percentage of Mn in the material can then be calculated.

[0250] In some embodiments, the primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm to 200 nm.

[0251] In some embodiments, the primary average particle size of the first lithium-containing transition metal phosphate material can be 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, or a range of any two of the above primary average particle sizes, or a value within that range.

[0252] In some embodiments, the primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm to 600 nm.

[0253] In some implementation methods, the primary average particle size of the second lithium-containing transition metal phosphate material can be 120nm, 140nm, 160nm, 180nm, 200nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, 560nm, 580nm, or 600nm, or a range composed of any two of the above primary average particle sizes, or a value within the range.

[0254] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material is 250 nm to 4000 nm.

[0255] In some embodiments, the primary average particle size of the third lithium-containing transition metal phosphate material can be 250 nm, 450 nm, 650 nm, 850 nm, 870 nm, 1050 nm, 1250 nm, 1450 nm, 1650 nm, 1850 nm, 2050 nm, 2250 nm, 2450 nm, 2650 nm, 2850 nm, 3050 nm, 3250 nm, 3450 nm, 3650 nm, 3850 nm, or 4000 nm, or a range of any two of the above primary average particle sizes, or a value within that range.

[0256] In some embodiments, based on the total molar number of Mn in the lithium transition metal phosphate material, the molar percentage of Mn in the first lithium transition metal phosphate particle is less than or equal to 50% and greater than or equal to 0%.

[0257] 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 particle 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.

[0258] 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 a 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).

[0259] 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.

[0260] 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.

[0261] 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.

[0262] 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, 4:6, 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 range formed by any two of the above average manganese-iron molar ratios, or a value within that range.

[0263] 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, or a range formed by any two of the above-mentioned average manganese-iron molar ratios, or a value within such a range.

[0264] 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.

[0265] 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 range composed of any two of the above average manganese-iron molar ratios, or a value within that range.

[0266] 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.

[0267] 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、11m2 / 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.

[0268] 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.

[0269] 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.

[0270] 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.

[0271] 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.

[0272] 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.

[0273] 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.

[0274] 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.

[0275] 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.

[0276] In some embodiments, the third lithium-containing transition metal phosphate material satisfies at least one of (a)-(f):

[0277] (a) The Dv10 of the third lithium-containing transition metal phosphate material is ≥0.2 μm;

[0278] (b) The Dv50 of the third lithium-containing transition metal phosphate material is 0.5-5 μm;

[0279] (c) The Dv90 of the third lithium-containing transition metal phosphate material is ≤10μm;

[0280] (d) The Dv99 of the third lithium-containing transition metal phosphate material is ≤12μm;

[0281] (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 ;

[0282] (f) The resistivity of the third lithium-containing transition metal phosphate material is less than 60 Ω·cm.

[0283] In this paper, the term "Dv10" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 10%.

[0284] In this paper, the term "Dv50" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 10%.

[0285] In this paper, the term "Dv90" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 90%.

[0286] In this paper, the term "Dv99" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 99%.

[0287] In some embodiments, the third lithium-containing transition metal phosphate material has a Dv10 < Dv50.

[0288] In some embodiments, the Dv90 of the third lithium-containing transition metal phosphate material is greater than the Dv50.

[0289] 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.

[0290] 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.

[0291] The compacted density of the third lithium-containing transition metal phosphate material can be measured using a compaction density instrument, referring to GB / T24533-2009. Specifically, a certain amount of material 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 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.

[0292] 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.

[0293] In some embodiments, based on the total weight of the lithium-containing transition metal phosphate material, the weight percentage of the first lithium-containing transition metal phosphate material is greater than 0% and less than or equal to 30%; and / or,

[0294] The second lithium-containing transition metal phosphate material has a weight percentage greater than or equal to 15% and less than 100%; and / or,

[0295] The third lithium-containing transition metal phosphate material has a weight percentage greater than 0% and less than or equal to 85%.

[0296] In some embodiments, based on the total weight of the lithium-containing transition metal phosphate material, the weight percentage of the first lithium-containing transition metal phosphate material is greater than or equal to 3% and less than or equal to 15%; and / or,

[0297] The second lithium-containing transition metal phosphate material has a weight percentage greater than or equal to 30% and less than or equal to 85%; and / or,

[0298] The third lithium-containing transition metal phosphate material has a weight percentage of greater than or equal to 10% and less than or equal to 67%.

[0299] 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%, 1%, or a value within a range of any two of the above weight percentages.

[0300] 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.

[0301] 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 1%, 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.

[0302] 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 ,

[0303] 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

[0304] 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

[0305] 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 ,

[0306] 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

[0307] 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.

[0308] 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.

[0309] 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.

[0310] 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.

[0311] 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.

[0312] 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.

[0313] [Positive electrode plate]

[0314] 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.

[0315] 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.

[0316] In some embodiments, the positive electrode film layer further includes a binder and a conductive agent.

[0317] In some embodiments, the mass ratio of the positive electrode active material, binder, and conductive agent in the positive electrode film layer is (92-99):(0.5-3):(0.5-3).

[0318] In some embodiments, the coating weight on one side of the positive electrode is 300 mg / 1540 mm. 2 -580mg / 1540mm 2 .

[0319] 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 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. Residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and then cut into pieces with an area of ​​1540 mm². 2 The small circular sheet is weighed as M. Then, the positive electrode film layer of the weighed electrode sheet is wiped off, and the weight of the current collector is weighed and recorded as N. Then, the weight of the single-sided coating is (MN) / 2.

[0320] 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 420mg / 1540mm2 460mg / 1540mm 2 500mg / 1540mm 2 540mg / 1540mm 2 580mg / 1540mm 2 Or any value in between.

[0321] When the coating weight of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0322] In some embodiments, the compaction density of the positive electrode sheet is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0323] 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).

[0324] 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.

[0325] When the compaction density of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0326] 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.

[0327] 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.

[0328] 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.

[0329] 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).

[0330] 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.

[0331] [Negative electrode plate]

[0332] 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.

[0333] 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.

[0334] 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.).

[0335] 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.

[0336] 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).

[0337] 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.

[0338] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0339] 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.

[0340] [Electrolytes]

[0341] 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.

[0342] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0343] 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.

[0344] 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.

[0345] 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.

[0346] [Isolation membrane]

[0347] 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.

[0348] 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.

[0349] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0350] 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.

[0351] 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.

[0352] [Rechargeable Battery]

[0353] In one embodiment of this application, a secondary battery is provided, including a positive electrode, a separator, a negative electrode, and an electrolyte.

[0354] In some embodiments, the secondary battery is a lithium-ion battery or a sodium-ion battery. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. A separator is disposed between the positive and negative electrode plates, primarily to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0355] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0356] 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.

[0357] 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.

[0358] 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 5 shows a square secondary battery 5 as an example.

[0359] In some embodiments, referring to FIG6, 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.

[0360] 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.

[0361] Figure 7 shows a battery module 4 as an example. Referring to Figure 7, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0362] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0363] 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.

[0364] Figures 8 and 9 illustrate a battery pack 1 as an example. Referring to Figures 8 and 9, the battery pack 1 may include a battery compartment and multiple battery modules 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, with the upper compartment 2 covering the lower compartment 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 compartment.

[0365] [Electrical appliances]

[0366] 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.

[0367] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0368] Figure 10 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.

[0369] 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.

[0370] Example

[0371] 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.

[0372] I. Preparation Method

[0373] Example 1

[0374] (1) Preparation of positive electrode active material

[0375] Material A is LiMn 0.396 Fe 0.594 Ti 0.005 PO4 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-EM-E4012). Material A mainly consists of particles with a primary diameter of less than or equal to 180nm and greater than or equal to 50nm. The presence of particles with a diameter greater than 180nm cannot be ruled out. The primary average particle size of material A is 120nm, and the average molar ratio of Mn is 0.4.

[0376] Material B is LiMn 0.594 Fe 0.396 Ti 0.005 PO4 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-FM-F6040). Material B mainly consists of particles with a primary diameter greater than 180nm and less than 900nm. It is possible that there are particles with a primary diameter less than or equal to 180nm and a primary diameter greater than or equal to 900nm. The primary average particle size of particle B is 400nm, and the average molar ratio of Mn is 0.6.

[0377] Material C is LiMn 0.396 Fe 0.594 Ti 0.005 PO4 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-GM-G4065). 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 650 nm, and the average molar percentage of Mn is 0.4.

[0378] (2) Preparation of positive electrode sheet

[0379] Materials A, B, and C are mixed in a mass ratio of 5:80:15 to obtain a positive electrode active material. The above-mentioned mixed positive electrode active material, conductive agent conductive carbon black, and binder polyvinylidene fluoride are mixed 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.

[0380] 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 .

[0381] (3) Preparation of negative electrode sheet:

[0382] 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.

[0383] (4) Battery fabrication:

[0384] 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.

[0385] Example 2

[0386] The difference between Example 2 and Example 1 lies in the different positive electrode active materials. Material A is a mixture of materials A1, A2, A3 and A4, with the mass percentages of materials A1, A2, A3 and A4 being 25%, 25%, 25% and 25%, respectively.

[0387] Material B is a mixture of materials B1, B2, B3 and B4, with the mass percentages of materials B1, B2, B3 and B4 being 25%, 25%, 25% and 25%, respectively.

[0388] Material C is a mixture of materials C1, C2, C3 and C4, with the mass percentages of materials C1, C2, C3 and C4 being 25%, 25%, 25% and 25%, respectively.

[0389] The specific material composition is shown in the table below:

[0390] Comparative Example 1

[0391] The difference between Comparative Example 1 and Example 1 is that the positive electrode active material in Comparative Example 1 only includes material B, excluding materials A and C. Material B is LiMn. 0.59 4Fe 0.396 Ti 0.005 PO4 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-FM-F6050). The primary average particle size of material B is 500 nm, and the average molar ratio of Mn is 0.6.

[0392] Comparative Example 2

[0393] The difference between Comparative Example 2 and Example 1 is that the molar ratio of manganese to iron in materials A and C is greater than that in material B. Specifically...

[0394] Material A is LiMn 0.693 Fe 0.297 Ti 0.005 PO4 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-EM-E7011). The primary average particle size of material A is 110 nm, and the average molar ratio of Mn is 0.7.

[0395] Material B is LiMn 0.594 Fe 0.396 Ti 0.005 PO4, purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-FM-F6040), has a primary average particle size of 400 nm for particles B and an average molar percentage of 0.6 for Mn.

[0396] Material C is LiMn 0.693 Fe 0.297 Ti 0.005 PO4 was purchased from Guangdong Bangpu Recycling Technology Co., Ltd. (BP-GM-G7070). The primary average particle size of material C is 700 nm, and the average molar ratio of Mn is 0.7.

[0397] II. Performance Testing

[0398] 1. Characteristic testing of positive electrode active materials

[0399] 1) Determination of the average molar ratio of Mn in particles of small diameter, medium diameter, and large diameter regions.

[0400] The battery was disassembled to obtain the positive electrode sheet. The positive electrode film layer of the positive electrode sheet was peeled off, and the positive electrode film layer was thoroughly washed with acetone to remove binders and dispersants. After filtration and drying, powder was obtained. 0.05g of the uniformly mixed powder was dissolved in 40ml of anhydrous ethanol, and then an appropriate amount of dispersant was added. The mixture was stirred evenly to obtain a suspension. 2ml of the suspension was mixed with 2ml of anhydrous ethanol and then subjected to ultrasonic treatment at a power of 480W for 5min. A uniformly dispersed suspension was obtained. An appropriate amount of the middle layer suspension was 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 was calculated, which is the cross-sectional area S of the primary particle. The equivalent circle diameter of the primary particle was obtained using the equivalent circle method, which is the primary particle diameter d. In the above statistical process of primary particles and their primary particle diameters, primary particles with a primary particle diameter less than 50nm and greater than 5μm were 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). Simultaneously, EDS point scanning can be used to test the Mn and Fe content of each effective particle in the transmission electron microscope image, and the molar percentage of Mn in each effective particle X can be calculated (the molar percentage 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 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, and their cross-sectional area S, primary diameter d, and molar ratio X of Mn were measured. The obtained effective particles were then numbered from smallest to largest primary diameter as 1, 2, 3, 4, 5…n. The m-th particle had a primary diameter less than or equal to 180 nm, the (m+1)-th particle had a primary diameter greater than 180 nm, the (k-1)-th particle had a primary diameter less than 900 nm, and the k-th particle had a primary diameter greater than or equal to 900 nm but less than or equal to 5 μm. Particles 1 to m were designated as the small-diameter region, particles (m+1) to (k-1)-th particles as the medium-diameter region, and particles (k to n)-th particles as the large-diameter region.

[0401] The formula for calculating the average molar percentage of Mn in the small-diameter region is as follows:

[0402] The formula for calculating the average molar percentage of Mn in particles of medium size is as follows:

[0403] The formula for calculating the average molar percentage of Mn in particles with large particle size is as follows:

[0404] Where Xi represents the molar percentage of Mn in particle number i, and Si represents the cross-sectional area of ​​particle number i.

[0405] 2) Determination of the molar percentage of Mn in particles distributed in small-diameter regions based on the total molar number of Mn in lithium-containing transition metal phosphate materials.

[0406] Referring to the test method for the average molar percentage of Mn in the small-diameter region of particles mentioned in 1) above, the cross-sectional area S and the molar percentage X of Mn for each effective particle, as well as the cross-sectional area S and the molar percentage X of Mn for each effective particle in the small-diameter region, were tested.

[0407] Therefore, in the positive electrode film layer, based on the total molar number of Mn in the lithium-containing transition metal phosphate material, the formula for calculating the molar percentage of Mn in the particles distributed in the small-diameter region is as follows:

[0408] Where Xi and Xj represent the molar percentage of Mn in particles numbered i and j, respectively, and Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0409] 3) The ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region, and the ratio of the average molar percentage of Mn in particles distributed in the small-size region to the average molar percentage of Mn in particles distributed in the medium-size region were determined.

[0410] Referring to the aforementioned method for testing the average molar percentage of Mn in particles in the small-diameter, large-diameter, and medium-diameter regions (1), the average molar percentage of Mn in particles in these regions was measured.

[0411] The formula for calculating the ratio of the average molar percentage of Mn in particles distributed in the large-size region to the average molar percentage of Mn in particles distributed in the medium-size region is as follows:

[0412] The formula for calculating the ratio of the average molar percentage of Mn in particles distributed in the small-diameter region to the average molar percentage of Mn in particles distributed in the medium-diameter region is as follows:

[0413] Where Xi and Xj represent the molar percentage of Mn in particles numbered i and j, respectively, and Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0414] 4) Determination of the average manganese-iron molar ratio of particles distributed in the small-particle-size region, medium-particle-size region, large-particle-size region, and positive electrode film layer.

[0415] Referring to the aforementioned method for testing the average molar percentage of Mn in particles in the small-diameter region, medium-diameter region, large-diameter region, and positive electrode film layer, the cross-sectional area S, molar percentage X of Mn, and molar percentage Y of Fe in the effective particle size region were tested (using EDS, where the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles). Similarly, the cross-sectional area S, molar percentage X of Mn, and molar percentage Y of Fe in the effective particle size region were tested (using EDS, where the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles). The cross-sectional area S, the molar percentage X of Mn, and the molar percentage Y of Fe in the large-particle region were measured using EDS (Electrode Sequencing), where the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles. The cross-sectional area S, the molar percentage X of Mn, and the molar percentage Y of Fe in the effective particles of the positive electrode film were also measured using EDS (Electrode Sequencing), where the molar percentage of Fe refers to the content of Fe moles relative to the total number of Mn and Fe moles.

[0416] The formula for calculating the average manganese-iron molar ratio of particles distributed in the small-diameter region is:

[0417] The formula for calculating the average manganese-iron molar ratio of particles distributed in the medium-sized particle region is:

[0418] The formula for calculating the average manganese-iron molar ratio of particles distributed in the large-size region is:

[0419] The formula for calculating the average manganese-iron molar ratio of the particles distributed in the positive electrode film is:

[0420] Where Xi represents the molar percentage of Mn in particle i, Yi represents the molar percentage of Fe in particle i, and Si represents the cross-sectional area of ​​particle i.

[0421] 5) Determination of the area ratio of particles in the small-diameter region, the medium-diameter region, and the large-diameter region.

[0422] Referring to the test method described in section 1) above, which measures the average molar percentage of Mn in the small-diameter, medium-diameter, and large-diameter regions, the cross-sectional area S of each particle was determined.

[0423] The formula for calculating the area ratio of particles in the small-diameter region is as follows:

[0424] The formula for calculating the area ratio of particles in the medium-sized region is as follows:

[0425] The formula for calculating the area ratio of particles in the large-diameter region is as follows:

[0426] Where Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0427] 6) Molar ratio of Mn in particles versus primary particle size curve

[0428] Referring to the test method described in 1) above, the primary particle size d and the molar percentage X of Mn in each effective particle were measured. The parameters of each effective particle were plotted with the primary particle size as the x-axis and the molar percentage of Mn as the y-axis, and a curve was obtained through statistical fitting. Where multiple particles exist within a given particle size, and the molar percentage of Mn differs among different particles, the molar percentage X of Mn within that particle size is the average of the molar percentages of Mn among different particles of the same particle size.

[0429] 2. Secondary battery performance test

[0430] 1) Specific capacity of secondary batteries

[0431] Place the battery in a 40℃ oven and let it stand for 2 hours until the battery temperature remains at 40℃. 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, and then charge it at a constant voltage of 4.1V until the cutoff current is 0.05C. Pause for 5 minutes. Discharge the battery at a constant current of 1 / 3C to 2.0V. This step is the actual cell test capacity C.

[0432] 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.

[0433] 2) Storage performance of secondary batteries

[0434] 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. After a 5-minute pause, 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. Pause for 5 minutes. Then, discharge the battery at a constant current of 1 / 3C to 2.0V. This completes 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 decreases to 80%. Record the storage time at this point.

[0435] 3) Secondary volumetric energy density

[0436] Battery cell capacity test: The battery cell was left to stand at 40℃ for 2 hours to ensure the temperature of the battery cell was 40℃. Then the battery was discharged at 1 / 3C constant current to 2.0V. After standing for 5 minutes, the battery cell was charged at 1 / 3C constant current to 4.1V. The constant voltage charging at 4.1V continued until the current was 0.05C. After standing for 5 minutes, the battery cell was discharged at 1 / 3 constant current to 2.0V. The total discharge energy released by the battery cell was recorded as E0. The unit of total discharge energy is Wh.

[0437] 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).

[0438] 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.

[0439] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0440] 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.

[0441] Table 1. Parameters of Secondary Batteries

[0442] Continued from Table 1

[0443] Continued from Table 1

[0444] Table 2 Performance parameters of positive electrode active materials and secondary batteries

[0445] In the secondary battery of this application, when the average molar percentage of Mn in the particles distributed in the medium-diameter region is higher than that in the particles distributed in the small-diameter region and the particles distributed in the large-diameter region, the secondary battery of this application has better compaction density and volumetric energy density, as well as better specific capacity and storage performance.

[0446] As can be seen from Examples 1-2 and Comparative Example 1, when the positive electrode active material includes particles in small-diameter, medium-diameter, and large-diameter regions, it helps to improve the compaction density of the secondary battery, thereby further improving the volumetric energy density.

[0447] Furthermore, as can be seen from Examples 1-2 and Comparative Examples 1-2, controlling the average molar percentage of Mn in particles distributed in the medium-sized region to be higher than the average molar percentage of Mn in particles distributed in the small-sized region and the average molar percentage of Mn in particles distributed in the large-sized region helps to improve the specific capacity and storage performance of the secondary battery.

[0448] Figure 2 shows the molar ratio of Mn in the particles of Example 1 versus the primary particle size curve. As the primary particle size increases, the molar ratio of Mn in the particles shows a trend of constant-increase-constant-decrease-constant. Specifically, in the small particle size region, the molar ratio of Mn in the particles shows a trend of constant-increase as the primary particle size increases; in the medium particle size region, the molar ratio of Mn in the particles shows a trend of increase-constant-decrease as the primary particle size increases; and in the large particle size region, the molar ratio of Mn in the particles shows a trend of decrease-constant.

[0449] Figure 3 shows the molar percentage of Mn versus the primary particle size curve of Example 2. As the primary particle size increases, the molar percentage of Mn in the particles first increases and then decreases. Specifically, in the small particle size region, the molar percentage of Mn in the particles increases with the increase of the primary particle size; in the medium particle size region, the molar percentage of Mn in the particles first increases and then decreases with the increase of the primary particle size; and in the large particle size region, the molar percentage of Mn in the particles decreases with the increase of the primary particle size. During the process of increasing the primary particle size, there may be a plateau period in which the molar percentage of Mn in the particles remains unchanged with the increase of the primary particle size.

[0450] As shown in Examples 1 and 2, based on the total molar number of Mn in the lithium transition metal phosphate material, when the molar percentage of Mn in the particles distributed in the small-diameter region and / or the average molar percentage of Mn in the particles distributed in the small-diameter region are within a suitable range compared to the average molar percentage of Mn in the particles distributed in the medium-diameter region, for example, when the molar percentage of Mn in the particles distributed in the small-diameter region is less than 6% based on the total molar number of Mn in the lithium transition metal phosphate material, and / or the average molar percentage of Mn in the particles distributed in the small-diameter region is less than or equal to 0.4, the secondary battery exhibits better storage performance. When the average molar percentage of Mn in the particles distributed in the large-diameter region is within a suitable range compared to the average molar percentage of Mn in the particles distributed in the medium-diameter region, for example, less than 0.5, the secondary battery exhibits better storage performance and better specific capacity utilization.

[0451] 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 particles with different primary particle sizes, the particles comprise a lithium-containing transition metal phosphate material, the average mole percentage of Mn of the particles distributed in a medium particle size region is higher than the average mole percentage of Mn of the particles distributed in a small particle size region and the average mole percentage of Mn of the particles distributed in a large particle size region, respectively, wherein the mole percentage of Mn refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

2. The secondary battery according to claim 1, characterized by The average mole percentage of Mn of the particles distributed in the medium particle size region is higher than the average mole percentage of Mn of the particles distributed in the small particle size region and the average mole percentage of Mn of the particles distributed in the large particle size region, respectively.

3. The secondary battery according to claim 1 or 2, characterized by The mole percentage of Mn of the particles distributed in the small particle size region changes arbitrarily with the increase of the primary particle size of the particles; and / or, The mole percentage of Mn of the particles distributed in the medium particle size region changes arbitrarily with the increase of the primary particle size of the particles; The mole percentage of Mn of the particles distributed in the large particle size region changes arbitrarily with the increase of the primary particle size of the particles.

4. The secondary battery according to any one of claims 1 to 3, characterized by, The mole percentage of Mn of the particles increases first and then decreases with the increase of the primary particle size of the particles.

5. The secondary battery according to any one of claims 1 to 4, characterized by, The mole percentage of Mn of the particles distributed in the small particle size region increases with the increase of the primary particle size of the particles; and / or, The mole percentage of Mn of the particles distributed in the medium particle size region increases first and then decreases with the increase of the primary particle size of the particles; and / or, The mole percentage of Mn of the particles distributed in the large particle size region decreases with the increase of the primary particle size of the particles.

6. The secondary battery according to any one of claims 1 to 3, characterized by, The mole percentage of Mn of the particles presents the trend of unchanged-increase-unchanged-decrease-unchanged with the increase of the primary particle size of the particles.

7. The secondary battery according to any one of claims 1 to 3, 6, characterized by, The mole percentage of Mn of the particles distributed in the small particle size region changes first and then increases with the increase of the primary particle size of the particles; and / or, The mole percentage of Mn of the particles distributed in the medium particle size region presents the trend of increase-unchanged-decrease with the increase of the primary particle size of the particles; and / or, The mole percentage of Mn of the particles distributed in the large particle size region changes first and then remains unchanged with the increase of the primary particle size of the particles.

8. The secondary battery according to any one of claims 1-7, characterized by, The mole percentage of Mn of the particles changes continuously or discontinuously with the increase of the primary particle size of the particles.

9. The secondary battery according to any one of claims 1-8, characterized by, The primary particle size of the particles distributed in the small particle size region is less than or equal to 180 nm and greater than or equal to 50 nm, the primary particle size of the particles distributed in the medium particle size region is greater than 180 nm and less than 900 nm, and the primary particle size of the particles distributed in the large particle size region is greater than or equal to 900 nm and less than or equal to 5 μm.

10. The secondary battery according to any one of claims 1-9, characterized in that, In the positive electrode film layer, the mole percentage of Mn of the particles distributed in the small particle size region is less than or equal to 12% and greater than or equal to 0%, based on the total number of moles of Mn in the lithium-containing transition metal phosphate material.

11. The secondary battery according to any one of claims 1-10, characterized in that, In the positive electrode film layer, the molar percentage of Mn of the particles distributed in the small particle size region is less than or equal to 8% based on the total moles of Mn in the lithium-containing transition metal phosphate material.

12. The secondary battery according to any one of claims 1-12, characterized in that, In the positive electrode film layer, the molar percentage of Mn of the particles distributed in the small particle size region is less than or equal to 6% based on the total moles of Mn in the lithium-containing transition metal phosphate material.

13. The secondary battery according to any one of claims 1-12, characterized by, In the positive electrode film layer, the molar percentage of Mn of the particles distributed in the small particle size region is greater than or equal to 0.02% based on the total moles of Mn in the lithium-containing transition metal phosphate material.

14. The secondary battery according to any one of claims 1-13, characterized by, In the positive electrode film layer, the molar percentage of Mn of the particles distributed in the small particle size region is greater than or equal to 0.2% based on the total moles of Mn in the lithium-containing transition metal phosphate material.

15. The secondary battery according to any one of claims 1-14, characterized by, The ratio of the average molar percentage of Mn of the particles distributed in the large particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is less than or equal to 0.8, greater than or equal to 0.

16. The secondary battery according to any one of claims 1-17, characterized by, The ratio of the average molar percentage of Mn of the particles distributed in the large particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is less than or equal to 0.

5.

17. The secondary battery according to any one of claims 1-16, characterized by The ratio of the average molar percentage of Mn of the particles distributed in the large particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is greater than or equal to 0.0003.

18. The secondary battery according to any one of claims 1-17, characterized by, The ratio of the average molar percentage of Mn of the particles distributed in the large particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is greater than or equal to 0.

002.

19. The secondary battery according to any one of claims 1-18, characterized by, The ratio of the average molar percentage of Mn of the particles distributed in the small particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is less than or equal to 0.8, greater than or equal to 0.

20. The secondary battery according to any one of claims 1-19, wherein, The ratio of the average molar percentage of Mn of the particles distributed in the small particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is less than or equal to 0.

4.

21. The secondary battery according to any one of claims 1-20, characterized by The ratio of the average molar percentage of Mn of the particles distributed in the small particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is greater than or equal to 0.0003.

22. The secondary battery according to any one of claims 1-21, characterized by, The ratio of the average molar percentage of Mn of the particles distributed in the small particle size region to the average molar percentage of Mn of the particles distributed in the medium particle size region is greater than or equal to 0.

002.

23. The secondary battery according to any one of claims 1-22, characterized by, The average molar ratio of manganese to iron of the particles distributed in the small particle size region is less than or equal to 6:4, greater than or equal to 0.

24. The secondary battery according to any one of claims 1-23, characterized by, The average molar ratio of manganese to iron of the particles distributed in the small particle size region is less than or equal to 4:

6.

25. The secondary battery according to any one of claims 1-24, characterized by, The average molar ratio of manganese to iron of the particles distributed in the small particle size region is greater than or equal to 0.02:9.

98.

26. The secondary battery according to any one of claims 1-25, wherein The average molar ratio of manganese to iron of the particles distributed in the medium particle size region is greater than or equal to 4:6, less than or equal to 9:

1.

27. The secondary battery according to any one of claims 1-26, characterized by, The average molar ratio of manganese to iron of the particles distributed in the medium particle size region is greater than or equal to 5:5, less than or equal to 9:

1.

28. The secondary battery according to any one of claims 1-27, wherein The average molar ratio of manganese to iron of the particles distributed in the large particle size region is less than or equal to 6:4, greater than or equal to 0.

29. The secondary battery according to any one of claims 1-28, wherein The average molar ratio of manganese to iron of the particles distributed in the large particle size region is less than or equal to 5:

5.

30. The secondary battery according to any one of claims 1-29, wherein The average molar ratio of manganese to iron of the particles distributed in the large particle size region is greater than or equal to 0.2:9.

8.

31. The secondary battery according to any one of claims 1-30, wherein The average molar ratio of manganese to iron of the particles distributed in the large particle size region is greater than or equal to 1:

9.

32. The secondary battery according to any one of claims 1-31, wherein The average molar ratio of manganese to iron of the particles in the positive electrode film layer is greater than or equal to 2:8 and less than or equal to 9:

1.

33. The secondary battery according to any one of claims 1-32, wherein The average molar ratio of manganese to iron of the particles in the positive electrode film layer is greater than or equal to 2:8 and less than or equal to 6:

4.

34. The secondary battery according to any one of claims 1-33, wherein Based on the total area of the particles in the positive electrode film layer, the area percentage of the particles distributed in the small particle size region is greater than 0% and less than or equal to 30%; and / or, The area percentage of the particles distributed in the medium particle size region is greater than or equal to 20% and less than 100%; and / or, The area percentage of the particles distributed in the large particle size region is greater than 0% and less than or equal to 80%.

35. The secondary battery according to any one of claims 1-34, wherein Based on the total area of the particles in the positive electrode film layer, the area percentage of the particles distributed in the small particle size region is greater than or equal to 5% and less than or equal to 15%; and / or, The area percentage of the particles distributed in the medium particle size region is greater than or equal to 40% and less than or equal to 85%; and / or, The area percentage of the particles distributed in the large particle size region is greater than or equal to 5% and less than or equal to 40%.

36. The secondary battery according to any one of claims 1-35, wherein The particles distributed in the small particle size region have a 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, Mg, M1 includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1 includes one or more of B, S, Si, N, N1 includes 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, said particles distributed in the medium particle size region 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 particles distributed in the medium particle size region have a molecular 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.

37. The secondary battery according to any one of claims 1-36, wherein The positive electrode film layer includes a positive electrode active material, the positive electrode active material including the lithium-containing transition metal phosphate material, 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 .

38. The secondary battery according to any one of claims 1-37, wherein, 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 134 mAh / g and less than or equal to 150 mAh / g.

39. The secondary battery according to any one of claims 1-38, wherein, The single-side coating weight of the positive electrode sheet is 300 mg / 1540 mm 2 - 580 mg / 1540 mm 2 .

40. The secondary battery according to any one of claims 1-39, wherein, The compacted density of the positive electrode plate is 2.25 g / cm 3 - 2.75 g / cm 3 .

41. An electrical device, comprising: The electric device comprises the secondary battery of any one of claims 1 to 40.

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