Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector. The positive electrode film layer comprises first-type particles and second-type particles, wherein the first-type particles and the second-type particles comprise a lithium-containing transition metal phosphate material. The primary particle size of the first-type particles is 50-180 nm; and the primary particle size of the second-type particles is greater than 180 nm and less than 900 nm. The average value of the molar ratio of Mn of the first-type particles is less than that of the molar ratio of Mn of the second-type particles, wherein the molar ratio of Mn refers to the proportion of the mole number of Mn to the total mole number of Mn and Fe.

Description

Secondary batteries and electrical appliances

[0001] Cross-references

[0002] This application incorporates Chinese Patent Application No. 202411035634.0, 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 more particularly 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 have a wide range of applications.

[0005] With the rapid development of electric vehicles and mobile electronic devices, the requirements for energy density and storage performance in rechargeable batteries are increasing. How to improve battery energy density while simultaneously maintaining good storage performance is a pressing technical problem 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 that combine high energy density and excellent storage performance.

[0007] The first aspect of this application provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte.

[0008] 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.

[0009] The positive electrode film layer includes first-type particles and second-type particles, both of which include lithium-containing transition metal phosphate materials.

[0010] The first type of particles has a primary particle size of 50nm-180nm; the second type of particles has a primary particle size greater than 180nm and less than 900nm.

[0011] The average molar percentage of Mn in the first type of particles is less than the average molar percentage of Mn in the second type of particles.

[0012] The Mn molar ratio refers to the proportion of the number of moles of Mn relative to the total number of moles of Mn and Fe.

[0013] The positive electrode active material comprises two types of particles with different primary particle sizes. This allows the particles of different sizes to cooperate and fill gaps, resulting in a denser particle packing in the positive electrode active material. This increases the powder compaction density and electrode compaction density, thereby improving the battery's energy density. However, the first type of particles has a larger specific surface area and higher surface activity, making them more prone to side reactions in the electrolyte and exacerbating manganese ion dissolution, thus affecting the battery's storage and cycle performance. This application reduces the likelihood of manganese dissolution during cycling and storage by controlling the average Mn molar ratio of the small-diameter, high-specific-surface-area first type of particles to be lower than the average Mn molar ratio of the second type of particles. This improves the powder compaction density and battery energy density while also enhancing the material's cycle and storage stability, and improving the battery's cycle and storage performance.

[0014] In any embodiment, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0%-12%, optionally 0%-8%, more preferably 0%-6%, and even more preferably 0%.

[0015] By controlling the molar percentage of Mn in the first type of particles within a suitable range, the side reactions between the small-diameter first type of particles and the electrolyte, as well as the degree of manganese dissolution, can be further reduced, thereby further improving the battery's storage and cycle performance. The battery is more suitable for application scenarios with high requirements for cycle life and / or storage life.

[0016] In any embodiment, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0.02%-12%, optionally 0.02%-8%, more preferably 0.02%-6%, and even more preferably 0.02%.

[0017] In any embodiment, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0.2%-12%, optionally 0.2%-8%, more preferably 0.2%-6%, and even more preferably 0.2%.

[0018] Controlling the molar percentage of Mn in the first type of particles within a suitable range ensures that the small-diameter first type of particles contain a certain amount of Mn. This allows the highly conductive first type of particles to fully utilize their specific capacity, further improving the energy density of the battery. As a result, the battery is more suitable for scenarios with high energy density requirements.

[0019] In any embodiment, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0-0.8, optionally 0-0.4, and more preferably 0.

[0020] By controlling the ratio of the average Mn molar percentage of the first type of particles to the average Mn molar percentage of the second type of particles within an appropriate range, the cycle stability and storage stability of the first type of particles can be improved, while the platform capacity contributed by the second type of particles can also be achieved, thus comprehensively improving the energy density and storage performance of the battery.

[0021] In any embodiment, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0.0003-0.8, optionally 0.0003-0.4, and more preferably 0.0003.

[0022] In any embodiment, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0.002-0.8, optionally 0.002-0.4, and more preferably 0.002.

[0023] By controlling the average value of the Mn molar ratio of the first type of particles and the average value of the Mn molar ratio of the second type of particles to be greater than 0, the first type of particles have a certain amount of Mn content. The first type of particles with excellent conductivity can give full play to their specific capacity, which is conducive to improving the energy density of the battery and making the battery more suitable for application scenarios with higher energy density requirements.

[0024] In any embodiment, the average Mn molar ratio of the second type of particles is 0.4-0.9, and can be optionally 0.5-0.9.

[0025] By controlling the average Mn molar ratio of the second type of particles within a suitable range, the second type of particles can have a high plateau capacity while also ensuring that the second type of particles have a certain conductivity. This is conducive to the second type of particles exerting their specific capacity, so that the second type of particles can contribute sufficient capacity, thereby improving the energy density of the battery.

[0026] In any embodiment, the average value of the Mn molar ratio of the first type of particles is 0-0.6, optionally 0-0.4, more preferably 0-0.2, and even more preferably 0.

[0027] Controlling the average Mn molar ratio of the first type of particles within a suitable range can reduce the possibility of side reactions between the first type of particles and the electrolyte, as well as the possibility of manganese dissolution, thereby improving the cycle stability and storage stability of the first type of particles and enhancing the cycle performance and storage performance of the battery.

[0028] In any embodiment, the average molar percentage of Mn in the first type of particles is 0.02-0.6, optionally 0.02-0.4, more preferably 0.02-0.2, and even more preferably 0.02.

[0029] In any embodiment, the average molar percentage of Mn in the first type of particles is 0.1-0.2, and can be selected as 0.1.

[0030] By controlling the average Mn molar ratio of the first type of particles within a suitable range, the cycle stability and storage stability of the first type of particles are improved, while also enabling the first type of particles to have a certain plateau capacity and specific capacity. This not only ensures that the battery has excellent cycle performance and storage performance, but also further improves the energy density of the battery.

[0031] In any embodiment, based on the total area of ​​the primary particles in the positive electrode film layer, the area ratio of the first type of particles is greater than 0% and less than or equal to 30%, which can be selected as 5%-20%; and / or, the area ratio of the second type of particles is greater than or equal to 70% and less than 100%, which can be selected as 80%-95%.

[0032] When the area ratio of the first type of particles and the second type of particles is within a suitable range, it is possible to achieve particle size distribution, improve the compaction density of the powder and the compaction density of the electrode, and at the same time, it can give full play to the purpose of providing platform capacity for the second type of particles with relatively high manganese content. It can also reduce the impact of the small-diameter first type of particles on the cycle performance and storage performance of the material, which is conducive to obtaining batteries with high energy density and excellent cycle performance and storage performance.

[0033] In any embodiment, the positive electrode film layer includes third-type particles, which include lithium-containing transition metal phosphate materials. The primary particle size of the third-type particles is greater than 900 nm and less than or equal to 5 μm.

[0034] Based on the total area of ​​primary particles in the positive electrode film layer, the area ratio of the third type of particles is greater than or equal to 5%.

[0035] Compared to the first and second types of particles, the third type of particles has a larger primary particle size. During cycling or storage, these particles are less likely to undergo side reactions with the electrolyte or experience manganese dissolution. The inclusion of this third type of particle, which exhibits excellent cycle and storage stability, in the positive electrode film further improves the cycle and storage stability of the positive electrode active material, thereby enhancing the battery's cycle and storage performance. Furthermore, the presence of three types of particles with different primary particle sizes in the positive electrode film allows for a large, medium, and small particle size distribution system, resulting in a denser packing and further increasing the electrode's compaction density. Additionally, the third type of particle has a higher specific capacity, leading to a higher energy density in the battery.

[0036] In any implementation, the average molar percentage of Mn in the third type of particles is less than the average molar percentage of Mn in the second type of particles.

[0037] As mentioned earlier, adding large-diameter third-type particles can further improve the cycle stability and storage stability of the material, which is beneficial for obtaining long-life batteries. However, the relatively large primary particle size of the third-type particles makes the migration path of lithium ions within the particles longer, resulting in increased discharge polarization of the third-type particles, affecting the kinetic performance of the material and the rate performance of the battery.

[0038] The molar ratio of Mn in particles affects their conductivity. By controlling the average molar ratio of Mn in the relatively large primary particle size third type of particles to be less than the average molar ratio of Mn in the relatively small primary particle size second type of particles, the conductivity of the relatively large primary particle size third type of particles can be improved, the discharge polarization of the third type of particles can be alleviated, and the kinetic performance of the material can be improved. This not only improves the storage stability of the material and the storage performance of the battery, but also improves the conductivity of the material and the rate performance of the battery, resulting in a battery with excellent storage and rate performance.

[0039] In any embodiment, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 0%-50%, optionally 0%-30%, more preferably 0%-10%, and even more preferably 0%.

[0040] Controlling the molar percentage of Mn in the third type of particles within a suitable range can further improve the conductivity of the third type of particles, alleviate the discharge polarization of the third type of particles, and help to further improve the rate performance of the battery.

[0041] In any embodiment, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 5%-50%, optionally 5%-30%, more preferably 5%-10%, and even more preferably 5%.

[0042] In any embodiment, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 10%-50%, optionally 10%-30%, and more preferably 10%.

[0043] Controlling the molar percentage of Mn in the third type of particles within a suitable range can alleviate the impact of excessive Mn concentration in the relatively small first and / or second type of particles on the cycle performance and storage performance of the battery. This can improve the energy density of the battery while also taking into account certain cycle performance and storage performance, making the battery more suitable for application scenarios with certain requirements for battery cycle life and / or storage life.

[0044] In any embodiment, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of M in the second type of particles is 0-0.8, optionally 0-0.5, and more preferably 0.

[0045] By controlling the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles within a suitable range, the conductivity of the third type of particles can be improved while also taking into account the high platform capacity contributed by the second type of particles, thus comprehensively improving the energy density and rate performance of the battery.

[0046] In any embodiment, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles is 0.0003-0.8, optionally 0.0003-0.5, and more preferably 0.0003.

[0047] In any embodiment, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles is 0.002-0.8, optionally 0.002-0.5, and more preferably 0.002.

[0048] By controlling the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles within a suitable range, the battery can achieve excellent rate performance, storage performance, and energy density.

[0049] In any embodiment, the average value of the Mn molar ratio of the third type of particles is 0-0.6, optionally 0-0.5, more preferably 0-0.1, and even more preferably 0.

[0050] Controlling the average molar ratio of Mn in the third type of particles within a suitable range can improve the conductivity of the third type of particles, enhance the overall conductivity of the material, and improve the rate performance of the battery.

[0051] In any embodiment, the average molar percentage of Mn in the third type of particles is 0.02-0.6, optionally 0.02-0.2, and more preferably 0.02.

[0052] In any embodiment, the average molar percentage of Mn in the third type of particles is 0.1-0.3, and can be selected as 0.1.

[0053] By controlling the average molar ratio of Mn in the third type of particles within a suitable range, the conductivity of the third type of particles and materials is improved, while also enabling the third type of particles to have a certain plateau capacity, thereby further improving the energy density of the battery.

[0054] In any implementation, based on the total area of ​​the primary particles in the positive electrode film layer, the area ratio of the first type of particles is 5%-15%, and / or the area ratio of the second type of particles is 45%-85%, and / or the area ratio of the third type of particles is 10%-40%.

[0055] By controlling the area ratio of particles of different sizes within a suitable range, the contribution of the high manganese content type II particles to the energy density in terms of both the average voltage and specific capacity can be achieved. At the same time, the impact of large-diameter type III particles on the rate performance of the battery and the impact of small-diameter type I particles on the cycle performance and storage performance of the battery can be reduced. The battery can achieve a balance of high energy density, good cycle performance, storage performance and rate performance.

[0056] In any embodiment, the average Mn molar ratio of the primary particles in the positive electrode film is 0.2-0.9, and can be selected as 0.4-0.8.

[0057] By controlling the average molar percentage of Mn in the overall particles within a suitable range, the material not only has high plateau capacity and specific capacity, but also excellent cycle stability, storage stability and high conductivity, which is beneficial for obtaining batteries with high energy density and excellent cycle performance, storage performance and rate performance.

[0058] In any embodiment, the particle size distribution index of the primary particle size of the second type of particles is greater than 0 and less than or equal to 0.5.

[0059] The particle size distribution index refers to the ratio of the standard deviation of the primary particle size of the second type of particles to the primary average particle size of the second type of particles.

[0060] By controlling the particle size distribution index of the primary particle size of the second type of particles within a suitable range, it is possible to improve the discharge behavior of each particle in the second type of particles during battery cycling, thereby reducing the possibility of overcharging and over-discharging during charging and discharging, which is beneficial to improving the structural stability of the material and further improving the cycle performance of the battery.

[0061] In any embodiment, the general formula of the lithium-containing transition metal phosphate material of the second type of particles includes Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0062] Wherein, 0.8≤m1≤1.2, x1≥0, y1>0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1, and / or,

[0063] The general formula for the composition of the first type of particles containing lithium transition metal phosphate materials includes Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 ,

[0064] Wherein, 0.8≤m²≤1.2, x²≥0, y²≥0, 0.9≤x²+y²≤1, 0.95≤z²≤1.1, 3.5≤n²≤4, 0≤a²≤0.1, 0≤b²≤0.1, 0≤c²≤0.1, 0≤d²≤0.1, and / or,

[0065] The general compositional formula of the third type of particle-containing lithium transition metal phosphate materials includes Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3 ,

[0066] 0.8≤m³≤1.2, x³≥0, y³≥0, 0.9≤x³+y³≤1, 0.95≤z³≤1.1, 3.5≤n³≤4, 0≤a³≤0.1, 0≤b³≤0.1, 0≤c³≤0.1, 0≤d³≤0.1

[0067] Among them, A1, A2, and A3 each independently include one or more of Al, Na, K, and Mg; M1, M2, and M3 each independently include one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q1, Q2, and Q3 each independently include one or more of B, S, Si, and N; and N1, N2, and N3 each independently include one or more of S, F, Cl, and Br.

[0068] In any embodiment, 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 2.35 g / cm³. 3-2.60g / cm 3 .

[0069] In any embodiment, the specific capacity of the positive electrode active material at 40°C and 1 / 3C discharge rate is 135mAh / g-150mAh / g.

[0070] In any embodiment, the positive electrode film layer further includes a binder and a conductive agent, wherein the mass ratio of the positive electrode active material, the binder and the conductive agent in the positive electrode film layer is (92-99):(0.5-3):(0.5-3).

[0071] In any embodiment, the areal density of the positive electrode film is 300 mg / 1540 mm². 2 -580mg / 1540mm 2 .

[0072] In any embodiment, the compaction density of the positive electrode film is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0073] A second aspect of this application provides an electrical device that includes the secondary battery of the first aspect. Attached Figure Description

[0074] Figure 1 is a longitudinal cross-sectional schematic diagram of the positive electrode sheet according to an embodiment of this application;

[0075] Figure 2 is a schematic diagram of the statistical distinction rules of primary particles in the transmission electron microscope image of particles in this application;

[0076] Figure 3 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0077] Figure 4 is an exploded view of the secondary battery according to an embodiment of this application shown in Figure 3;

[0078] Figure 5 is a schematic diagram of a battery module according to an embodiment of this application;

[0079] Figure 6 is a schematic diagram of a battery pack according to an embodiment of this application;

[0080] Figure 7 is an exploded view of the battery pack of one embodiment of this application shown in Figure 6;

[0081] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0082] Reference numerals: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 10 Positive electrode sheet; 110 Positive current collector; 120 Positive electrode film; 1210 Type I particles; 1220 Type II particles. Detailed Implementation

[0083] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. 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 making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0084] 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.

[0085] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0086] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0087] 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.

[0088] 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.

[0089] 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).

[0090] The cathode active material is one of the decisive factors in the performance of secondary batteries. Currently, common cathode active materials mainly include lithium cobalt oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, and lithium iron phosphate. Each of these materials has its advantages and disadvantages. For example, lithium cobalt oxide has high energy density and voltage plateau, but its cost is high and its safety is poor; lithium manganese oxide has lower cost and better safety, but its energy density and voltage plateau are lower; nickel-cobalt-manganese ternary materials combine the advantages of the former two, but their cost is still high. Lithium iron phosphate, on the other hand, has advantages such as low cost, high safety, and long lifespan, which can better meet the requirements of the new energy vehicle market for high safety and low cost of lithium-ion batteries. However, lithium iron phosphate also has some disadvantages, such as low powder compaction density and low discharge capacity, which limit its application in high-energy-density batteries. Lithium manganese iron phosphate, as a new material for the further development of lithium iron phosphate, combines the advantages of manganese and iron, and has two voltage plateaus at 4.1V and 3.4V respectively, which can provide a certain plateau capacity and is expected to improve the shortcomings of lithium iron phosphate materials. However, in current research and applications, lithium manganese iron phosphate (LFP) still suffers from low compaction density and has not yet demonstrated its potential advantage of high energy density. Furthermore, the trivalent manganese ions in LFP exhibit the Jan Taylor effect, transforming into tetravalent manganese ions. These highly reactive tetravalent manganese ions readily react with the electrolyte to become divalent manganese ions. These divalent manganese ions further dissolve in the electrolyte and are reduced and precipitated at the negative electrode, damaging the SEI film. This results in more active lithium being consumed during SEI film repair, thus affecting the battery's storage life. Therefore, how to improve the compaction density of LFP powder to obtain high-energy-density batteries while simultaneously maintaining good storage performance has become a key research focus.

[0091] [Rechargeable Battery]

[0092] Based on this, this application proposes a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte.

[0093] 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.

[0094] The positive electrode film layer comprises a first type of particles and a second type of particles, wherein the first type of particles and the second type of particles comprise lithium-containing transition metal phosphate materials.

[0095] The first type of particles has a primary particle size of 50nm-180nm; the second type of particles has a primary particle size greater than 180nm and less than 900nm.

[0096] The average molar percentage of Mn in the first type of particles is less than the average molar percentage of Mn in the second type of particles.

[0097] 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.

[0098] 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 first type particles 1210 and second type particles 1220.

[0099] In this paper, the term "primary particle size" refers to the particle size of a primary particle.

[0100] Primary particles refer to individual particles that can be distinguished after being identified by general-purpose software (e.g., SpectrumSee; Avizo 3D) in transmission electron microscopy (TEM) images, and / or individual particles that can be distinguished after manual identification or manual-assisted calibration. Specifically, in this paper, to identify primary particles, the particles contained in the positive electrode film were enriched and / or dispersed, and then imaged under a TEM. The resulting images can be directly identified using software (based on parameters such as grayscale and / or contrast / brightness), and the individual particles that are distinguished after identification are primary particles. Alternatively, the images can be directly identified manually, and the individual particles that are distinguished after identification are primary particles. Another method is to directly identify the images using a combination of software and manual calibration, and the individual particles that are identified and confirmed to be distinguishable are primary particles. More specifically, particles that form independent, clearly distinguishable boundaries in the TEM field of view can be directly identified as individual particles through software or manual identification. However, some particles, although dispersed, exhibit a certain degree of adhesion and stacking in the TEM field of view. For particles that are stuck together or stacked, those identified as individual particles by software (based on parameters such as grayscale / contrast / brightness) are counted as first-order particles. For more precise analysis, for particles that are stuck together or stacked to some extent under a transmission electron microscope (TEM) field of view, after being identified as individual particles by software based on parameters such as grayscale / contrast / brightness, potentially misidentified particles are manually calibrated according to certain rules. The calibrated, distinguishable individual particles are then counted as first-order particles. If there are inconsistencies in the manual calibration results, 3, 5, or 7 people, unaware of each other's knowledge of the same imaging result, can individually calibrate according to the rules illustrated below. The results are then statistically calculated, and the result obtained in this way is counted as the number of first-order particles. Figure 2 is a schematic diagram of the statistical distinction rules for primary particles in a transmission electron microscope (TEM) image. 2-a is the original TEM image, 2-b is the software-recognized image, and 2-c is an example of software and / or manual identification of independent, adhered, and stacked particles in 2-a. Particles 1 and 2 are distinguishable independent particles, designated as primary particles 1 and 2, respectively. Particles 3 and 4 in 2-c are adhered; particles 5, 6, and 7 are also adhered, and after software or manual identification, they are determined to be primary particles 3, 4, 5, 6, and 7, respectively. Particles 8 and 9, which are stacked together, are ultimately identified as primary particles 8 and 9, rather than being classified as a single particle. Figure 2-d is another example of software and / or manual identification of stacked particles in 2-a. Particles 10-14, which are stacked together, are ultimately identified as primary particles 10, 11, 12, 13, and 14, rather than the entire stack of particles being classified 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.

[0101] The average value of the Mn molar ratio of the first type of particles and the average value of the Mn molar ratio of the second type of 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 the binder and dispersant 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 molar content of Mn and Fe in each effective particle in the transmission electron microscope (TEM) image. This allows calculation of 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 of the transmission surface of each particle. Multiple TEM and EDS tests are performed in different test areas, testing the cross-sectional area S, primary particle size d, and molar percentage of Mn X of at least 500 effective particles. The obtained effective particles are then numbered from smallest to largest primary particle size as 1, 2, 3, 4, 5…n, for a total of n particles. The m-th particle has a primary diameter less than or equal to 180 nm, the (m+1)-th particle has a primary diameter greater than 180 nm, the (k-1)-th particle has a primary diameter less than 900 nm, and the k-th particle has a primary diameter greater than or equal to 900 nm. Therefore, particles 1 to m are classified as Class I particles, and particles (m+1) to (k-1)-th particles are classified as Class II particles. When the primary diameter of particle n is less than 900 nm, i.e., particles 1 to m are Class I particles, and particles (m+1) to n are Class II particles, then k-1 is n.

[0102] The formula for calculating the average molar percentage of Mn in the first type of particles is as follows:

[0103] The formula for calculating the average molar percentage of Mn in the second type of particles is as follows:

[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] The positive electrode active material comprises two types of particles with different primary particle sizes. This allows the particles of different sizes to work together to fill gaps, resulting in a denser particle packing and increased powder compaction density and electrode compaction density, thereby improving the battery's energy density. However, the smaller-sized first-type particles have a larger specific surface area and higher surface activity, making them more susceptible to side reactions in the electrolyte and exacerbating manganese ion dissolution, thus affecting the battery's cycle performance and storage performance. This application reduces the likelihood of manganese dissolution during cycling and storage by controlling the average Mn molar ratio of the smaller-sized, higher-specific-surface-area first-type particles to be lower than the average Mn molar ratio of the second-type particles. This improves the material's cycle stability and storage stability, enhancing the battery's cycle and storage performance. Simultaneously, the larger-sized, lower-specific-surface-area second-type particles have a relatively higher Mn molar ratio, which, while maintaining good cycle and storage stability, increases the plateau capacity and specific capacity of the second-type particles, contributing to higher battery energy density.

[0106] In summary, the positive electrode film contains first-type particles with a primary particle size of 50nm-180nm and second-type particles with a primary particle size greater than 180nm and less than 900nm. Furthermore, the average molar ratio of Mn in the first-type particles with relatively high reactivity is lower than the average molar ratio of Mn in the second-type particles with relatively low reactivity. This can improve the powder compaction density of the material and the energy density of the battery, while also reducing the possibility of manganese dissolution and improving the cycle performance and storage performance of the battery.

[0107] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0%-12%, optionally 0%-8%, more preferably 0%-6%, and even more preferably 0%.

[0108] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles can be selected as 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or any range between any two of the above values.

[0109] Based on the total number of moles of Mn in the primary particles of the positive electrode film, the test method for the molar percentage of Mn in the first type of particles can be performed using methods and equipment known in the art, as exemplified below: referring to the aforementioned test method for measuring the average molar percentage of Mn in the first type of particles, the cross-sectional area S and the molar percentage X of Mn for each particle are determined.

[0110] Based on the total number of moles of Mn in the primary particles of the positive electrode film, the formula for calculating the molar percentage of Mn in the first type of particles is:

[0111] 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.

[0112] By controlling the molar percentage of Mn in the first type of particles within a suitable range, the side reactions between the small-diameter first type of particles and the electrolyte, as well as the degree of manganese dissolution, can be further reduced, thereby further improving the cycle performance and storage performance of the battery. The battery is suitable for application scenarios with high requirements for cycle performance and / or storage performance.

[0113] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0.02%-12%, optionally 0.02%-8%, more preferably 0.02%-6%, and even more preferably 0.02%.

[0114] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles can be optionally 0.02%, 0.03%, 0.04%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or a range between any two of the above values.

[0115] Controlling the molar percentage of Mn in the first type of particles within a suitable range allows the small-diameter first type of particles to have a small amount of Mn, which is beneficial for the highly conductive first type of particles to fully utilize their specific capacity, thereby improving the energy density of the battery. This makes the battery more suitable for scenarios with certain energy density requirements.

[0116] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0.2%-12%, optionally 0.2%-8%, more preferably 0.2%-6%, and even more preferably 0.2%.

[0117] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles can be optionally 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, or any range between any two of the above values.

[0118] Controlling the molar percentage of Mn in the first type of particles within a suitable range allows the small-diameter first type of particles to have a certain amount of Mn, which is beneficial for the highly conductive first type of particles to fully utilize their specific capacity, thereby further improving the energy density of the battery. This makes the battery more suitable for scenarios with high energy density requirements.

[0119] In some embodiments, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0-0.8, optionally 0-0.4, and more preferably 0.

[0120] In some embodiments, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles can be selected as 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, or 0. 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 between any two of the above values.

[0121] By controlling the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles within an appropriate range, the cycle stability and storage stability of the first type of particles can be improved, while the platform capacity contributed by the second type of particles can also be achieved, thus comprehensively improving the energy density, cycle performance and storage performance of the battery.

[0122] In some embodiments, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0.0003-0.8, optionally 0.0003-0.4, and more preferably 0.0003.

[0123] In some embodiments, the ratio of the average Mn molar percentage of the first type of particles to the average Mn molar percentage of the third type of particles can be selected as 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, or 0.00 7, 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 between any two of the above values.

[0124] By controlling the average Mn molar ratio of the first type of particles and the average Mn molar ratio of the second type of particles within a suitable range, the first type of particles, which contain a small amount of Mn and have excellent conductivity, can fully utilize their specific capacity, which is beneficial to improving the energy density of the battery and making the battery more suitable for application scenarios with certain energy density requirements.

[0125] In some embodiments, the ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0.002-0.8, optionally 0.002-0.4, and more preferably 0.002.

[0126] In some embodiments, the ratio of the average Mn molar percentage of the first type of particles to the average Mn molar percentage of the third type of particles can be selected as 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any range between the above two values.

[0127] By controlling the average Mn molar ratio of the first type of particles and the average Mn molar ratio of the second type of particles within a suitable range, the first type of particles can have a certain amount of Mn content. The first type of particles with excellent conductivity can fully exert their specific capacity, which is beneficial to improving the energy density of the battery and making the battery more suitable for application scenarios with high energy density requirements.

[0128] In some embodiments, the average molar percentage of Mn in the second type of particles is 0.4-0.9, and optionally 0.5-0.9.

[0129] In some embodiments, the average value of the molar percentage of Mn in the second type of particles can be selected as 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or any range between any two of the above values.

[0130] By controlling the average Mn molar ratio of the second type of particles within a suitable range, the second type of particles can have a high plateau capacity while also ensuring that the second type of particles have a certain conductivity. This is conducive to the second type of particles exerting their specific capacity, so that the second type of particles can contribute sufficient capacity, thereby improving the energy density of the battery.

[0131] In some embodiments, the average Mn molar ratio of the first type of particles is 0-0.6, optionally 0-0.4, more preferably 0-0.2, and even more preferably 0. In some embodiments, the average value of the Mn molar ratio of the first type of particles can be selected as 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range between any two of the above values.

[0132] Controlling the average Mn molar ratio of the first type of particles within a suitable range can reduce the possibility of side reactions between the first type of particles and the electrolyte, as well as the possibility of manganese dissolution. This can improve the cycle stability and storage stability of the first type of particles, enhance the cycle performance and storage performance of the battery, and extend the cycle life and storage life of the battery.

[0133] In some embodiments, the average molar ratio of Mn in the first type of particles is 0.02-0.6, optionally 0.02-0.4, more preferably 0.02-0.2, and even more preferably 0.02.

[0134] In some embodiments, the average value of the Mn molar ratio of the first type of particles can be selected as 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range between any two of the above values.

[0135] By controlling the average molar ratio of Mn in the first type of particles within a suitable range, the cycle stability and storage stability of the first type of particles are improved, while also enabling the first type of particles to have a certain specific capacity. This allows the first type of particles with excellent conductivity to fully utilize their specific capacity, which is beneficial to improving the energy density of the battery.

[0136] In some embodiments, the average molar percentage of Mn in the first type of particles is 0.1-0.2, and can be selected as 0.1.

[0137] In some embodiments, the average value of the Mn molar ratio of the first type of particles can be selected as 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, or any range between any two of the above values.

[0138] By controlling the average Mn molar ratio of the first type of particles within a suitable range, the first type of particles not only have certain cycle stability and storage stability, but also have high plateau voltage and specific capacity. This allows the first type of particles with excellent conductivity to fully utilize their specific capacity, which is beneficial to further improving the energy density of the battery.

[0139] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the first type of particles is greater than 0% and less than or equal to 30%, optionally 5%-20%; and / or, the area percentage of the second type of particles is greater than or equal to 70% and less than 100%, optionally 80%-95%.

[0140] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the first type of particles can be selected as 0.5%, 1%, 2%, 5%, 7%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 27%, 30%, or any range between any two of the above values.

[0141] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the second type of particles can be selected as 80%, 81%, 82%, 85%, 87%, 90%, 92%, 95%, 98%, 99%, 99.5%, or any range between any two of the above values.

[0142] The method for testing the area ratio of the first type of particles and the area ratio of the second type of particles can be performed using methods and equipment known in the art, as exemplified below: Referring to the aforementioned method for testing the average value of the Mn molar ratio of the second type of particles, the cross-sectional area S of each particle is determined.

[0143] The formula for calculating the area ratio of the first type of particles is:

[0144] The formula for calculating the area ratio of the second type of particles is:

[0145] Where Si and Sj represent the cross-sectional areas of particles numbered i and j, respectively.

[0146] When the area ratio of the first type of particles and the second type of particles is within a suitable range, it can achieve particle size distribution, improve the powder compaction density and electrode compaction density of the material, and at the same time, it can give full play to the purpose of providing platform capacity for the second type of particles with relatively high manganese content. It can also reduce the impact of small-diameter first type of particles on the cycle stability and storage stability of the material, which is conducive to obtaining batteries with high energy density and excellent cycle performance and storage performance.

[0147] In some embodiments, the positive electrode film layer includes a third type of particles, which includes the lithium-containing transition metal phosphate material, wherein the primary particle size of the third type of particles is greater than 900 nm and less than or equal to 5 μm.

[0148] Based on the total area of ​​the primary particles in the positive electrode film layer, the area ratio of the third type of particles is greater than or equal to 5%.

[0149] The determination of the third type of particles and the test method for their area proportion can be carried out using methods and equipment known in the art, as exemplified below: Referring to the aforementioned test method for the average value of the Mn molar proportion of the first type of particles, the kth to nth particles are defined as the third type of particles. The formula for calculating the area proportion of the third type of particles is:

[0150] Where Xi represents the molar percentage of Mn in particle number i, and Si represents the cross-sectional area of ​​particle number i.

[0151] Compared to the first and second types of particles, the third type of particles has a larger primary particle size. During cycling or storage, these particles are less likely to undergo side reactions with the electrolyte or experience manganese dissolution. The inclusion of this third type of particle, which exhibits excellent cycle and storage stability, in the positive electrode film further improves the cycle and storage stability of the positive electrode active material, thereby enhancing the battery's cycle and storage performance. Furthermore, the presence of three types of particles with different primary particle sizes in the positive electrode film allows for a large, medium, and small particle size distribution system, resulting in a denser packing and further increasing the electrode's compaction density. Additionally, the third type of particle has a higher specific capacity, leading to a higher energy density in the battery.

[0152] In some embodiments, the average molar percentage of Mn in the third type of particles is less than the average molar percentage of Mn in the second type of particles.

[0153] The test method for the average Mn molar ratio of the third type of particles is the same as the test method for the average Mn molar ratio of the first type of particles.

[0154] The formula for calculating the average molar percentage of Mn in the third type of particles is as follows:

[0155] Where Xi represents the molar percentage of Mn in particle number i, and Si represents the cross-sectional area of ​​particle number i.

[0156] As mentioned earlier, the addition of large-diameter third-type particles can further improve the cycle stability and storage stability of the material, which is beneficial to obtaining a long-life battery. However, the relatively large primary particle size of the third-type particles makes the migration path of lithium ions within the particles longer, resulting in increased discharge polarization of the third-type particles, affecting the kinetic performance of the material and the rate performance of the battery.

[0157] The molar ratio of Mn in particles affects their conductivity. By controlling the average molar ratio of Mn in the relatively large primary particle size third type of particles to be less than the average molar ratio of Mn in the relatively small primary particle size second type of particles, the conductivity of the relatively large primary particle size third type of particles can be improved, the discharge polarization of the third type of particles can be alleviated, and the kinetic performance of the material can be improved. This not only improves the storage stability of the material and the storage performance of the battery, but also improves the conductivity of the material and the rate performance of the battery, resulting in a battery with excellent storage and rate performance.

[0158] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 0%-50%, optionally 0%-30%, more preferably 0%-10%, and even more preferably 0%.

[0159] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%. %, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or a range between any two of the above values.

[0160] Based on the total number of moles of Mn in the primary particles of the positive electrode film, the test method for the molar percentage of Mn in the third type of particles can be performed using methods and equipment known in the art, as exemplified below: Referring to the aforementioned test method for determining the average molar percentage of Mn in the third type of particles, the cross-sectional area S and the molar percentage X of Mn for each particle are determined.

[0161] Based on the total number of moles of Mn in the primary particles of the positive electrode film, the formula for calculating the molar percentage of Mn in the third type of particles is as follows:

[0162] 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.

[0163] Controlling the molar percentage of Mn in the third type of particles within a suitable range can further improve the conductivity of the third type of particles, alleviate the discharge polarization of the third type of particles, and help to further improve the rate performance of the battery.

[0164] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 5%-50%, optionally 5%-30%, more preferably 5%-10%, and even more preferably 5%.

[0165] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles can be selected as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any range between any two of the above values.

[0166] The presence of a small amount of Mn in the third type of particles can alleviate the impact of excessive Mn concentration in the relatively small first or second type of particles on the cycle performance and storage performance of the battery. This not only improves the energy density of the battery but also enhances its cycle performance and storage performance, making the battery more suitable for applications with certain requirements for cycle life and / or storage life.

[0167] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles is 10%-50%, optionally 10%-30%, and more preferably 10%.

[0168] In some embodiments, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the third type of particles can be selected as 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any range between any two of the above values.

[0169] The distribution of a certain amount of Mn in the third type of particles can alleviate the impact of excessive Mn concentration in the relatively small first or second type of particles on the cycle performance and storage performance of the battery. While improving the energy density of the battery, it can also improve the cycle performance and storage performance of the battery, making the battery more suitable for application scenarios with high requirements for cycle life and / or storage life.

[0170] In some embodiments, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of M in the second type of particles is 0-0.8, optionally 0-0.5, and more preferably 0.

[0171] In some embodiments, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of M in the second type of particles is 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.00 6, 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 between any two of the above values.

[0172] By controlling the ratio of the average Mn molar percentage of the third type of particles to the average Mn molar percentage of the second type of particles within a suitable range, the structural stability of the third type of particles can be improved while also taking into account the high platform capacity contributed by the second type of particles, thus comprehensively improving the energy density and storage performance of the battery.

[0173] In some embodiments, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles is 0.0003-0.8, optionally 0.0003-0.5, and more preferably 0.0003.

[0174] In some embodiments, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of M in the second type of particles can be selected as 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, or 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 between any two of the above values.

[0175] Controlling the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles to be greater than 0 can alleviate the impact of excessive Mn concentration in the relatively small second type of particles on the cycle performance and storage performance of the battery, making the battery more suitable for application scenarios with certain requirements for cycle life and / or storage life.

[0176] In some embodiments, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles is 0.002-0.8, optionally 0.002-0.5, and more preferably 0.002.

[0177] In some embodiments, the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of M in the second type of particles can be selected as 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any range between the above two values.

[0178] Controlling the ratio of the average molar percentage of Mn in the third type of particles to the average molar percentage of Mn in the second type of particles within a suitable range can alleviate the impact of excessive Mn concentration in the relatively small second or first type of particles on the cycle performance and storage performance of the battery, making the battery more suitable for applications with high requirements for cycle life and / or storage life.

[0179] In some embodiments, the average Mn molar percentage of the third type of particles is 0-0.6, optionally 0-0.5, optionally 0-0.1, and further optionally 0.

[0180] In some embodiments, the average value of the Mn molar percentage of the third type of particles can be selected as 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range between any two of the above values.

[0181] Controlling the average molar ratio of Mn in the third type of particles within a suitable range can improve the conductivity of the third type of particles, enhance the overall conductivity of the material, and improve the rate performance of the battery.

[0182] In some implementations, the average molar percentage of Mn in the third type of particles is 0.02-0.6, optionally 0.02-0.2, and more preferably 0.02.

[0183] In some embodiments, the average value of the Mn molar percentage of the third type of particles can be selected as 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or any range between any two of the above values.

[0184] By controlling the average Mn molar ratio of the third type of particles to be greater than 0, the conductivity of the third type of particles and materials is improved, and the third type of particles also have a certain plateau capacity, which can further improve the energy density of the battery.

[0185] In some implementations, the average molar percentage of Mn in the third type of particles is 0.1-0.3, and can be selected as 0.1.

[0186] In some embodiments, the average value of the Mn molar percentage of the third type of particles can be selected as 0.1, 0.12, 0.14, 0.15, 0.18, 0.20, 0.22, 0.24, 0.25, 0.28, 0.30, or any range between any two of the above values.

[0187] By controlling the average Mn molar ratio of the third type of particles within a suitable range, the conductivity of the third type of particles and materials can be improved, while also enabling the third type of particles to have a certain voltage plateau and plateau capacity. This can further improve the energy density of the battery, making it more suitable for applications with high energy density requirements.

[0188] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area ratio of the first type of particles is 5%-15%, and / or the area ratio of the second type of particles is 45%-85%, and / or the area ratio of the third type of particles is 10%-40%.

[0189] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the first type of particles is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any two of the above values.

[0190] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the second type of particles is 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, or a range between any two of the above values.

[0191] In some embodiments, based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the third type of particles is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any range between any two of the above values.

[0192] By controlling the area ratio of particles of different sizes within a suitable range, the contribution of the high manganese content type II particles to the energy density in terms of both the average voltage and specific capacity can be achieved. At the same time, the impact of large-diameter type III particles on the rate performance of the battery and the impact of small-diameter type I particles on the cycle performance and storage performance of the battery can be reduced. The battery can achieve a balance of high energy density, good cycle performance, storage performance and rate performance.

[0193] In some embodiments, the average Mn molar ratio of the primary particles in the positive electrode film is 0.2-0.9, and optionally 0.4-0.8.

[0194] In some embodiments, the average value of the Mn molar ratio of the primary particles in the positive electrode film can be selected as 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, 0.85, 0.90, or any range between any two of the above values.

[0195] The average Mn molar percentage of the primary particles in the positive electrode film can be determined using methods and equipment known in the art, as exemplified below: Referring to the aforementioned test method for testing the average Mn molar percentage of the second type of particles, the cross-sectional area S and the Mn molar percentage X of each particle are determined.

[0196] The formula for calculating the average molar percentage of Mn in the primary particles of the positive electrode film is as follows:

[0197] Where Xi represents the molar percentage of Mn in particle number i, and Si represents the cross-sectional area of ​​particle number i.

[0198] By controlling the molar ratio of Mn in the overall particles within a suitable range, the material not only has a high plateau capacity, but also excellent cycle stability, storage stability, and conductivity, which is beneficial for obtaining batteries with high energy density and excellent cycle performance, storage performance, and rate performance.

[0199] In some embodiments, the primary particle size distribution index of the second type of particles is greater than 0 and less than or equal to 0.5.

[0200] The particle size distribution index refers to the ratio of the standard deviation of the primary particle size of the second type of particles to the primary average particle size of the second type of particles.

[0201] In some embodiments, the particle size distribution index of the primary particle size of the second type of particles can be selected as 0.01, 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, or a range between any two of the above values.

[0202] The test method for the particle size distribution index of the primary particle size of the second type of particles is carried out using methods and equipment known in the art, as exemplified below: The primary particle size of each particle in the second type of particles is determined by referring to the aforementioned test method for measuring the average value of the Mn molar ratio of the second type of particles.

[0203] Particle size distribution index (PDI) is the standard deviation of particle size σ divided by the average particle size.

[0204] Where σ is the standard deviation of particle size, x i This represents the primary particle size of each particle in the second type of particles. Let n be the first-order average particle size of the second type of particles, and n be the total number of second-type particles in the statistics. The average particle size is the total first-order particle size value of the second type of particles divided by the total number of second-type particles in the statistics.

[0205] By controlling the particle size distribution index of the primary particle size of the second type of particles within a suitable range, it is possible to improve the discharge behavior of each particle in the second type of particles during battery cycling, thereby reducing the possibility of overcharging and over-discharging during charging and discharging, which is beneficial to improving the structural stability of the material and further improving the cycle performance of the battery.

[0206] In some embodiments, the general formula of the lithium transition metal phosphate material of the second type of particles includes Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0207] Wherein, 0.8≤m1≤1.2, x1≥0, y1>0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1, and / or,

[0208] The general formula of the lithium-containing transition metal phosphate material of the first type of particles includes Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 ,

[0209] Wherein, 0.8≤m²≤1.2, x²≥0, y²≥0, 0.9≤x²+y²≤1, 0.95≤z²≤1.1, 3.5≤n²≤4, 0≤a²≤0.1, 0≤b²≤0.1, 0≤c²≤0.1, 0≤d²≤0.1, and / or,

[0210] The general formula of the lithium-containing transition metal phosphate material of the third type of particles includes Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3 ,

[0211] 0.8≤m³≤1.2, x³≥0, y³≥0, 0.9≤x³+y³≤1, 0.95≤z³≤1.1, 3.5≤n³≤4, 0≤a³≤0.1, 0≤b³≤0.1, 0≤c³≤0.1, 0≤d³≤0.1

[0212] Among them, A1, A2, and A3 each independently include one or more of Al, Na, K, and Mg; M1, M2, and M3 each independently include one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, and Ti; Q1, Q2, and Q3 each independently include one or more of B, S, Si, and N; and N1, N2, and N3 each independently include one or more of S, F, Cl, and Br.

[0213] 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.

[0214] 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.

[0215] 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.

[0216] 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.

[0217] 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.

[0218] 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, increase the energy density of the battery, and reduce interfacial side reactions between the material and the electrolyte during use, thereby improving the cycle performance and storage performance of the material.

[0219] 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.

[0220] Choosing appropriate modifying elements A1, A2, and A3 can also improve the lattice change rate of the material and maintain its battery capacity.

[0221] Modifying elements N1, N2, and N3 can help improve interfacial side reactions between the material and the electrolyte, reduce interfacial activity, and thus improve the cycle performance of the positive electrode active material. Furthermore, it can enhance the material's resistance to acid corrosion such as HF, thereby improving its cycle performance and storage life.

[0222] 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.

[0223] In some embodiments, the positive electrode film layer comprises a positive electrode active material, which includes the lithium-containing transition metal phosphate material, and the powder compaction density of the positive electrode active material at a pressure of 29400 N is 2.35 g / cm³. 3 -2.60g / cm 3 .

[0224] In some embodiments, the compacted density of the positive electrode active material at a pressure of 29400 N is 2.35 g / cm³. 3 2.36 g / cm 3 2.37 g / cm 3 2.38g / cm 3 2.39 g / cm 3 2.40 g / cm 3 2.41 g / cm 3 2.42 g / cm 3 2.43 g / cm 3 2.44 g / cm 3 2.45g / cm 3 2.46 g / cm 3 2.47 g / cm 3 2.48 g / cm 3 2.49 g / cm 3 2.50g / cm 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 32.54 g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.60g / cm 3 , or the range between any two of the above values.

[0225] The compaction density of the positive electrode active material powder at 29400N pressure can be determined using methods and equipment known in the art, as exemplified below: 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 and thoroughly washed with acetone to remove the binder from the positive electrode film. The powder is then dried 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 center 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. The compaction density of the material is then ρ = m / v, where v = (S × H), m is the mass of the powder, S is the bottom area of ​​the mold, and H is the thickness of the powder after compaction. The compaction density instrument model is UTM7305; the manufacturer is Sansi Zongheng.

[0226] The higher the powder compaction density, the higher the mass of powder material per unit volume. When the powder compaction density of the material is within a suitable range, the positive electrode sheet has a higher compaction density during cold pressing, which is beneficial to further improve the volumetric energy density of the battery.

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

[0228] The specific capacity of the positive electrode active material can be determined using methods and equipment known in the art, for example as follows: Place the battery in a 40°C oven environment and let it stand for 2 hours to maintain the battery temperature at 40°C; then discharge the battery at a constant current of 1 / 3C to 2.0V; let it stand 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; let it stand for 5 minutes; and then discharge the battery at a constant current of 1 / 3C to 2.0V to obtain the discharge capacity C of the battery. Disassemble the battery to obtain a positive electrode sheet with a total area of ​​S1. Cut the positive electrode sheet to obtain a positive electrode sheet with an area of ​​S2. After peeling the positive electrode film layer on the positive electrode sheet from the current collector, dissolve it in acetone, wash thoroughly to remove residual solvent, binder, dispersant, etc., and then filter and dry to obtain sample powder. The weight of the sample powder is M2. Then the total mass M1 of the positive electrode active material of the battery is approximately M2*(S1 / S2). The specific capacity of the positive electrode active material = the discharge capacity C of the battery / the mass M1 of the positive electrode active material.

[0229] [Preparation method of positive electrode active material]

[0230] This application also provides a method for preparing a positive electrode active material:

[0231] The first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material are mixed to obtain the positive electrode active material.

[0232] The first lithium-containing transition metal phosphate material comprises a first core and a first carbon coating layer covering the outer surface of the first core, and the second lithium-containing transition metal phosphate material comprises a second core and a second carbon coating layer covering the outer surface of the second core.

[0233] The primary average particle size of the first lithium-containing transition metal phosphate material is smaller than that of the second lithium-containing transition metal phosphate material.

[0234] The molar percentage of Mn in the first lithium-containing transition metal phosphate material is less than that in the second lithium-containing transition metal phosphate material.

[0235] The primary average particle size of the first lithium-containing transition metal phosphate material is 50 nm to 200 nm.

[0236] The primary average particle size of the second lithium-containing transition metal phosphate material is 120 nm-600 nm.

[0237] The Mn molar ratio refers to the proportion of the number of moles of Mn relative to the total number of moles of Mn and Fe.

[0238] The test method for the molar content of Mn in the first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material can be carried out using methods and equipment known in the art. For example, the molar content of Mn and Fe elements can be tested by referring to the chemical analysis method for nano-lithium iron phosphate in national standard GB T33822-2017, and the molar content of Mn can be calculated.

[0239] The method for testing the primary average particle size of the first and second lithium-containing transition metal phosphate materials can be carried out using methods and equipment known in the art, as exemplified below: 0.05 g of the test material is dissolved in 40 ml of anhydrous ethanol, and then an appropriate amount of dispersant is added and stirred evenly to obtain a suspension. 2 ml of the suspension and 2 ml of anhydrous ethanol are mixed and ultrasonically treated with an ultrasonic power of 480 W for 5 min to obtain a uniformly dispersed suspension. An appropriate amount of the intermediate suspension is then subjected to transmission electron microscopy (TEM). Referring to the aforementioned definition of primary particles, the projection area of ​​each primary particle in the TEM image is calculated, which is the cross-sectional area S of the primary particle. The equivalent circle diameter of the primary particle is obtained using the equivalent circle method, which is the primary particle diameter d. In the above statistical process of primary particles and their primary particle diameters, primary particles with a primary particle diameter less than 50 nm are not included in the statistical range (i.e., primary particles with a primary particle diameter greater than or equal to 50 nm are considered valid particles). The cross-sectional area S and primary particle size d of at least 500 effective particles are tested. The average primary particle size of the material under test is equal to the sum of the primary particle sizes of all primary particles and the total number of primary particles.

[0240] In some embodiments, the molar percentage of Mn in the first lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.4, more preferably 0-0.2, and even more preferably 0.

[0241] In some embodiments, the molar ratio of Mn in the first lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.4, more preferably 0.02-0.2, and even more preferably 0.02.

[0242] In some embodiments, the molar ratio of Mn in the first lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.4, and more preferably 0.2.

[0243] In some embodiments, the molar percentage of Mn in the second lithium-containing transition metal phosphate material is 0.4-0.9, and optionally 0.5-0.9.

[0244] In some embodiments, the primary particles with a primary particle size of 50nm-180nm in the second lithium transition metal phosphate material have a particle size distribution of less than or equal to 10%, optionally less than or equal to 8.5%, and more preferably 1%-6%.

[0245] Primary particles with a primary diameter greater than or equal to 1200 nm occupy 250 μm of the longitudinal section of the electrode prepared from the second lithium-containing transition metal phosphate material. 2 The number of particles in the region is less than or equal to 15, can be less than or equal to 12, or can be 1-8.

[0246] The particle size distribution of primary particles with a primary diameter of 50 nm to 180 nm in a material can be tested using methods and equipment known in the art. For example, the primary diameter of each primary particle in the sample material is obtained by referring to the aforementioned method for testing the average primary diameter of the sample material. The number of primary particles with a primary diameter of 50 nm to 180 nm is denoted as M, and the total number of primary particles is N (including particles with a primary diameter greater than or equal to 50 nm). The particle size distribution of primary particles with a primary diameter of 50 nm to 180 nm in the material is M / N*100%.

[0247] The method for testing the number of primary particles with a primary diameter greater than or equal to 1200 nm in a 250 μm² region of the longitudinal section of the electrode prepared from the material can be performed using methods and equipment known in the art. An example is as follows: An electrode is prepared by mixing the material to be tested with polyvinylidene fluoride (PVDF) binder at a mass ratio of 95:5. An argon ion beam is used to cut the electrode perpendicular to its large surface, exposing the entire longitudinal section. The entire longitudinal section is photographed using a scanning electron microscope (SEM). The projection area of ​​each primary particle, i.e., the cross-sectional area S of the primary particle, can be calculated using Avizo 3D image processing software. The equivalent circle diameter of the primary particle is obtained using the equivalent circle method. A test area of ​​250 μm² is randomly selected, and the number of primary particles with a primary diameter greater than or equal to 1200 nm within this test area is counted. During testing, 10 test areas can be randomly selected from different regions of the longitudinal section of the electrode for testing, and the average value is taken.

[0248] In some embodiments, the particle size distribution index of the primary particles with a primary particle size greater than 180 nm and less than 1200 nm in the second lithium-containing transition metal phosphate material is less than or equal to 0.45, optionally less than or equal to 0.36, and more preferably 0.20-0.30.

[0249] The particle size distribution index of primary particles with a primary diameter greater than 180 nm and less than 1200 nm in a material can be determined using methods and equipment known in the art. For example: referring to the aforementioned method for testing the average primary particle size of sample materials, the primary particle size of the sample to be tested is obtained. Primary particles with a primary diameter greater than 180 nm and less than 1200 nm are denoted as statistical particles.

[0250] Particle size distribution index (PDI) is the standard deviation of particle size σ divided by the average particle size.

[0251] Where σ is the standard deviation of particle size, x i For each particle, the first particle size is calculated. Let n be the first-order average particle size of the statistical particles, and n be the total number of statistical particles. The first-order average particle size of the statistical particles is the total first-order particle size of the statistical particles divided by the total number of statistical particles.

[0252] In some embodiments, the second lithium-containing transition metal phosphate material satisfies at least one of (a1)-(d1):

[0253] (a1) The (Dv90-Dv10) / Dv50 ratio of the second lithium-containing transition metal phosphate material is 1-3;

[0254] (b1) The Dv50 of the second lithium-containing transition metal phosphate material is 0.35 μm-1.5 μm;

[0255] (c1) The Dv10 of the second lithium-containing transition metal phosphate material is 0.1 μm-0.4 μm;

[0256] (d1) The Dv90 of the second lithium-containing transition metal phosphate material is 2.5 μm-6 μm.

[0257] The volumetric distribution particle sizes Dv10, Dv50, and Dv90 of a material are known in the art, representing the particle sizes corresponding to a cumulative volumetric distribution percentage of 10%, 50%, and 90%, respectively. These sizes can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016, Particle Size Distribution by Laser Diffraction. The testing instrument can be the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0258] In some embodiments, based on the total weight of the positive electrode active material, the weight percentage of the first lithium transition metal phosphate material is greater than 0% and less than or equal to 20%, optionally 3%-15%; and / or, the weight percentage of the second lithium transition metal phosphate material is greater than or equal to 80% and less than 100%, optionally 85%-97%.

[0259] In some embodiments, the preparation method of the positive electrode active material is as follows:

[0260] 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.

[0261] The third lithium-containing transition metal phosphate material comprises a third core and a third carbon coating layer covering the outer surface of the third core.

[0262] The primary average particle size of the third lithium-containing transition metal phosphate material is greater than that of the second lithium-containing transition metal phosphate material.

[0263] The molar percentage of Mn in the third lithium-containing transition metal phosphate material is less than that in the second lithium-containing transition metal phosphate material.

[0264] The primary average particle size of the third lithium-containing transition metal phosphate material is 250 nm to 4000 nm.

[0265] In some embodiments, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.5, more preferably 0-0.1, and even more preferably 0.

[0266] In some embodiments, the molar ratio of Mn in the third lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.5, more preferably 0-0.1, and even more preferably 0.02.

[0267] In some embodiments, the molar percentage of Mn in the third lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.5, and more preferably 0.2.

[0268] 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 is 1%-15%, and / or the weight percentage of the second lithium transition metal phosphate material is 30%-90%, and / or the weight percentage of the third lithium transition metal phosphate material is 5%-55%.

[0269] In some embodiments, the third lithium-containing transition metal phosphate material satisfies the following relationship: 1.5 ≤ A / B ≤ 10.

[0270] Where A is the specific surface area of ​​the third lithium-containing transition metal phosphate material; B% is the mass content of the third carbon coating layer in the third lithium-containing transition metal phosphate material.

[0271] The mass content of the carbon coating layer of a material can be determined by methods and equipment known in the art, for example as follows: the carbon content is tested by infrared absorption method after the material is burned in a high-frequency induction furnace, and the specific testing procedure is in accordance with the standard GB / T 20123-2006 / ISO 15350:2000.

[0272] The specific surface area of ​​a material can be determined using methods and equipment known in the art, as exemplified below: The specific surface area is tested using the gas adsorption method, according to the GB / T19587-2017 testing standard. Specifically, the material is taken as a sample, and the sample tube is immersed in liquid nitrogen at -196℃. The amount of nitrogen adsorbed on the solid surface at different pressures (0.05-0.30) is measured. Based on the BET multilayer adsorption theory and its formula, the amount of monolayer adsorption of the sample is calculated, thereby determining the specific surface area of ​​the material.

[0273] In some embodiments, the specific surface area of ​​the third lithium-containing transition metal phosphate material is 3 m². 2 / g-12m 2 / g.

[0274] In some embodiments, the mass content of the third carbon coating layer is 0.8%-2.0% based on the mass of the third lithium-containing transition metal phosphate material.

[0275] In some embodiments, the third lithium-containing transition metal phosphate material satisfies at least one of (a2)-(f2):

[0276] (a2) The Dv10 of the third lithium-containing transition metal phosphate material is 0.2 μm-2 μm;

[0277] (b2) The Dv50 of the third lithium-containing transition metal phosphate material is 0.5 μm-5 μm;

[0278] (c2) The Dv90 of the third lithium-containing transition metal phosphate material is 1.5 μm-10 μm;

[0279] (d2) The Dv99 of the third lithium-containing transition metal phosphate material is 2μm-12μm;

[0280] (e2) The compacted density of the third lithium-containing transition metal phosphate material at a pressure of 29400 N is 2.25 g / cm³. 3 -2.60g / cm 3 ;

[0281] (f2) The powder resistivity of the third lithium-containing transition metal phosphate material is 0 Ω·cm to 59 Ω·cm.

[0282] In this paper, the term "Dv10" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 10%.

[0283] In this paper, the term "Dv50" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 10%.

[0284] In this paper, the term "Dv90" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 90%.

[0285] In this paper, the term "Dv99" refers to the particle size at which the cumulative volumetric particle size distribution percentage in a material reaches 99%.

[0286] The Dv10, Dv50, Dv90, and Dv99 of the material can be measured using methods and equipment known in the art. For example, they can be determined using a laser particle size analyzer (Malvern Master Size 3000) with reference to GB / T19077.1-2016.

[0287] The compacted powder density of a material can be measured using a compaction density instrument, referring to GB / T 24533-2009. Specifically, a certain amount of material powder is placed on a special compaction mold (the mold diameter is known). The mold is hollow in the middle and has a metal disc at the top and bottom. The powder is placed between the metal discs, and a metal cylinder is placed on top. The mold is placed on the compaction density instrument, and the pressure is set to 29400N. The thickness of the powder under 29400N pressure can be read on the instrument. The compacted powder density is then ρ = m / v, where v = (S × H), m is the mass of the powder, S is the bottom area of ​​the mold, and H is the thickness of the compacted powder. The compaction density instrument model is UTM7305; the manufacturer is Sansi Zongheng.

[0288] The powder resistivity of a material can be measured using methods and equipment known in the art. For example, it can be measured using a powder resistivity meter (Suzhou Jingge, ST2722 type) according to GB / T 33822-2017. Specifically, a certain amount of material (e.g., 1g) is weighed and added to the feeding chamber of the powder resistivity meter, a pressure of 8MPa is applied, and the forward and reverse resistivity of the material are measured separately. The average value of the two is taken as the powder resistivity of the material.

[0289] 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 ,

[0290] 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,

[0291] 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,

[0292] 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 ,

[0293] 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

[0294] 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.

[0295] [Positive electrode plate]

[0296] 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.

[0297] 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.

[0298] In some embodiments, the positive electrode film layer further includes a binder and a conductive agent.

[0299] 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).

[0300] In some embodiments, the areal density of the positive electrode film is 300 mg / 1540 mm². 2 -580mg / 1540mm 2 .

[0301] The areal density of the positive electrode film can be tested using methods known in the art. An example is as follows: Place the battery in a 25°C oven and let it stand for 2 hours. Once the battery temperature remains at 25°C, discharge the battery at a constant current of 1 / 3C to 2.0V. Disassemble the battery to obtain the positive electrode sheet. Treat the residual electrolyte with dimethyl carbonate solvent, dry the electrode sheet, and cut it 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.

[0302] In some embodiments, the areal density of the positive electrode film is 300 mg / 1540 mm². 2340mg / 1540mm 2 380mg / 1540mm 2 420mg / 1540mm 2 460mg / 1540mm 2 500mg / 1540mm 2 540mg / 1540mm 2 580mg / 1540mm 2 , or the range between any two of the above values.

[0303] In some embodiments, the compaction density of the positive electrode film is 2.25 g / cm³. 3 -2.75g / cm 3 .

[0304] The compaction density of the positive electrode film can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven environment and left to stand for 2 hours. Once the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.0V. The battery is then disassembled to obtain the positive electrode sheet. The residual electrolyte is treated with dimethyl carbonate solvent, the electrode sheet is dried, and it is cut into small circular pieces with an area of ​​S. The weight is recorded as W1, and the thickness T1 of the positive electrode sheet is measured using a micrometer. Then, the positive electrode film layer of the weighed electrode sheet is wiped off, and the weight of the current collector is recorded as W2. The thickness T2 of the current collector is measured using a micrometer. The compaction density of the positive electrode film layer is then PD = (W1-W2) / [(T1-T2)×S].

[0305] 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.

[0306] When the compaction density of the positive electrode sheet is within a suitable range, the battery has a superior volumetric energy density.

[0307] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0308] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0309] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0310] 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.

[0311] [Negative electrode plate]

[0312] 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.

[0313] 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.

[0314] 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.).

[0315] 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.

[0316] 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).

[0317] 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.

[0318] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0319] 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.

[0320] [Electrolytes]

[0321] 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.

[0322] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0323] 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.

[0324] 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.

[0325] [Isolation membrane]

[0326] The separator used in this application is the separator described above. Furthermore, the separator used in this application can be used in combination with other separators commonly used in the art, as needed.

[0327] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0328] 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.

[0329] 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.

[0330] [Rechargeable Battery]

[0331] In one embodiment of this application, a secondary battery is provided, including a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the binder in the active material layer of the positive electrode includes polymers according to any embodiment of this application.

[0332] 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.

[0333] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0334] 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.

[0335] 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.

[0336] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square-structured secondary battery 5 as an example.

[0337] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0338] 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.

[0339] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0340] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0341] 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.

[0342] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0343] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0344] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0345] Figure 8 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0346] 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.

[0347] Example

[0348] 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.

[0349] Table 1. Relevant parameters and sources of the first lithium-containing transition metal phosphate material.

[0350] Table 2. Relevant parameters and sources of the second lithium-containing transition metal phosphate material.

[0351] Table 3. Relevant parameters and sources of the third lithium-containing transition metal phosphate material.

[0352] I. Preparation Method

[0353] Example 1

[0354] (1) The first lithium-containing transition metal phosphate material A1 and the second lithium-containing transition metal phosphate material B1 are mixed in a mass ratio of 15%:85% to obtain a positive electrode active material. The above-mentioned mixed positive electrode active material, conductive agent conductive carbon black, and binder polyvinylidene fluoride are mixed 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.

[0355] Adjust the viscosity of the thoroughly mixed slurry to 8000-20000 mPa·s until it no longer separates. Then, use a double-sided, double-control coating machine to apply the slurry at a rate of 420 mg / 1540 mm. 2 The coating is applied to the surface of the substrate aluminum foil, and then dried, cold-pressed, slit, and sheeted to finally obtain the positive electrode sheet.

[0356] (2) Preparation of negative electrode sheet:

[0357] Artificial graphite, conductive carbon black, 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 coated on a copper foil substrate at a concentration of 211 mg / 1540 mm2. After drying, cold pressing, slitting, and sheet forming, a negative electrode sheet was obtained.

[0358] (3) Diaphragm

[0359] Polypropylene film is used as the separator.

[0360] (4) Electrolyte

[0361] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) were mixed evenly in a volume ratio of 1:1:1:1. LiPF6 was then added and dissolved in the organic solvent and stirred evenly to achieve an electrolyte concentration of 1 mol / L, thus obtaining the electrolyte of Example 1.

[0362] (5) Battery fabrication:

[0363] 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.

[0364] Examples 2-15 and Comparative Examples 1-2 are prepared in a similar manner to Example 1, except that the types or mass contents of the first lithium-containing transition metal phosphate, the second lithium-containing transition metal phosphate, and / or the third lithium-containing transition metal phosphate in the positive electrode active material are adjusted, as follows:

[0365] Table 4

[0366] II. Testing Methods

[0367] 1. Battery fast charging performance test

[0368] At 40℃, the battery was charged at a constant current of 4C to the charging cutoff voltage of 4.1V, then charged at a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to the discharge cutoff voltage of 2.0V. Its actual capacity was recorded as C0.

[0369] Then, the battery is sequentially charged at a constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0 until the full battery charging cutoff voltage of 4.1V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, it is discharged at 1C0 until the full battery discharge cutoff voltage of 2.0V. The state of charge (SOC) is recorded at different charging rates until it reaches 10%, 20%, 30%...80%. By plotting the negative electrode potential corresponding to the state of charge (SOC), rate-negative electrode potential curves are generated for different SOC states. Linear fitting yields the charging rate corresponding to a negative electrode potential of 0V at each SOC state. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T from 10% SOC to 80% SOC is calculated using the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%. A shorter charging time T indicates better fast-charging performance of the secondary battery.

[0370] 2. Battery storage performance

[0371] Place the battery in a 40℃ oven and let it stand for 2 hours until the battery temperature reaches 40℃. Then, discharge the battery at a constant current of 1 / 3C to 2.0V. After standing for 5 minutes, charge the battery at a constant current of 1 / 3C to 4.1V, and then charge it at a constant voltage of 4.1V to a current of 0.05C. After standing for 5 minutes, discharge the battery at a constant current of 1 / 3C to 2.0V. This is 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 take out the battery and test the remaining capacity at 40℃ until the discharge capacity of the secondary battery decays to 80%. Record the storage time at this point.

[0372] 3. Volumetric energy density of the battery

[0373] Battery cell capacity test: The battery cell was left to stand at 40℃ for 2 hours to ensure the temperature of the battery cell was 40℃. Then the battery was discharged at a constant current of 1 / 3C to 2.0V. After standing for 5 minutes, the battery cell was charged at a constant current of 1 / 3C to 4.1V. The constant voltage charging at 4.1V continued until the current was 0.05C. After standing for 5 minutes, the battery cell was discharged at a constant current of 1 / 3 to 2.0V. The total discharge capacity C0 and the total discharge energy E0 of the battery cell were recorded. The unit of total discharge energy is Wh.

[0374] 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).

[0375] 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.

[0376] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0377] Secondary batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in the table below.

[0378] Table 5

[0379] The positive electrode film layer in Embodiments 1-15 of this application includes a first type of particles and a second type of particles, wherein the primary particle size of the first type of particles is 50nm-180nm, the primary particle size of the second type of particles is greater than 180nm and less than 900nm, and the average value of the Mn molar ratio of the first type of particles is less than the average value of the Mn molar ratio of the second type of particles.

[0380] As can be seen from the comparison between Examples 1-15 and Comparative Examples 1-2, this application controls the average value of the Mn molar ratio of the first type of particles to be less than the average value of the Mn molar ratio of the second type of particles. The positive electrode active material has both high powder compaction density and specific capacity, which can extend the battery storage time, improve the battery storage performance, and increase the battery energy density.

[0381] Table 6

[0382] As can be seen from the comparison between Example 4 and Example 3, based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0%-8%, which can extend the storage life of the battery and improve the storage performance of the battery.

[0383] A comparison of Examples 1-2 and Example 3 shows that the average molar ratio of Mn in the first type of particles is 0-0.2, which can improve the storage time of the battery and extend its storage life.

[0384] As can be seen from the comparison between Example 2 and Examples 1 and 3, the average molar ratio of Mn in the first type of particles is 0.1-0.2, which can further improve the energy density of the battery.

[0385] As can be seen from Examples 2 and 5-8, the average molar ratio of Mn in the second type of particles is 0.4-0.9, and the battery has high energy density and long storage life.

[0386] As can be seen from Examples 1 and 10, the area ratio of the first type of particles is greater than 0% and less than or equal to 30%, and the area ratio of the second type of particles is greater than or equal to 70% and less than 100%, and the battery has a long storage life and high energy density.

[0387] Table 7

[0388] As can be seen from the comparison between Example 12 and Example 10, the positive electrode film layer contains third-type particles with a primary particle size greater than 900 nm and less than or equal to 5 μm. Based on the total area of ​​the primary particles in the positive electrode film layer, the powder compaction density of the material can be improved, which can further extend the storage time of the battery, improve the storage performance of the battery, and at the same time ensure that the battery has a high energy density.

[0389] As can be seen from the comparison between Examples 12-13 and Example 11, controlling the average value of the Mn molar ratio of the third type of particles to be less than the average value of the Mn molar ratio of the second type of particles increases the specific capacity of the material, which can further extend the battery storage time, shorten the battery charging time, extend the battery storage time, and improve the battery storage performance and rate performance.

[0390] As can be seen from Examples 13 and 12, controlling the average Mn molar ratio of the third type of particles to be 0.1-0.3 can further extend the battery storage time, shorten the battery charging time, improve the battery storage performance and rate performance, and also increase the battery energy density.

[0391] As can be seen from Examples 11-15, the positive electrode film contains a first type of particles, a second type of particles, and a third type of particles. The area ratio of the first type of particles is 5%-15%, the area ratio of the second type of particles is 45%-85%, and the area ratio of the third type of particles is 10%-40%. The battery has a long storage life, a short charging time, and a high energy density, taking into account the battery's storage performance, rate performance, and energy density.

[0392] 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: Includes positive electrode, negative electrode, and electrolyte. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer comprises a first type of particles and a second type of particles, wherein the first type of particles and the second type of particles comprise lithium-containing transition metal phosphate materials. The first type of particles has a primary particle size of 50nm-180nm; the second type of particles has a primary particle size greater than 180nm and less than 900nm. The average molar percentage of Mn in the first type of particles is less than the average molar percentage of Mn in the second type of particles. 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.

2. The secondary battery according to claim 1, characterized by Based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0%-12%, optionally 0%-8%, more preferably 0%-6%, and even more preferably 0%.

3. The secondary battery according to claim 1, characterized by Based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0.02%-12%, optionally 0.02%-8%, more preferably 0.02%-6%, and even more preferably 0.02%.

4. The secondary battery according to claim 1, characterized by Based on the total number of moles of Mn in the primary particles of the positive electrode film, the molar percentage of Mn in the first type of particles is 0.2%-12%, optionally 0.2%-8%, more preferably 0.2%-6%, and even more preferably 0.2%.

5. The secondary battery according to any one of claims 1 to 4, characterized by, The ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0-0.8, optionally 0-0.4, and more preferably 0.

6. The secondary battery according to any one of claims 1 to 4, characterized by The ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0.0003-0.8, optionally 0.0003-0.4, and more preferably 0.0003.

7. The secondary battery according to any one of claims 1 to 4, characterized by The ratio of the average molar percentage of Mn in the first type of particles to the average molar percentage of Mn in the second type of particles is 0.002-0.8, preferably 0.002-0.4, and more preferably 0.

002.

8. The secondary battery according to any one of claims 1 to 7, characterized by, The average molar ratio of Mn in the second type of particles is 0.4-0.9, and can be selected as 0.5-0.

9.

9. The secondary battery according to any one of claims 1 to 8, characterized by, The average molar ratio of Mn in the first type of particles is 0-0.6, optionally 0-0.4, more preferably 0-0.2, and even more preferably 0.

10. The secondary battery according to any one of claims 1 to 8, characterized by The average molar ratio of Mn in the first type of particles is 0.02-0.6, preferably 0.02-0.4, more preferably 0.02-0.2, and even more preferably 0.

02.

11. The secondary battery according to any one of claims 1 to 8, characterized by The average molar ratio of Mn in the first type of particles is 0.1-0.2, and can be selected as 0.

1.

12. The secondary battery according to any one of claims 1 to 11, characterized by Based on the total area of ​​the primary particles in the positive electrode film, the area percentage of the first type of particles is greater than 0% and less than or equal to 30%, which can be selected as 5%-20%; and / or, the area percentage of the second type of particles is greater than or equal to 70% and less than 100%, which can be selected as 80%-95%.

13. The secondary battery according to any one of claims 1 to 11, characterized by The positive electrode film layer comprises third type particles, the third type particles comprise the lithium-containing transition metal phosphate material, the primary particle size of the third type particles is greater than 900 nm and less than or equal to 5 μm, The area percentage of the third type particles is greater than or equal to 5% based on the total area of the primary particles of the positive electrode film layer.

14. The secondary battery according to claim 13, characterized by The average value of the Mn mole percentage of the third type particles is less than the average value of the Mn mole percentage of the second type particles.

15. The secondary battery according to claim 13 or 14, characterized by The mole percentage of Mn in the third type particles is 0%-50%, optionally 0%-30%, more optionally 0%-10%, further optionally 0%, based on the total moles of Mn in the primary particles of the positive electrode film layer.

16. The secondary battery according to claim 13 or 14, characterized by The mole percentage of Mn in the third type particles is 5%-50%, optionally 5%-30%, more optionally 5%-10%, further optionally 5%, based on the total moles of Mn in the primary particles of the positive electrode film layer.

17. The secondary battery according to claim 13 or 14, characterized by The mole percentage of Mn in the third type particles is 10%-50%, optionally 10%-30%, more optionally 10%, based on the total moles of Mn in the primary particles of the positive electrode film layer.

18. The secondary battery according to any one of claims 13 to 17, characterized by, The ratio of the average value of the Mn mole percentage of the third type particles to the average value of the M mole percentage of the second type particles is 0-0.8, optionally 0-0.5, more optionally 0.

19. The secondary battery according to any one of claims 13 to 17, characterized by The ratio of the average value of the Mn mole percentage of the third type particles to the average value of the Mn mole percentage of the second type particles is 0.0003-0.8, optionally 0.0003-0.5, more optionally 0.0003.

20. The secondary battery according to any one of claims 13 to 17, characterized by The ratio of the average value of the Mn mole percentage of the third type particles to the average value of the Mn mole percentage of the second type particles is 0.002-0.8, optionally 0.002-0.5, more optionally 0.

002.

21. The secondary battery according to any one of claims 13 to 20, characterized by The average value of the Mn mole percentage of the third type particles is 0-0.6, optionally 0-0.5, more optionally 0-0.1, further optionally 0.

22. The secondary battery according to any one of claims 13 to 20, characterized by The average value of the Mn mole percentage of the third type particles is 0.02-0.6, optionally 0.02-0.2, more optionally 0.

02.

23. The secondary battery according to any one of claims 13 to 20, characterized by The average value of the Mn mole percentage of the third type particles is 0.1-0.3, optionally 0.

1.

24. The secondary battery according to any one of claims 13 to 23, characterized by, The area percentage of the first type particles is 5%-15%, and / or the area percentage of the second type particles is 45%-85%, and / or the area percentage of the third type particles is 10%-40%, based on the total area of the primary particles of the positive electrode film layer.

25. The secondary battery according to any one of claims 1 to 24, characterized by The average value of the Mn mole percentage of the primary particles of the positive electrode film layer is 0.2-0.9, optionally 0.4-0.

8.

26. The secondary battery according to any one of claims 1 to 25, characterized by The primary particle size distribution index of the second type particles is greater than 0 and less than or equal to 0.5, The particle size distribution index refers to the ratio of the standard deviation of the primary particle size of the second type particles to the average primary particle size of the second type particles.

27. The secondary battery according to any one of claims 13 to 26, characterized by The composition general formula of the lithium-containing transition metal phosphate material of the second type of particles includes Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 , 0.8≤m1≤1.2, x1≥0, y1>0, 0.9≤x1+y1≤1, 0.95≤z1≤1.1, 3.5≤n1≤4, 0≤a1≤0.1, 0≤b1≤0.1, 0≤c1≤0.1, 0≤d1≤0.1, and / or, The composition general formula of the lithium-containing transition metal phosphate material of the first type of particles includes Li m2 A2 a2 Fe x2 Mn y2 M2 b2 P z2 Q2 c2 O n2 N2 d2 , 0.8≤m2≤1.2, x2≥0, y2≥0, 0.9≤x2+y2≤1, 0.95≤z2≤1.1, 3.5≤n2≤4, 0≤a2≤0.1, 0≤b2≤0.1, 0≤c2≤0.1, 0≤d2≤0.1, and / or, The composition general formula of the lithium-containing transition metal phosphate material of the third type of particles includes Li m3 A3 a3 Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3 , 0.8≤m3≤1.2, x3≥0, y3≥0, 0.9≤x3+y3≤1, 0.95≤z3≤1.1, 3.5≤n3≤4, 0≤a3≤0.1, 0≤b3≤0.1, 0≤c3≤0.1, 0≤d3≤0.1, wherein A1, A2, A3 each independently comprises one or more of Al, Na, K, Mg, M1, M2, M3 each independently comprises one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1, Q2, Q3 each independently comprises one or more of B, S, Si, N, N1, N2, N3 each independently comprises one or more of S, F, Cl, Br.

28. The secondary battery according to any one of claims 1 to 27, characterized by The positive electrode film layer includes a positive electrode active material, the positive electrode active material includes the lithium-containing transition metal phosphate material, and the powder compaction density of the positive electrode active material under a pressure of 29400 N is 2.35 g / cm 3 -2.60 g / cm 3 .

29. The secondary battery according to claim 28, characterized by The positive electrode active material has a gram capacity of 135 mAh / g-150 mAh / g at 40℃ and a discharge rate of 1 / 3C.

30. The secondary battery according to claim 28 or 29, characterized by The positive electrode film layer further comprises a binder and a conductive agent, and the mass ratio of the positive electrode active material, the binder and the conductive agent in the positive electrode film layer is (92-99):(0.5-3):(0.5-3).

31. The secondary battery according to any one of claims 1 to 30, characterized by The single-sided areal density of the positive electrode film layer is 300 mg / 1540 mm 2 - 580 mg / 1540 mm 2 .

32. The secondary battery according to any one of claims 1 to 31, characterized by The compacted density of the positive electrode film layer is 2.25 g / cm 3 - 2.75 g / cm 3 .

33. An electrical device, comprising: The power utilization device comprises the secondary battery of any one of claims 1-32.

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