Secondary battery and electric device

Abstract

A secondary battery and an electrical device. The secondary battery (5) includes a positive electrode (10), a negative electrode, and an electrolyte. 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 (110). The positive electrode film (120) includes first-type particles (1210) and second-type particles (1220). The first-type particles (1210) and the second-type particles (1220) include lithium-containing transition metal phosphate materials. The primary particle size of the first-type particles (1210) is greater than 180 nm and less than 900 nm. The primary particle size of the second-type particles (1220) is greater than or equal to 900 nm and less than or equal to 5 μm. The average value of the Mn molar ratio of the second-type particles (1220) is less than the average value of the Mn molar ratio of the first-type particles (1210). The Mn molar ratio refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

Description

Secondary battery and power consuming device TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and a power consuming device. BACKGROUND

[0002] Secondary batteries have the advantages of high energy density, high working voltage, low self-discharge rate, small size, and light weight, and have a wide range of applications.

[0003] At present, with the rapid development of electric vehicles and mobile electronic devices, people have increasingly high requirements for the energy density and rate performance of secondary batteries. How to improve the energy density of the battery while also taking into account the rate performance of the battery is a technical problem that needs to be solved in the current application field of secondary batteries.

[0004] SUMMARY

[0005] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery and a power consuming device, the secondary battery having high energy density and excellent rate performance.

[0006] A first aspect of the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte,

[0007] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector,

[0008] The positive electrode film layer comprises first particles and second particles, and the first particles and the second particles comprise lithium-containing transition metal phosphate materials,

[0009] The primary particle size of the first particles is greater than 180 nm and less than 900 nm, and the primary particle size of the second particles is greater than or equal to 900 nm and less than or equal to 5 μm,

[0010] The average value of the Mn molar ratio of the second particles is less than the average value of the Mn molar ratio of the first particles,

[0011] The Mn molar ratio refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0012] The positive electrode active material includes two types of particles with different primary particle sizes, which can realize the purpose of mutual filling of the particles of different sizes to fill the gaps, so that the particles in the positive electrode active material are more densely packed, the compaction density of the electrode sheet is improved, and the energy density of the battery is improved. However, the second type of particles has a relatively large primary particle size, which makes the migration path of lithium ions in the particles longer, resulting in an increase in the discharge polarization of the second type of particles and a decrease in the specific capacity, affecting the specific capacity and kinetic performance of the material, and further affecting the energy density and rate performance of the battery. The Mn molar ratio of the particles affects the conductivity of the particles. By controlling the average value of the Mn molar ratio of the second type of particles with a relatively large primary particle size to be less than the average value of the Mn molar ratio of the first type of particles with a relatively small primary particle size, the conductivity of the second type of particles with a relatively large primary particle size can be improved, the discharge polarization of the second type of particles can be alleviated, and the specific capacity and kinetic performance of the material can be improved. While improving the powder compaction density of the material and the energy density of the battery, the conductivity of the material can also be improved, and the rate performance of the battery can be improved.

[0013] In any embodiment, the mole percentage of Mn in the second type of particles is 0%-50%, optionally 0%-30%, more optionally 0%-10%, and further optionally 0%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer.

[0014] Controlling the mole percentage of Mn in the second type of particles within a suitable range can further improve the conductivity of the second type of particles, alleviate the discharge polarization of the second type of particles, further improve the rate performance of the battery, and also facilitate the concentration of sufficient manganese elements in the first type of particles with a small primary particle size, so that the first type of particles contribute more platform capacity and improve the energy density of the battery, which is suitable for high-rate and high-energy-density batteries.

[0015] In any embodiment, the mole percentage of Mn in the second type of particles is 5%-50%, optionally 5%-30%, more optionally 5%-10%, and further optionally 5%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer.

[0016] Controlling the mole percentage of Mn in the second type of particles within a suitable range can improve the conductivity and kinetic performance of the material, and also facilitate the contribution of a certain platform capacity by Mn in the second type of particles, and can alleviate the influence of the Mn dissolution phenomenon caused by the excessive concentration of Mn in the first type of particles with a relatively small primary particle size on the cycle performance and storage performance of the battery, so that the battery is more suitable for application scenarios with certain requirements for storage performance and / or cycle performance.

[0017] In any embodiment, the mole percentage of Mn in the second type of 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.

[0018] Controlling the mole percentage of Mn in the second type of particles within a suitable range can further alleviate the influence of Mn dissolution phenomenon on the cycle performance and storage performance of the battery while the second type of particles have good electrical conductivity, making the battery more suitable for application scenarios with high demands for storage performance and / or cycle performance.

[0019] In any embodiment, the ratio of the average value of the mole percentage of Mn in the second type of particles to the average value of the mole percentage of Mn in the first type of particles is 0-0.8, optionally 0-0.5, more optionally 0.

[0020] Controlling the ratio of the average value of the mole percentage of Mn in the second type of particles to the average value of the mole percentage of Mn in the first type of particles within a suitable range can improve the electrical conductivity of the second type of particles while also taking into account the high plateau capacity contributed by the first type of particles, thereby comprehensively improving the energy density and rate performance of the battery.

[0021] In any embodiment, the ratio of the average value of the mole percentage of Mn in the second type of particles to the average value of the mole percentage of Mn in the first type of particles is 0.0003-0.8, optionally 0.0003-0.5, more optionally 0.0003.

[0022] In any embodiment, the ratio of the average value of the mole percentage of Mn in the second type of particles to the average value of the mole percentage of Mn in the first type of particles is 0.002-0.8, optionally 0.002-0.5, more optionally 0.002.

[0023] Controlling the ratio of the average value of the mole percentage of Mn in the second type of particles to the average value of the mole percentage of Mn in the first type of particles within a suitable range allows the battery to have excellent rate performance, storage performance, and energy density.

[0024] In any embodiment, the average value of the mole percentage of Mn in the first type of particles is 0.4-0.9, optionally 0.5-0.9.

[0025] Controlling the average value of the mole percentage of Mn in the first type of particles within a suitable range allows the first type of particles to have high plateau capacity while also ensuring that the first type of particles have a certain electrical conductivity, which is conducive to the first type of particles contributing sufficient capacity and thereby improving the energy density of the battery.

[0026] In any embodiment, the average value of the mole fraction of Mn of the second type of particles is 0-0.6, optionally 0-0.5, more optionally 0-0.1, and further optionally 0.

[0027] Controlling the average value of the mole fraction of Mn of the second type of particles in a suitable range can improve the electrical conductivity of the second type of particles, improve the electrical conductivity of the overall material, and improve the rate performance of the battery.

[0028] In any embodiment, the average value of the mole fraction of Mn of the second type of particles is 0.02-0.6, optionally 0.02-0.2, and more optionally 0.02.

[0029] In any embodiment, the average value of the mole fraction of Mn of the second type of particles is 0.1-0.3, and optionally 0.1.

[0030] Controlling the average value of the mole fraction of Mn of the second type of particles in a suitable range can improve the electrical conductivity of the second type of particles and the material, and also enable the second type of particles to have a certain platform capacity, further improving the energy density of the battery.

[0031] In any embodiment, the area fraction of the first type of particles is 20%-95%, optionally 20%-80%, and more optionally 40%-60%, and / or the area fraction of the second type of particles is 5%-80%, optionally 15%-80%, and more optionally 25%-60%, based on the total area of primary particles of the positive electrode film layer.

[0032] Controlling the area fraction of the first type of particles and the second type of particles in a suitable range can achieve the gradation of large and small particles, improve the compaction density of the material, and also enable the first type of particles with a relatively high Mn content to provide a platform capacity, and enable the second type of particles with a suitable content and high compaction density to improve the powder compaction density of the material, and also reduce the influence of the second type of particles with a large particle size on the electrical conductivity of the material, which is conducive to obtaining a battery with high energy density and excellent rate performance.

[0033] In any embodiment, the positive electrode film layer comprises a third type of particles, the third type of particles comprising the lithium-containing transition metal phosphate material, and the primary particle size of the third type of particles is 50 nm-180 nm,

[0034] In any embodiment, the area fraction of the third type of particles is greater than or equal to 5% and less than or equal to 30%, based on the total area of primary particles of the positive electrode film layer.

[0035] The third type of particles with a smaller primary particle size and a suitable area ratio can be filled into the pores between the first type of particles and the second type of particles, making the filling between the materials more compact, further improving the powder compaction density of the material, improving the compaction density of the pole piece, and being conducive to obtaining a high-energy-density battery.

[0036] In any embodiment, the average value of the Mn molar ratio of the third type of particles is less than the average value of the Mn molar ratio of the first type of particles.

[0037] As described above, the third type of particles with an ultra-small particle size can further improve the powder compaction density of the material. However, the third type of particles with an ultra-small particle size have a large specific surface area, and the surface activity increases significantly, making it easier to contact the electrolyte and cause side reactions and exacerbate manganese dissolution, thereby affecting the cycle performance and storage performance of the battery.

[0038] By 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 first type of particles, the degree of side reactions and manganese dissolution of the third type of particles with the electrolyte can be reduced, thereby improving the cycle performance and storage performance of the battery while improving the energy density of the battery.

[0039] In any embodiment, the mole percentage of Mn in the third type of particles is 0%-12%, optionally 0%-8%, more optionally 0%-6%, and further optionally 0%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer.

[0040] Controlling the mole percentage of Mn in the third type of particles within a suitable range reduces the likelihood of side reactions and manganese dissolution of the third type of particles with the electrolyte, improves the cycle performance and storage performance of the battery, prolongs the service life of the battery, and the battery is suitable for use in use scenarios with higher requirements for cycle performance and / or storage performance.

[0041] In any embodiment, the mole percentage of Mn in the third type of particles is 0.02%-12%, optionally 0.02%-8%, more optionally 0.02%-6%, and further optionally 0.02%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer.

[0042] In any embodiment, the mole percentage of Mn in the third type of particles is 0.2%-12%, optionally 0.2%-8%, more optionally 0.2%-6%, and further optionally 0.2%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer.

[0043] The molar percentage of Mn in the third type of particles is controlled within a suitable range, which reduces the possibility of the third type of particles dissolving manganese while enabling the third type of particles with excellent electrical conductivity to fully exert the specific capacity and platform capacity, thereby improving the energy density of the battery and being more suitable for use scenarios with high energy density requirements.

[0044] In any embodiment, the ratio of the average value of the molar percentage of Mn in the third type of particles to the average value of the molar percentage of Mn in the first type of particles is 0-0.8, optionally 0-0.4, and more optionally 0.

[0045] The ratio of the average value of the molar percentage of Mn in the third type of particles to the average value of the molar percentage of Mn in the first type of particles is controlled within a suitable range, which improves the cycle and storage stability of the third type of particles while enabling the first type of particles to have high platform capacity, thereby comprehensively improving the energy density and storage performance and cycle performance of the battery.

[0046] In any embodiment, the ratio of the average value of the molar percentage of Mn in the third type of particles to the average value of the molar percentage of Mn in the first type of particles is 0.0003-0.8, optionally 0.0003-0.4, and more optionally 0.0003.

[0047] In any embodiment, the ratio of the average value of the molar percentage of Mn in the third type of particles to the average value of the molar percentage of Mn in the first type of particles is 0.002-0.8, optionally 0.002-0.4, and more optionally 0.002.

[0048] The ratio of the average value of the molar percentage of Mn in the third type of particles to the average value of the molar percentage of Mn in the first type of particles is controlled within a suitable range, which is conducive to further improving the energy density of the battery and being more suitable for use scenarios with high energy density requirements.

[0049] In any embodiment, the average value of the molar percentage of Mn in the third type of particles is 0-0.6, optionally 0-0.4, more optionally 0-0.2, and further optionally 0.

[0050] The average value of the molar percentage of Mn in the third type of particles is controlled within a suitable range, which reduces the possibility of the third type of particles reacting with the electrolyte and dissolving manganese, improves the stability of the third type of particles, and improves the cycle performance and storage performance of the battery.

[0051] In any embodiment, the average value of the molar percentage of Mn in the third type of particles is 0.02-0.6, optionally 0.02-0.4, more optionally 0.02-0.2, and further optionally 0.02.

[0052] In any embodiment, the average value of the Mn molar ratio of the third type of particles is 0.1-0.2, which can be 0.1.

[0053] Controlling the average value of the Mn molar ratio of the third type of particles within a suitable range can improve the stability of the third type of particles, while also enabling the third type of particles to have a high gravimetric capacity, so that the battery has good storage performance and high energy density.

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

[0055] Controlling the area ratios of particles of different particle sizes within a suitable range can achieve the purpose of the contribution of the flat-pressed capacity and gravimetric capacity of the first type of particles with high manganese content to the energy density, while also reducing the impact of the second type of particles with large particle sizes on the rate performance of the battery and reducing the impact of the third type of particles with small particle sizes on the cycle performance and storage performance of the battery, so that the battery has high energy density, good cycle performance, good storage performance, and rate performance.

[0056] In any embodiment, the average value of the Mn molar ratio of the primary particles of the positive electrode film layer is 0.2-0.9, which can be 0.4-0.8.

[0057] Controlling the average value of the Mn molar ratio of the overall particles within a suitable range can enable the material to have a high platform capacity while also having excellent cycle stability, storage stability, and electrical conductivity, which is conducive to obtaining a battery with high energy density, excellent cycle performance, and rate performance.

[0058] In any embodiment, the particle size distribution index of the primary particle size of the first 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 first type of particles to the average primary particle size of the first type of particles.

[0060] By controlling the particle size distribution index of the primary particle size of the first type of particles within a suitable range, the discharge behavior of each particle in the first type of particles during the cycle process of the battery can be improved to be consistent, and the possibility of overcharging and overdischarging of each particle during the charging and discharging process can be reduced, which is conducive to improving the structural stability of the material and further improving the cycle performance of the battery.

[0061] In any embodiment, the composition general formula of the lithium-containing transition metal phosphate material of the first type of particles includes Li m1 A1 a1 Fex1 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,

[0063] The composition general formula of the lithium-containing transition metal phosphate material of the second 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,

[0064] 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 ,

[0065] 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,

[0066] wherein A1, A2, A3 each independently includes one or more of Al, Na, K, Mg, M1, M2, M3 each independently includes one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q1, Q2, Q3 each independently includes one or more of B, S, Si, N, N1, N2, N3 each independently includes one or more of S, F, Cl, Br.

[0067] In any embodiment, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises the lithium-containing transition metal phosphate material, and the positive electrode active material has a powder compaction density of 2.40 g / cm3 or more under a pressure of 29400 N. 3 -2.65 g / cm3 3 .

[0068] In any embodiment, the positive electrode active material has a gram capacity of 135 mAh / g-150 mAh / g at 40℃ and 1 / 3C discharge rate.

[0069] In any embodiment, 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).

[0070] In any embodiment, the single-side coating weight of the positive electrode film layer is 300 mg / 1540 mm 2 -580 mg / 1540 mm 2 .

[0071] In any embodiment, the positive electrode film layer has a compaction density of 2.25 g / cm3 or more. 3 -2.75 g / cm3 3 .

[0072] A second aspect of the present application provides a power utilization device comprising the secondary battery of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0073] FIG. 1 is a longitudinal sectional view of a positive electrode sheet according to an embodiment of the present application;

[0074] FIG. 2 is a transmission electron microscope image of particles of a positive electrode film layer according to Example 1 of the present application;

[0075] FIG. 3 is a schematic view of a secondary battery according to an embodiment of the present application;

[0076] FIG. 4 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 3;

[0077] FIG. 5 is a schematic view of a battery module according to an embodiment of the present application;

[0078] FIG. 6 is a schematic view of a battery pack according to an embodiment of the present application;

[0079] FIG. 7 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 6;

[0080] FIG. 8 is a schematic view of a power utilization device using the secondary battery according to an embodiment of the present application as a power source;

[0081] FIG. 9 is a charge-discharge curve of a secondary battery in Example 11 of the present application at 40°C, 1 / 3C charge-discharge rate;

[0082] FIG. 10 is a charge-discharge curve of a secondary battery in Comparative Example 1 of the present application at 40°C, 1 / 3C charge-discharge rate.

[0083] Reference signs: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate; 10 positive electrode tab; 110 positive electrode current collector; 120 positive electrode film layer; 1210 first type of particle; 1220 second type of particle. DETAILED DESCRIPTION

[0084] Hereinafter, specific embodiments of the secondary battery and the power consuming device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters well known, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0085] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. 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 contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained in the range between "a" and "b," wherein "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0086] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0087] If not particularly specified, all the technical features and optional technical features in the present application can be combined with each other to form new technical solutions.

[0088] If not particularly specified, all the steps in the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0089] If not particularly specified, the "comprise" and "include" mentioned in the present application are open-ended, and can also be closed. For example, the "comprise" and "include" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0090] If not particularly specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": 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 A and B are both true (or exist).

[0091] The positive active material is one of the decisive factors of the performance of the secondary battery. At present, the common positive active materials mainly include lithium cobaltate, lithium manganate, nickel-cobalt-manganese ternary material and lithium iron phosphate, etc. These materials have advantages and disadvantages respectively. For example, lithium cobaltate has high energy density and voltage platform, but high cost and poor safety; lithium manganate has low cost and good safety, but low energy density and voltage platform; nickel-cobalt-manganese ternary material combines the advantages of the former two, but the cost is still high. Lithium iron phosphate has the advantages of low cost, high safety and long life, and 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 tap density and low discharge capacity, which limit its application in high energy density batteries. Lithium manganese iron phosphate, as a new type of material developed from lithium iron phosphate, combines the advantages of manganese and iron elements, has two voltage platforms at 4.1V and 3.4V respectively, and can provide certain platform capacity, which is expected to improve the disadvantages of lithium iron phosphate material. However, in the current research and application process, lithium manganese iron phosphate still has low tap density and does not show the potential advantage of high energy density. At the same time, the existence of manganese element also affects the conductivity of lithium manganese iron phosphate, affects the capacity and kinetic performance of the material, affects the rate performance and energy density of the battery, and limits its further application and development. Therefore, how to improve the tap density of lithium manganese iron phosphate and obtain high energy density battery while considering the rate performance of the battery has become a key point of research.

[0092] [Secondary battery]

[0093] Based on this, the application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte,

[0094] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector.

[0095] The positive electrode film layer comprises first particles and second particles, and the first particles and the second particles comprise lithium-containing transition metal phosphate materials.

[0096] The primary particle size of the first particles is greater than 180 nm and less than 900 nm, and the primary particle size of the second particles is greater than or equal to 900 nm and less than or equal to 5 microns.

[0097] The average value of the Mn molar ratio of the second particles is less than the average value of the Mn molar ratio of the first particles.

[0098] The Mn molar ratio refers to the ratio of the number of moles of Mn to the total number of moles of Mn and Fe.

[0099] As shown in the longitudinal sectional view of the positive electrode tab, the positive electrode tab 10 includes a positive electrode current collector 110 and a positive electrode film layer 120 disposed on at least one side of the positive electrode current collector, the positive electrode film layer including first type particles 1210 and second type particles 1220.

[0100] In the present text, the term "primary particle size" refers to the particle size of primary particles.

[0101] Primary particles refer to the single particles that can be distinguished after the transmission electron microscopy (TEM) images of the particles are recognized by general professional software (for example, spectrum see; Avizo 3D) and confirmed, or that can be distinguished after artificial recognition or artificial aided calibration. Specifically, in order to determine the primary particles, the particles contained in the positive electrode film layer are subjected to enrichment and / or dispersion treatment, and then imaged under a transmission electron microscope. The imaged picture can be directly subjected to particle recognition by software (according to parameters such as gray scale and / or contrast / brightness), and the single particles that can be distinguished after recognition are primary particles. The imaged picture can also be directly subjected to artificial recognition, and the single particles that can be distinguished after recognition are primary particles. The imaged picture can also be directly subjected to software recognition combined with artificial aided calibration recognition, and the single particles that can be distinguished after recognition are primary particles. More specifically, the particles in the transmission electron microscope field of view form particles with clear boundaries that can be clearly distinguished from each other, and the single particles can be directly confirmed by software recognition or artificial recognition. However, some particles may be adhered and stacked to a certain extent in the transmission electron microscope field of view after dispersion treatment. For the adhered and stacked particles, the single particles that can be distinguished after recognition by software (according to parameters such as gray scale / contrast / brightness) are counted as primary particles. More accurately, for the particles that are adhered and stacked to a certain extent in the transmission electron microscope field of view, the single particles that can be distinguished after recognition by software according to parameters such as gray scale / contrast / brightness are subjected to artificial aided calibration according to certain rules by artificial recognition, and the single particles that can be distinguished after calibration are counted as primary particles. If the artificial calibration results are not uniform, the results obtained by 3 or 5 or 7 persons who are unaware of each other and separately calibrate the same imaging results according to the rules exemplified below are counted as the number of primary particles. The transmission electron microscopy images of the particles of the positive electrode film layer in Example 1 in FIG. 2 are taken as an example to further illustrate the distinction in the primary particle number and area statistical process. FIG. 2-a is the original transmission electron microscopy image, FIG. 2-b is the software recognition image of the image, and FIG. 2-c is an example of software recognition and / or artificial recognition of the independent particles, adhered particles and stacked particles in FIG. 2-a. The particles 1 and 2 in FIG. 2-c are distinguishable independent particles, which are primary particle 1 and primary particle 2, respectively. The particles 3 and 4 in FIG. 2-c are adhered, and the particles 5, 6 and 7 are adhered. After software recognition or artificial recognition, they are determined to be primary particle 3, primary particle 4, primary particle 5, primary particle 6 and primary particle 7. The particles 8 and 9 stacked together are finally determined to be primary particle 8 and primary particle 9, instead of being determined to be one particle. FIG. 2-d is another example of software recognition and / or artificial recognition of the particles with stacking in FIG. 2-a. The particles 10-14 stacked together are finally determined to be primary particle 10, 11, 12, 13 and primary particle 14, instead of being determined to be one particle.In selecting the transmission electron microscope field of view, the number of stacked particles in the selected field of view accounts for less than 20% of the total number of particles (the total number of independent particles, adhered particles and stacked particles), more preferably the number of stacked particles in the selected field of view accounts for less than 15% of the total number of particles (the total number of independent particles, adhered particles and stacked particles), and further preferably the number of stacked particles in the selected field of view accounts for less than 10% of the total number of particles (the total number of independent particles, adhered particles and stacked particles).

[0102] The test method for the average value of the Mn molar percentage of the first type of particles and the average value of the Mn molar percentage of the second type of particles can be performed by methods and equipment known in the art, for example as follows: disassemble the battery to obtain a positive electrode sheet, peel off the positive electrode film layer of the positive electrode sheet, wash the positive electrode film layer thoroughly with acetone to remove the binder and dispersant and the like in the positive electrode film layer, filter and dry to obtain a powder. 0.05 g of the uniformly mixed powder is dissolved in 40 ml of anhydrous ethanol, then an appropriate amount of dispersant is added, and the mixture is stirred uniformly to obtain a suspension. 2 ml of the suspension and 2 ml of anhydrous ethanol are mixed and then subjected to ultrasonic treatment, with an ultrasonic power of 480 W and an ultrasonic time of 5 min, to obtain a uniformly dispersed suspension. An appropriate amount of the middle layer of the suspension is subjected to transmission electron microscopy testing, and the projected area of each primary particle in the transmission electron microscopy image is counted according to the definition of the primary particle described above, i.e. the cross-sectional area S of the primary particle, and the equivalent circle diameter of the primary particle is obtained by the equivalent circle method, i.e. the primary particle size d of the primary particle. In the above process of counting the primary particles and their primary particle sizes, primary particles with a primary particle size less than 50 nm and greater than 5 μm are not included in the statistical range (i.e. primary particles with a primary particle size greater than or equal to 50 nm and less than or equal to 5 μm are effective particles). The molar contents of Mn and Fe in each effective particle in the transmission electron microscopy image can be tested by EDS point scanning, i.e. the molar percentage X of Mn in each effective particle can be calculated (the molar percentage of Mn refers to the molar content of Mn relative to the total molar content of Mn and Fe), and the test point is the middle part of the transmission surface of each particle. The transmission electron microscopy and EDS testing in different test areas are performed multiple times, and the cross-sectional area S, the primary particle size d and the molar percentage X of Mn of at least 500 effective particles are tested. The effective particles obtained by testing are then numbered 1, 2, 3, 4, 5…n in order of increasing primary particle size, and the total number of particles is n. The mth particle is a particle with a primary particle size less than or equal to 180 nm, the m+1th particle is a particle with a primary particle size greater than 180 nm, the k-1th particle is a particle with a primary particle size less than 900 nm, and the kth particle is a particle with a primary particle size greater than or equal to 900 nm. The m+1th to k-1th particles are the first type of particles, and the kth to nth particles are the second type of particles. When the primary particle size of the particle numbered 1 is greater than 180 nm, i.e. the particle numbered 1 to the k-1th particle are the first type of particles, and the kth to nth particles are the second type of particles, then m is 0. The calculation formula for the average value of the Mn molar percentage of the first type of particles is

[0103] The calculation formula for the average value of the Mn molar percentage of the second type of particles is

[0104] wherein Xi represents the Mn molar percentage of the particle numbered i, and Si represents the cross-sectional area of the particle numbered i.

[0105] The positive electrode active material includes two types of particles with different primary particle sizes, which can realize the purpose of filling gaps by the cooperation of large and small particles, so that the particle accumulation in the positive electrode active material is more compact, the powder compaction density of the material and the compaction density of the electrode sheet are improved, and the energy density of the battery is improved. However, the second type of particles has a relatively large primary particle size, which makes the migration path of lithium ions in the particles longer, resulting in an increase in the discharge polarization of the second type of particles and a decrease in the specific capacity, affecting the specific capacity and kinetic performance of the material, and further affecting the energy density and rate performance of the battery. The Mn molar ratio of the particles affects the conductivity of the particles. By controlling the average value of the Mn molar ratio of the second type of particles with a relatively large primary particle size to be less than the average value of the Mn molar ratio of the first type of particles with a relatively small primary particle size, the conductivity of the second type of particles with a relatively large primary particle size can be improved, the discharge polarization of the second type of particles can be alleviated, the specific capacity and kinetic performance of the material can be improved, and the energy density and rate performance of the battery can be improved. At the same time, the Mn molar ratio in the first type of particles with a relatively small primary particle size is relatively high, which can improve the platform capacity of the first type of particles while maintaining good conductivity of the particles, and is beneficial to improving the energy density of the battery.

[0106] In summary, the positive electrode film layer contains the first type of particles with a primary particle size greater than 180 nm and less than 900 nm and the second type of particles with a primary particle size greater than or equal to 900 nm and less than or equal to 5 μm, and the average value of the Mn molar ratio of the second type of particles with a relatively large particle size is less than the average value of the Mn molar ratio of the first type of particles with a relatively small particle size. This can improve the powder compaction density and specific capacity of the material, improve the energy density of the battery, and also improve the conductivity of the material and the rate performance of the battery.

[0107] In some embodiments, the molar percentage of Mn in the second type of particles based on the total number of moles of Mn in the primary particles of the positive electrode film layer is 0%-50%, optionally 0%-30%, optionally 0%-10%, and more optionally 0%.

[0108] In some embodiments, the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, can be 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.75%, 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.

[0109] The method for testing the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, can be performed by methods and devices known in the art, for example as follows: referring to the aforementioned method for testing the average value of the mole percentage of Mn in the second type of particles, the cross-sectional area S and the mole percentage of Mn X of each particle are determined,

[0110] and the calculation formula for the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, is:

[0111] wherein Xi, Xj represent the mole percentage of Mn of particles numbered i, j, and Si, Sj represent the cross-sectional area of particles numbered i, j, respectively.

[0112] Controlling the mole percentage of Mn in the second type of particles within a suitable range can further improve the conductivity of the second type of particles, alleviate the discharge polarization of the second type of particles, be conducive to further improving the rate performance of the battery, and at the same time be conducive to concentrating sufficient manganese elements in the first type of particles with small primary particle size, so that the first type of particles contribute more platform capacity, improve the energy density of the battery, and be suitable for high-rate and high-energy-density batteries.

[0113] In some embodiments, the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, is 5%-50%, can be 5%-30%, can be more 5%-10%, and can be further 5%.

[0114] In some embodiments, the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, can be 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 aforementioned values.

[0115] Distributing a small amount of Mn in the second type of particles can alleviate the influence of Mn dissolution phenomenon on the cycle performance and storage performance of the battery caused by excessive Mn concentrating in the first type of particles with relatively small primary particle size, while improving the energy density of the battery, and also taking into account certain cycle performance and storage performance, so that the battery is more suitable for application scenarios with certain demands for cycle performance and / or storage performance.

[0116] In some embodiments, the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, is 10%-50%, which can be 10%-30%, and more preferably 10%.

[0117] In some embodiments, the mole percentage of Mn in the second type of particles, based on the total moles of Mn in primary particles of the positive electrode film layer, can be 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 aforementioned values.

[0118] Controlling the mole percentage of Mn in the second type of particles within a suitable range can further alleviate the influence of Mn dissolution phenomenon on the cycle performance and storage performance of the battery caused by excessive Mn concentrating in the first type of particles with relatively small primary particle size, while the second type of particles has good electrical conductivity, so that the battery is more suitable for application scenarios with high demands for storage performance and / or cycle performance.

[0119] In some embodiments, the ratio of the average value of the mole fraction of Mn of the second type of particles to the average value of the mole fraction of Mn of the first type of particles is 0-0.8, optionally 0-0.5, more optionally 0.

[0120] In some embodiments, the ratio of the average value of the mole fraction of Mn of the second type of particles to the average value of the mole fraction of Mn of the first type of particles is optionally 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, 0.65, 0.7, 0.75, 0.8, or a range between any two of the aforementioned values.

[0121] Controlling the ratio of the average value of the mole fraction of Mn of the second type of particles to the average value of the mole fraction of Mn of the first type of particles within a suitable range can improve the conductivity of the second type of particles while achieving the purpose of the first type of particles contributing to high platform capacity, thereby comprehensively improving the energy density and rate performance of the battery, making the battery suitable for use in scenarios with high demand for rate performance and / or energy density.

[0122] In some embodiments, the ratio of the average value of the mole fraction of Mn of the second type of particles to the average value of the mole fraction of Mn of the first type of particles is 0.0003-0.8, optionally 0.0003-0.5, more optionally 0.0003.

[0123] In some embodiments, the ratio of the average value of the mole fraction of Mn of the second type of particles to the average value of the mole fraction of Mn of the first type of particles is optionally 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, 0.65, 0.7, 0.75, 0.8, or a range between any two of the aforementioned values.

[0124] The average value of the Mn molar ratio of the second type of particles is greater than 0 than the average value of the Mn molar ratio of the first type of particles, so that the second type of particles have a certain amount of Mn element, the second type of particles can contribute a certain platform capacity, which is beneficial to improve the energy density of the battery, and at the same time can alleviate the influence of the Mn dissolution phenomenon caused by too much Mn concentrated in the first type of particles with relatively small primary particle size on the cycle performance and storage performance of the battery, so that the battery is more suitable for application scenarios with certain demands for cycle performance and / or storage performance.

[0125] In some embodiments, the ratio of the average value of the Mn molar ratio of the second type of particles to the average value of the Mn molar ratio of the first type of particles is 0.002-0.8, which can be 0.002-0.5, and more preferably 0.002.

[0126] In some embodiments, the ratio of the average value of the Mn molar ratio of the second type of particles to the average value of the Mn molar ratio of the first type of particles can be 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 a range between any two of the above values.

[0127] The ratio of the average value of the Mn molar ratio of the second type of particles to the average value of the Mn molar ratio of the first type of particles in a suitable range can further alleviate the influence of the Mn dissolution phenomenon caused by too much Mn concentrated in the first type of particles with relatively small primary particle size on the cycle performance and storage performance of the battery, so that the battery is more suitable for application scenarios with high demands for storage performance and / or cycle performance.

[0128] In some embodiments, the average value of the Mn molar ratio of the first type of particles is 0.4-0.9, which can be 0.5-0.9. In some embodiments, the average value of the Mn molar ratio of the first type of particles can be 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or a range between any two of the above values.

[0129] Controlling the average value of the Mn molar ratio of the first type of particles in a suitable range makes the first type of particles have high platform capacity, while also ensuring that the first type of particles have certain electrical conductivity, which is beneficial to the first type of particles to exert its specific capacity and platform capacity, achieve the purpose of the first type of particles to provide capacity, and improve the energy density of the battery.

[0130] In some embodiments, the average value of the mole fraction of Mn of the second type of particles is 0-0.6, optionally 0-0.5, more optionally 0-0.1, further optionally 0.

[0131] In some embodiments, the average value of the mole fraction of Mn of the second type of particles is optionally 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or a range between any two of the aforementioned values.

[0132] Controlling the average value of the mole fraction of Mn of the second type of particles in a suitable range can improve the conductivity of the second type of particles, improve the conductivity of the overall material, and improve the rate performance of the battery.

[0133] In some embodiments, the average value of the mole fraction of Mn of the second type of particles is 0.02-0.6, optionally 0.02-0.2, more optionally 0.02.

[0134] In some embodiments, the average value of the mole fraction of Mn of the second type of particles is optionally 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or a range between any two of the aforementioned values.

[0135] Controlling the average value of the mole fraction of Mn of the second type of particles to be greater than 0 can improve the conductivity of the second type of particles and the material, and also enable the second type of particles to have a certain plateau capacity and high gravimetric capacity, thereby further improving the energy density of the battery.

[0136] In some embodiments, the average value of the mole fraction of Mn of the second type of particles is 0.1-0.3, optionally 0.1.

[0137] In some embodiments, the average value of the mole fraction of Mn of the second type of particles is optionally 0.1, 0.15, 0.2, 0.25, 0.3, or a range between any two of the aforementioned values.

[0138] The average value of the Mn molar ratio of the second type of particles is within a suitable range, which enables the second type of particles to have good electrical conductivity while providing relatively more voltage platforms and specific capacity, thereby further improving the energy density of the battery and making it more suitable for use in scenarios with high energy density requirements.

[0139] In some embodiments, the area ratio of the first type of particles is 20%-95%, optionally 20%-80%, more optionally 40%-60%, and / or the area ratio of the second type of particles is 5%-80%, optionally 15%-80%, more optionally 25%-60%, based on the total area of primary particles of the positive electrode film layer.

[0140] In some embodiments, the area ratio of the first type of particles is optionally 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range between any two of the above values, based on the total area of primary particles of the positive electrode film layer.

[0141] In some embodiments, the area ratio of the second type of particles is optionally 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range between any two of the above values, based on the total area of primary particles of the positive electrode film layer.

[0142] The testing method for the area ratio of the first type of particles and the area ratio of the second type of particles can be performed by methods and equipment known in the art, for example as follows: referring to the aforementioned testing method for determining 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 calculation formula for the area ratio of the first type of particles is:

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

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

[0146] The area ratio of the first type of particles and the area ratio of the second type of particles are within suitable ranges, which enables the gradation of large and small particles, improves the powder compaction density of the material and the compaction density of the electrode sheet, and also enables the first type of particles with relatively high Mn content to provide platform capacity, and reduces the impact of the second type of particles with large particle size on the electrical conductivity of the material, which is conducive to obtaining a battery with high energy density and excellent rate performance.

[0147] In some embodiments, the positive electrode film layer comprises third type of particles, the third type of particles comprising the lithium-containing transition metal phosphate material, the primary particle size of the third type of particles being 50 nm-180 nm,

[0148] wherein the area ratio of the third type of particles is greater than or equal to 5% and less than or equal to 30% based on the total area of the primary particles of the positive electrode film layer.

[0149] In this context, the third type of particles is a primary particle.

[0150] The determination of the third type of particles and the testing method of the area ratio thereof can be performed by methods and devices known in the art, for example as follows: referring to the testing method of the average value of the Mn molar ratio of the second type of particles as described above, defining the first particle to the mth particle as the third type of particles, the calculation formula of the area ratio of the third type of particles is

[0151] wherein Si and Sj represent the cross-sectional area of the particles numbered i and j respectively.

[0152] In some embodiments, the area ratio of 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%, or a range between any two of the above values, based on the total area of the primary particles of the positive electrode film layer.

[0153] The third type of particles with a smaller primary particle size and a suitable area ratio can be filled into the pores between the first type of particles and the second type of particles, so that the filling between the materials is more compact, which can further improve the powder compaction density of the material and is beneficial to obtain a high-energy-density battery.

[0154] In some embodiments, the average value of the Mn molar ratio of the third type of particles is less than the average value of the Mn molar ratio of the first type of particles.

[0155] The testing method of the average value of the Mn molar ratio of the third type of particles refers to the testing method of the average value of the Mn molar ratio of the second type of particles,

[0156] The calculation formula of the average value of the Mn molar ratio of the third type of particles is

[0157] wherein Xi represents the Mn molar ratio of the particle numbered i, and Si represents the cross-sectional area of the particle numbered i.

[0158] As mentioned above, ultra-small particle size type III particles can further improve the powder compaction density of materials. However, ultra-small particle size type III particles have a large specific surface area and significantly increased surface activity. They are more likely to come into contact with electrolyte and undergo side reactions, exacerbating manganese dissolution and thus affecting the storage performance and cycle performance of the battery.

[0159] By controlling the average molar percentage of Mn in the third type of particles to be less than the average molar percentage of Mn in the first type of particles, it is beneficial to reduce the side reactions between the third type of particles and the electrolyte and the degree of manganese dissolution. This not only improves the energy density of the battery, but also enhances its cycle performance and storage performance, and extends its service life.

[0160] 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%-12%, optionally 0%-8%, optionally 0%-6%, and more preferably 0%.

[0161] 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 optionally 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 a range between any two of the above values.

[0162] Based on the total number of moles of Mn in the primary particles of the positive electrode film, the method for testing 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 method for testing the average molar percentage of Mn in the second type of particles, the cross-sectional area S and the molar percentage X of Mn for each particle are determined.

[0163] 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:

[0164] 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.

[0165] By controlling the molar percentage of Mn in the third type of particles within a suitable range, the possibility of side reactions between the third type of particles and the electrolyte and the occurrence of manganese dissolution can be reduced, thereby improving the cycle performance and storage performance of the battery, extending the battery's lifespan and storage life, and making the battery suitable for application scenarios with high requirements for cycle life and / or storage life.

[0166] In some embodiments, the mole percentage of Mn in the third type of particles is 0.02%-12%, optionally 0.02%-8%, more optionally 0.02%-6%, further optionally 0.02%, based on the total moles of Mn in primary particles of the positive electrode film layer.

[0167] In some embodiments, the mole percentage of Mn in the third type of particles is 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, based on the total moles of Mn in primary particles of the positive electrode film layer.

[0168] Controlling the mole percentage of Mn in the third type of particles to be greater than 0 allows the small-particle-diameter third type of particles to have a certain amount of Mn element, which is conducive to the third type of particles with high electrical conductivity to fully exert their gram capacity, and further improves the energy density of the battery, and the battery is more suitable for scenarios with certain demands for energy density.

[0169] In some embodiments, the mole percentage of Mn in the third type of particles is 0.2%-12%, optionally 0.2%-8%, more optionally 0.2%-6%, further optionally 0.2%, based on the total moles of Mn in primary particles of the positive electrode film layer.

[0170] In some embodiments, the mole percentage of Mn in the third type of particles is optionally 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, based on the total moles of Mn in primary particles of the positive electrode film layer.

[0171] Controlling the mole percentage of Mn in the third type of particles to be within a suitable range allows the small-particle-diameter third type of particles to have a relatively large amount of Mn element, which is conducive to the third type of particles with high electrical conductivity to fully exert their gram capacity, and further improves the energy density of the battery, and the battery is more suitable for scenarios with high demands for energy density.

[0172] In some embodiments, the ratio of the average value of the mole percentage of Mn in the third type of particles to the average value of the mole percentage of Mn in the first type of particles is 0-0.8, optionally 0-0.4, more optionally 0.

[0173] In some embodiments, the ratio of the average value of the Mn molar percentage of the third type of particles to the average value of the Mn molar percentage of the first type of particles can be 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 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.

[0174] Controlling the ratio of the average value of the Mn molar percentage of the third type of particles to the average value of the Mn molar percentage of the first type of particles within a suitable range can improve the cycle stability and storage stability of the third type of particles, while achieving the purpose of the platform capacity contributed by the first type of particles, and comprehensively improving the energy density, storage performance and cycle performance of the battery.

[0175] In some embodiments, the ratio of the average value of the Mn molar percentage of the third type of particles to the average value of the Mn molar percentage of the first type of particles is 0.0003-0.8, which can be 0.0003-0.4, and more preferably 0.0003.

[0176] In some embodiments, the ratio of the average value of the Mn molar percentage of the third type of particles to the average value of the Mn molar percentage of the first type of particles can be 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, 0.65, 0.7, 0.75, 0.8, or a range between any two of the above values.

[0177] The average value of the Mn molar ratio of the third type of particles is controlled to be within a suitable range from the average value of the Mn molar ratio of the first type of particles, so that the third type of particles has a certain amount of Mn content, and the third type of particles with excellent electrical conductivity can fully exert its gram capacity, which is beneficial to improve the energy density of the battery, so that the battery is more suitable for use scenarios with certain energy density requirements.

[0178] In some embodiments, the ratio of the average value of the Mn molar ratio of the third type of particles to the average value of the Mn molar ratio of the first type of particles is 0.002-0.8, optionally 0.002-0.4, and more optionally 0.002.

[0179] In some embodiments, the ratio of the average value of the Mn molar ratio of the third type of particles to the average value of the Mn molar ratio of the first type of particles is optionally 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 a range between any two of the above values.

[0180] The average value of the Mn molar ratio of the third type of particles is controlled to be within a suitable range from the average value of the Mn molar ratio of the first type of particles, so that the third type of particles has a relatively large amount of Mn content, and the third type of particles with excellent electrical conductivity can fully exert its gram capacity, which is beneficial to improve the energy density of the battery, so that the battery is more suitable for use scenarios with high energy density requirements.

[0181] In some embodiments, the average value of the Mn molar ratio of the third type of particles is 0-0.6, optionally 0-0.4, optionally 0-0.2, and more optionally 0.

[0182] In some embodiments, the average value of the mole fraction of Mn of the third type of particles can be 0, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or a range between any two of the above values.

[0183] Controlling the average value of the mole fraction of Mn of the third type of particles within a suitable range can reduce the possibility of side reactions and manganese dissolution of the third type of particles with the electrolyte, improve the cycle stability and storage stability of the third type of particles, and improve the cycle performance and storage performance of the battery.

[0184] In some embodiments, the average value of the mole fraction of Mn of the third type of particles is 0.02-0.6, which can be 0.02-0.4, and more preferably 0.02-0.2, and further preferably 0.02.

[0185] In some embodiments, the average value of the mole fraction of Mn of the third type of particles can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.50, 0.55, 0.6, or a range between any two of the above values.

[0186] Controlling the average value of the mole fraction of Mn of the third type of particles to be greater than 0 allows the third type of particles with excellent electrical conductivity to fully exert their specific capacity, which can further improve the energy density of the battery, making the battery more suitable for use in scenarios with certain energy density requirements.

[0187] In some embodiments, the average value of the mole fraction of Mn of the third type of particles is 0.1-0.2, which can be 0.1.

[0188] In some embodiments, the average value of the mole fraction of Mn of the third type of particles can be 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, or a range between any two of the above values.

[0189] The average of the Mn molar ratio of the third type of particles is controlled within a suitable range, so that the third type of particles with excellent electrical conductivity can fully play their capacity, further improving the energy density of the battery, making the battery more suitable for use in scenarios with high energy density requirements.

[0190] In some embodiments, the area ratio of the first type of particles is 45%-85%, the area ratio of the second type of particles is 10%-40%, and the area ratio of the third type of particles is 5%-15%, based on the total area of primary particles of the positive electrode film layer.

[0191] In some embodiments, the area ratio of the first type of particles can be 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, based on the total area of primary particles of the positive electrode film layer.

[0192] In some embodiments, the area ratio of the second type of particles can be 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 a range between any two of the above values, based on the total area of primary particles of the positive electrode film layer.

[0193] In some embodiments, the area ratio of the third type of particles can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two of the above values, based on the total area of primary particles of the positive electrode film layer.

[0194] Controlling the area ratio of particles of different particle sizes within a suitable range can achieve the purpose of the contribution of the flat capacity of the first type of particles with high manganese content to the energy density, while also reducing the impact of the second type of particles with large particle size on the rate performance of the battery and reducing the impact of the third type of particles with small particle size on the storage performance of the battery, with high energy density, good storage performance, and rate performance.

[0195] In some embodiments, the average value of the Mn molar percentage of the primary particles of the positive electrode film layer is 0.2-0.9, which can be 0.4-0.8.

[0196] In some embodiments, the average value of the Mn molar percentage of the primary particles of the positive electrode film layer can be 0.2, 0.3, 0.4, 0.45, 0.50, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.9, or a range between any two of the above values.

[0197] The average value of the Mn molar percentage of the primary particles of the positive electrode film layer can be determined by methods and devices known in the art, for example as follows: referring to the aforementioned test method for determining the average value of the 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,

[0198] The calculation formula of the average value of the Mn molar percentage of the primary particles of the positive electrode film layer is

[0199] wherein Xi represents the Mn molar percentage of the particle numbered i, and Si represents the cross-sectional area of the particle numbered i.

[0200] Controlling the average value of the Mn molar percentage in the whole particles within a suitable range, the material has high specific capacity, excellent cycle stability, storage stability and conductivity, which is beneficial to obtain a battery with high energy density, excellent cycle performance, storage performance and rate performance.

[0201] In some embodiments, the particle size distribution index of the primary particle size of the first type of particles is greater than 0 and less than or equal to 0.5,

[0202] The particle size distribution index refers to the ratio of the standard deviation of the primary particle size of the first type of particles to the average primary particle size of the first type of particles.

[0203] In some embodiments, the particle size distribution index of the primary particle size of the first type of particles can be 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.

[0204] The test method for the particle size distribution index of the primary particle size of the first type of particles is performed by methods and devices known in the art, for example as follows: referring to the aforementioned test method for determining the average value of the Mn molar percentage of the second type of particles, the primary particle size of each particle in the first type of particles is determined,

[0205] The particle size distribution index PDI is the standard deviation σ of the particle size divided by the average particle size

[0206] wherein σ is the standard deviation of the particle size, x i is the primary particle size of each particle in the first type of particles, is the primary average particle size of the first type of particles, n is the total number of particles of the first type of particles in the statistics, and the average particle size is the total primary particle size value of the first type of particles divided by the total number of particles of the first type of particles in the statistics.

[0207] By controlling the particle size distribution index of the primary particle size of the first type of particles within a suitable range, the discharge behavior of each particle in the first type of particles in the battery cycle process can be improved to be consistent, the possibility of overcharge and overdischarge of each particle in the charge and discharge process is reduced, and the structural stability of the material is improved, and the cycle performance of the battery is improved.

[0208] In some embodiments, the composition general formula of the lithium-containing transition metal phosphate material of the first type of particles includes Li m1 A1 a1 Fe x1 Mn y1 M1 b1 P z1 Q1 c1 O n1 N1 d1 ,

[0209] 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,

[0210] The composition general formula of the lithium-containing transition metal phosphate material of the second 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,

[0211] The composition general formula of the lithium-containing transition metal phosphate material of the third type of particles includes Li m3 A3 a3Fe x3 Mn y3 M3 b3 P z3 Q3 c3 O n3 N2 d3 ,

[0212] 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,

[0213] 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.

[0214] In some embodiments, m1, m2, and m3 each independently can 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 number in a range between any two of the foregoing values.

[0215] In some embodiments, x1+y1, x2+y2, and x3+y3 each independently can 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 number in a range between any two of the foregoing values.

[0216] In some embodiments, z1, z2, or z3 each independently can be 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, or a number in a range between any two of the foregoing values.

[0217] In some embodiments, n1, n2, and n3 each independently can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, or a number in a range between any two of the foregoing values.

[0218] In some embodiments, 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 in a range between any two of the foregoing.

[0219] By selecting appropriate modification elements M1, M2, M3, the lattice change rate of the material during lithium extraction can be improved, the structural stability of the material can be improved, the dissolution of manganese can be reduced, and the oxygen activity on the surface of the particles can be reduced, thereby improving the specific capacity of the material, improving the energy density of the battery, and reducing the interface side reaction between the material and the electrolyte during use, thereby improving the cycle performance and storage performance of the material.

[0220] By selecting appropriate modification elements Q1, Q2, Q3, the difficulty of changing the Mn-O bond length can be changed, thereby improving the electronic conductivity and reducing the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance of the secondary battery.

[0221] By selecting appropriate modification elements A1, A2, A3, the lattice change rate of the material can also be improved, and the battery capacity of the material can be maintained.

[0222] Modification elements N1, N2, N3 can help to improve the interface side reaction between the material and the electrolyte, reduce the interface activity, thereby improving the cycle performance of the positive electrode active material, etc. In addition, the performance of the material in resisting acid corrosion such as HF can also be improved, thereby improving the cycle performance and storage life of the material.

[0223] In this document, modification elements M1, M2, M3, Q1, Q2, Q3, A1, A2, A3, N1, N2, N3 can exist in the lithium-containing transition metal phosphate material in the form of doping elements, and can also exist in the coating layer of the material in the form of coating elements.

[0224] In some embodiments, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises the lithium-containing transition metal phosphate material, and the powder compaction density of the positive electrode active material under a pressure of 29400 N is 2.40 g / cm3 3 - 2.65 g / cm3 3 .

[0225] In some embodiments, the positive electrode active material comprises 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 2.40 g / cm3 3 , 2.41 g / cm3 3 , 2.42 g / cm3 3 , 2.43 g / cm3 3 , 2.44 g / cm3 32.45 g / cm3 3 2.46 g / cm3 3 2.47 g / cm3 3 2.48 g / cm3 3 2.49 g / cm3 3 2.50 g / cm3 3 2.51 g / cm3 3 2.52 g / cm3 3 2.53 g / cm3 3 2.54 g / cm3 3 2.55 g / cm3 3 2.56 g / cm3 3 2.57 g / cm3 3 2.58 g / cm3 3 2.59 g / cm3 3 2.60 g / cm3 3 2.61 g / cm3 3 2.62 g / cm3 3 2.63 g / cm3 3 2.64 g / cm3 3 2.65 g / cm3 3 or a range between any two of the above values.

[0226] The powder compaction density of the positive active material under a pressure of 29400 N can be carried out by methods and devices known in the art, for example as follows: place the battery in a 25°C oven environment, stand for 2 h, and when the battery temperature is maintained at 25°C, discharge the battery at 1 / 3C constant current to 2.0 V, disassemble the battery, obtain the positive electrode sheet, peel off the positive electrode film layer, and wash thoroughly with acetone to remove the binder in the positive electrode film layer; dry to obtain powder for subsequent characterization test. The subsequent characterization can refer to GB / T 24533-2009, and is measured by a compaction density instrument. Specifically, a certain amount of the above prepared powder is placed on a compaction special mold (the mold diameter is known), and the mold has a metal disc on each of the upper and lower hollow centers. 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 29400 N. The thickness of the powder under a pressure of 29400 N can be read on the device, and then the powder compaction density of the material is calculated as p = m / v, where v = (S x 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 device model of the compaction density instrument is UTM7305, and the device manufacturer is Sanechips.

[0227] The greater the powder compaction density, the higher the mass of the powder material in a unit volume. When the powder compaction density of the material is in a suitable range, the positive electrode sheet has a higher compaction density during cold pressing, which is beneficial to further improving the volume energy density of the battery.

[0228] In some embodiments, the gram capacity of the positive electrode active material at 40℃ and 1 / 3C discharge rate is 135mAh / g-150mAh / g. In some embodiments, the gram capacity of the positive electrode active material at 40℃ and 1 / 3C discharge rate can be selected as 135mAh / g, 140mAh / g, 145mAh / g, 150mAh / g, or a range between any two of the above values.

[0229] The gram capacity of the positive electrode active material can be measured by methods and devices known in the art, for example as follows: place the battery in a 40℃ oven environment and stand for 2h until the battery temperature is maintained at 40℃; then discharge the battery at 1 / 3C constant current to 2.0V; stand for 5min; after charging the battery to 4.1V at 1 / 3C constant current, charge the battery to the cutoff current of 0.05C at 4.1V constant voltage; stand for 5min; discharge the battery at 1 / 3C constant current 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 to obtain a positive electrode sheet with an area of S2, separate the positive electrode film layer on the positive electrode sheet from the current collector, and then dissolve it in acetone, wash thoroughly to remove residual solvents and binders, and then filter, dry and obtain a sample powder. The weight of the sample powder is M2, and the total mass M1 of the positive electrode active material of the battery is approximately M2*(S1 / S2). The gram capacity of the positive electrode active material is equal to the discharge capacity C of the battery / the mass M1 of the positive electrode active material.

[0230] [Preparation method of positive electrode active material]

[0231] The application also provides a preparation method of a positive electrode active material:

[0232] mixing the first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material to obtain a lithium-containing transition metal phosphate material,

[0233] The first lithium-containing transition metal phosphate material comprises a first inner core and a first carbon coating layer coated on the outer surface of the first inner core, and the second lithium-containing transition metal phosphate material comprises a second inner core and a second carbon coating layer coated on the outer surface of the second inner core,

[0234] The primary average particle size of the first lithium-containing transition metal phosphate material is smaller than the primary average particle size of the second lithium-containing transition metal phosphate material,

[0235] The Mn molar ratio of the second lithium-containing transition metal phosphate material is less than the Mn molar ratio of the first lithium-containing transition metal phosphate material,

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

[0237] The primary average particle size of the second lithium-containing transition metal phosphate material is 250 nm to 4000 nm.

[0238] The test method of the Mn molar ratio of the first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material can be performed by methods and devices known in the art, for example, as follows: the molar contents of Mn and Fe elements are tested according to the chemical analysis method for nanometer lithium iron phosphate in the national standard GB T33822-2017, and the Mn molar ratio of the material is calculated.

[0239] The test method of the primary average particle size of the first lithium-containing transition metal phosphate material and the second lithium-containing transition metal phosphate material can be performed by methods and devices known in the art, for example, as follows: 0.05 g of the material to be tested is dissolved in 40 ml of anhydrous ethanol, then an appropriate amount of dispersant is added, and the mixture is stirred uniformly to obtain a suspension, 2 ml of the suspension and 2 ml of anhydrous ethanol are mixed, and then ultrasonic treatment is performed, the ultrasonic power is 480 W, and the ultrasonic time is 5 min, to obtain a uniformly dispersed suspension, an appropriate amount of the middle layer of the suspension is taken for transmission electron microscope (TEM) testing, the projection area of each primary particle in the TEM image is counted according to the definition of the primary particle, that is, the cross-sectional area S of the primary particle, the equivalent circle diameter of the primary particle is obtained by the equivalent circle method, that is, the primary particle size d of the primary particle, and in the above process of counting the primary particles and the primary particle sizes, the primary particles with a primary particle size less than 50 nm are not counted in the statistical range (that is, the primary particles with a primary particle size greater than or equal to 50 nm are effective particles). The cross-sectional areas S and the primary particle sizes d of at least 500 effective particles are tested, and the primary average particle size of the material to be tested = the total primary particle size of the primary particles / the total number of the primary particles.

[0240] In some embodiments, the Mn molar ratio of the first lithium-containing transition metal phosphate material is 0.4 to 0.9, which can be optionally 0.5 to 0.9.

[0241] In some embodiments, the Mn molar ratio of the second lithium-containing transition metal phosphate material is 0 to 0.6, which can be optionally 0 to 0.4, and more optionally 0.

[0242] In some embodiments, the Mn molar ratio of the second lithium-containing transition metal phosphate material is 0.02 to 0.6, which can be optionally 0.02 to 0.4, and more optionally 0.02.

[0243] In some embodiments, the Mn molar ratio of the second lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.4, more optionally 0.2.

[0244] In some embodiments, the weight percentage of the first lithium-containing transition metal phosphate material is 50%-95%, optionally 65%-90%, more optionally 70%-80%, and the weight percentage of the second lithium-containing transition metal phosphate material is 5%-50%, optionally 10%-35%, more optionally 20%-30%, based on the total weight of the lithium-containing transition metal phosphate material.

[0245] In some embodiments, the particle size distribution of primary particles with a primary particle size of 50-180 nm in the first lithium-containing transition metal phosphate material is less than or equal to 10%, optionally less than or equal to 8.5%, more optionally 1%-6%.

[0246] The number of primary particles with a primary particle size greater than or equal to 1200 nm in the 250 μm 2 The number of primary particles in the area is less than or equal to 15, optionally less than or equal to 12, more optionally 1-8.

[0247] The test method for the particle size distribution of primary particles with a primary particle size of 50-180 nm in the material can be performed by methods and devices known in the art, for example as follows: the primary particle size of each primary particle in the sample material is obtained by referring to the test method for the primary average particle size of the sample material, the number of primary particles with a primary particle size of 50-180 nm is denoted as M, and the total number of primary particles obtained by statistics (the number of primary particles with a primary particle size greater than or equal to 50 nm) is N, and the particle size distribution of primary particles with a primary particle size of 50-180 nm in the material is M / N*100%.

[0248] The number of primary particles with a primary particle size greater than or equal to 1200 nm in the 250 μm 2 The test method for the number of primary particles in the area can be performed by methods and devices known in the art, for example as follows: the electrode plate is prepared from the material to be tested and a polyvinylidene fluoride binder in a mass ratio of 95:5, the electrode plate is cut vertically to the large face of the electrode plate using an argon ion beam to expose the entire longitudinal section, the entire longitudinal section is photographed using a scanning electron microscope, and the projected area of each primary particle, i.e. the cross-sectional area S of the primary particle, is counted using Avizo 3D image processing software, and the equivalent circle diameter of the primary particle is obtained using the equivalent circle method, and the area of 250 μm 2The number of primary particles having a primary particle size of 1200 nm or more in the test region is counted, and 10 test regions are randomly selected in different regions of the longitudinal section of the pole piece for testing, and the average value is taken.

[0249] In some embodiments, the first lithium-containing transition metal phosphate material has a particle size distribution index of primary particles having a primary particle size of greater than 180 nm and less than 1200 nm of less than or equal to 0.45, which can be 0.36, and more preferably 0.20-0.30.

[0250] The particle size distribution index of primary particles having a primary particle size of greater than 180 nm and less than 1200 nm in the material can be determined by methods and equipment known in the art, for example as follows: the primary particle size of primary particles of the sample to be tested is determined by reference to the method for determining the average primary particle size of the sample material, and primary particles having a primary particle size of greater than 180 nm and less than 1200 nm are recorded as statistical particles,

[0251] The particle size distribution index PDI is the standard deviation σ of the particle size divided by the average particle size

[0252] wherein σ is the standard deviation of the particle size, x i is the primary particle size of each statistical primary particle, is the average primary particle size of the statistical particles, and n is the total number of statistical particles. The average primary particle size of the statistical particles is the total primary particle size of the statistical particles divided by the total number of statistical particles.

[0253] In some embodiments, the first lithium-containing transition metal phosphate material satisfies at least one of (a1)-(d1):

[0254] (a1) the (Dv90-Dv10) / Dv50 of the first lithium-containing transition metal phosphate material is 1-3;

[0255] (b1) the Dv50 of the first lithium-containing transition metal phosphate material is 0.35 μm-1.5 μm;

[0256] (c1) the Dv10 of the first lithium-containing transition metal phosphate material is 0.1 μm-0.4 μm;

[0257] (d1) the Dv90 of the first lithium-containing transition metal phosphate material is 2.5 μm-6 μm.

[0258] The volume distribution particle size Dv10, Dv50, Dv90 of the material are the meanings known in the art, which respectively represent the particle size corresponding to the cumulative volume distribution percentage of 10%, 50%, and 90% of the material, and can be determined by using instruments and methods known in the art. For example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method can be referred to for convenient determination by using a laser particle size analyzer. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0259] In some embodiments, the second lithium-containing transition metal phosphate material satisfies the following relationship: 1.5≤A / B≤10,

[0260] wherein A is the specific surface area of the second lithium-containing transition metal phosphate material; B% is the mass content of the third carbon coating layer in the second lithium-containing transition metal phosphate material.

[0261] The mass content of the carbon coating layer of the material can be determined by methods and devices known in the art, for example, as follows: after the material is burned using a high-frequency induction furnace, the carbon content is tested by infrared absorption method, and the specific testing process is based on the standard GB / T 20123-2006 / ISO 15350:2000.

[0262] The specific surface area of the material can be determined by methods and devices known in the art, for example, as follows: the specific surface area is tested by gas adsorption method, and the test is based on the test standard GB / T 19587-2017, which is as follows: the material is taken as a sample, the sample tube is immersed in liquid nitrogen at -196°C, the adsorption amount of nitrogen on the surface of the solid at different pressures is determined at 0.05-0.30 relative pressure, the monolayer adsorption amount of the sample is calculated based on the BET multilayer adsorption theory and its formula, and thus the specific surface area of the material is calculated.

[0263] In some embodiments, the specific surface area of the second lithium-containing transition metal phosphate material is 3m 2 / g-12m 2 / g.

[0264] In some embodiments, the mass content of the second carbon coating layer is 0.8%-2.0% based on the mass of the second lithium-containing transition metal phosphate material.

[0265] In some embodiments, the second lithium-containing transition metal phosphate material satisfies at least one of (a2)-(f2):

[0266] (a2) the Dv10 of the second lithium-containing transition metal phosphate material is 0.2μm-2μm;

[0267] (b2) the Dv50 of the second lithium-containing transition metal phosphate material is from 0.5 pm to 5 pm;

[0268] (c2) the Dv90 of the second lithium-containing transition metal phosphate material is from 1.5 pm to 10 pm;

[0269] (d2) the Dv99 of the second lithium-containing transition metal phosphate material is from 2 pm to 12 pm;

[0270] (e2) the powder compaction density of the second lithium-containing transition metal phosphate material under a pressure of 29400 N is from 2.25 g / cm3to 2.60 g / cm3. 3 3 ;

[0271] (f2) the powder electrical resistivity of the second lithium-containing transition metal phosphate material is from 0 W-cm to 59 W-cm.

[0272] In the present text, the term “Dv10” refers to the particle size corresponding to the 10% of the cumulative volume percentage of the particles in the particle size distribution.

[0273] In the present text, the term “Dv50” refers to the particle size corresponding to the 50% of the cumulative volume percentage of the particles in the particle size distribution.

[0274] In the present text, the term “Dv90” refers to the particle size corresponding to the 90% of the cumulative volume percentage of the particles in the particle size distribution.

[0275] In the present text, the term “Dv99” refers to the particle size corresponding to the 99% of the cumulative volume percentage of the particles in the particle size distribution.

[0276] The Dv10, Dv50, Dv90 and Dv99 of the material can be measured by methods and devices known in the art. For example, it can be determined by using a laser particle size analyzer (Malvern Master Size 3000) according to GB / T 19077.1-2016.

[0277] ​The powder compaction density of the material can be measured by using a compaction density instrument according to GB / T 24533-2009. Specifically, a certain amount of material powder is placed on a compaction special mold (the diameter of the mold is known), and each of the upper and lower hollows in the middle of the mold has a metal disc. The powder is placed between the metal discs, a metal cylinder is placed on top, the mold is placed on the compaction density instrument, the pressure is set to 29400N, and the thickness of the powder under the pressure of 29400N can be read on the device. The powder compaction density of the material is p = m / v, where v = (S x 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 model of the compaction density instrument is UTM7305, and the manufacturer is Sansi Zongheng.

[0278] The powder resistivity of the material can be measured by using a method and device known in the art. For example, the powder resistivity can be measured by using a powder resistivity instrument (Suzhou Jingge, model ST2722) according to GB / T 33822-2017. Specifically, a certain amount of material (for example, 1g) is weighed and added to the charging cavity of the powder resistivity instrument, an 8MPa pressure is applied, and the forward resistivity and reverse resistivity of the material are measured respectively. The average of the two is taken as the powder resistivity of the material.

[0279] In some embodiments, the method for preparing the positive electrode active material comprises:

[0280] mixing the first lithium-containing transition metal phosphate material, the second lithium-containing transition metal phosphate material, and the third lithium-containing transition metal phosphate material to obtain a lithium-containing transition metal phosphate material,

[0281] The first lithium-containing transition metal phosphate material comprises a first inner core and a first carbon coating layer coated on the outer surface of the first inner core, and the second lithium-containing transition metal phosphate material comprises a second inner core and a second carbon coating layer coated on the outer surface of the second inner core,

[0282] The primary average particle size of the first lithium-containing transition metal phosphate material is smaller than the primary average particle size of the second lithium-containing transition metal phosphate material,

[0283] The Mn molar percentage of the second lithium-containing transition metal phosphate material is smaller than the Mn molar percentage of the first lithium-containing transition metal phosphate material,

[0284] The primary average particle size of the first lithium-containing transition metal phosphate material is 120nm-600nm,

[0285] The primary average particle size of the second lithium-containing transition metal phosphate material is 250nm-4000nm,

[0286] The third lithium-containing transition metal phosphate material comprises a third inner core and a third carbon coating layer coated on the outer surface of the third inner core,

[0287] The primary average particle size of the third lithium-containing transition metal phosphate material is less than the primary average particle size of the first lithium-containing transition metal phosphate material,

[0288] The Mn molar ratio of the third lithium-containing transition metal phosphate material is less than the Mn molar ratio of the first lithium-containing transition metal phosphate material,

[0289] The primary average particle size of the third lithium-containing transition metal phosphate material is 50 nm-200 nm.

[0290] In some embodiments, the Mn molar ratio of the third lithium-containing transition metal phosphate material is 0-0.6, optionally 0-0.4, optionally 0-0.2, and more optionally 0.

[0291] In some embodiments, the Mn molar ratio of the third lithium-containing transition metal phosphate material is 0.02-0.6, optionally 0.02-0.4, optionally 0.02-0.2, and more optionally 0.02.

[0292] In some embodiments, the average value of the Mn molar ratio of the third lithium-containing transition metal phosphate material is 0.2-0.6, optionally 0.2-0.4, and more optionally 0.2.

[0293] In some embodiments, the weight percentage of the first lithium-containing transition metal phosphate material is 60%-90%, optionally 65%-80%, and more optionally 70%-80%, the weight percentage of the second lithium-containing transition metal phosphate material is 5%-30%, optionally 10%-30%, and more optionally 20%-30%, and the weight percentage of the third lithium-containing transition metal phosphate material is 1%-10%, optionally 2%-8%, and more optionally 3%-7%, based on the total weight of the lithium-containing transition metal phosphate material.

[0294] In some embodiments, the composition general formula of the first inner core comprises Li m4 A4 a4 Fe x4 Mn y4 M4 b4 P z4 Q4 c4 O n4 N4 d4 ,

[0295] 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,

[0296] The general formula of the second inner core comprises 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,

[0297] The general formula of the third inner core comprises Li m6 A6 a6 Fe x6 Mn y6 M6 b6 P z6 Q6 c6 O n6 N6 d6 ,

[0298] 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,

[0299] A4, A5, A6 each independently comprises one or more of Al, Na, K, Mg, M4, M5, M6 each independently comprises one or more of Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, Q4, Q5, Q6 each independently comprises one or more of B, S, Si, N, N4, N5, N6 each independently comprises one or more of S, F, Cl, Br.

[0300] [positive electrode tab]

[0301] The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material.

[0302] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two opposite surfaces of the positive electrode current collector.

[0303] In some embodiments, the positive electrode film layer further comprises a binder and a conductive agent.

[0304] In some embodiments, 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).

[0305] In some embodiments, the single-side area density of the positive electrode film layer is 300 mg / 1540 mm 2 -580 mg / 1540 mm 2 .

[0306] The single-side area density of the positive electrode film layer can be tested by a method known in the art. For example, place the battery in a 25℃ oven environment, stand for 2h, and when the battery temperature is maintained at 25℃, discharge the battery at 1 / 3C constant current to 2.0V, disassemble the battery, obtain the positive electrode sheet, treat the residual electrolyte with dimethyl carbonate solvent, dry the sheet, cut into small round pieces with an area of 1540 mm 2 , weigh M, then wipe off the positive electrode film layer of the above weighed sheet, weigh the current collector, and record as N, then the single-side coating weight is (M-N) / 2.

[0307] In some embodiments, the single-side area density of the positive electrode film layer is 300 mg / 1540 mm 2 , 340 mg / 1540 mm 2 , 380 mg / 1540 mm 2 , 420 mg / 1540 mm 2 , 460 mg / 1540 mm 2 , 500 mg / 1540 mm 2 , 540 mg / 1540 mm 2 , 580 mg / 1540 mm 2 , or a range between any two of the above values.

[0308] In some embodiments, the compaction density of the positive electrode film layer is 2.25 g / cm 3 -2.75 g / cm 3 .

[0309] The compaction density of the positive electrode film layer 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 h, until the battery temperature is maintained at 25 °C, the battery is discharged at 1 / 3 C constant current to 2.0 V, the battery is disassembled, the positive electrode sheet is obtained, residual electrolyte is treated with dimethyl carbonate solvent, the sheet is dried, cut into a small disc with an area of S, weighed as W1, and the thickness T1 of the positive electrode sheet is measured using a micrometer, then the positive electrode film layer of the above weighed sheet is wiped off, the weight of the current collector is weighed as W2, and the thickness T2 of the current collector is measured using a micrometer, then the compaction density PD of the positive electrode film layer is (W1-W2) / [(T1-T2) x S].

[0310] In some embodiments, the compaction density of the positive electrode film layer is 2.25 g / cm 3 , 2.35 g / cm 3 , 2.45 g / cm 3 , 2.55 g / cm 3 , 2.65 g / cm 3 , 2.75 g / cm 3 , or any value therebetween.

[0311] The compaction density of the positive electrode film layer is within a suitable range, and the battery has excellent volumetric energy density and rate performance.

[0312] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0313] In some embodiments, the positive electrode film layer can further optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0314] In some embodiments, the positive electrode film layer can further optionally include a conductive agent. As an example, the conductive agent can include at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0315] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode current collector to drying, cold pressing, and the like to obtain the positive electrode sheet.

[0316] [Positive electrode sheet]

[0317] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0318] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two surfaces of the negative electrode current collector.

[0319] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. As the metal foil, for example, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer (e.g., a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0320] In some embodiments, the negative electrode active material can be a negative electrode active material known in the art for use in a battery. As an example, the negative electrode active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material can be selected from at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be selected from at least one of elemental tin, a tin oxide compound, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0321] In some embodiments, the negative electrode film layer can also optionally include a binder. The binder can 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).

[0322] In some embodiments, the negative electrode film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0323] In some embodiments, the negative electrode film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

[0324] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative electrode current collector, and after processes such as drying, cold pressing, and the like, the negative electrode sheet can be obtained.

[0325] [Electrolyte]

[0326] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0327] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0328] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorodioxalate phosphate.

[0329] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, and the like.

[0330] [Separator]

[0331] The separator of the present application employs the above-mentioned separator. In addition, the separator of the present application can be used in combination with other commonly used separators in the art, as needed.

[0332] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a roll process or a stacking process.

[0333] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte.

[0334] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0335] [Secondary battery]

[0336] In one embodiment of the present application, a secondary battery is provided, which includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, and the binder in the active material layer of the positive electrode sheet includes the polymer of any embodiment of the present application.

[0337] In some embodiments, the secondary battery is a lithium ion battery or a sodium ion battery. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0338] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0339] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte described above.

[0340] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0341] The shape of the secondary battery is not particularly limited in the present application, and it can be cylindrical, square, or any other shape. For example, FIG. 3 is a secondary battery 5 of a square structure as an example.

[0342] In some embodiments, referring to FIG. 4, the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate form an accommodation cavity. The shell 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can be arranged on the opening to close the accommodation cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be made into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the accommodation cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the skilled person can select according to the specific actual needs.

[0343] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0344] FIG. 5 is a battery module 4 as an example. Referring to FIG. 5, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0345] Optionally, the battery module 4 can also include a housing having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.

[0346] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0347] FIGS. 6 and 7 are a battery pack 1 as an example. Referring to FIGS. 6 and 7, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0348] In addition, the present application also provides a power utilization device, which includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0349] As the power utilization device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirements thereof.

[0350] FIG. 8 is a power utilization device as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power utilization device, a battery pack or a battery module can be used.

[0351] As another example, the device can be a mobile phone, a tablet, a notebook computer, etc. The device generally requires thinness, and a secondary battery can be used as a power source.

[0352] Embodiments

[0353] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application only and are not to be understood as limiting the present application. In the embodiments, specific techniques or conditions not described are performed in accordance with techniques or conditions described in the literature in the field or in accordance with product manuals. Reagents or instruments not described by the manufacturer are all conventional products that can be obtained commercially.

[0354] Table 1: Performance parameters and grades of first lithium-containing transition metal phosphate material

[0355] Table 2: Performance parameters and grades of second lithium-containing transition metal phosphate material

[0356] Table 3: Performance parameters and grades of third lithium-containing transition metal phosphate material

[0357] I. Preparation method

[0358] Embodiment 1

[0359] (1) Preparation of positive electrode sheet:

[0360] The first lithium-containing transition metal phosphate material A1 and the second lithium-containing transition metal phosphate material B1 were mixed at a mass ratio of 70:30 to obtain a positive electrode active material. The mixed positive electrode active material, the conductive agent conductive carbon black, and the binder polyvinylidene fluoride were mixed at a weight percentage of 96:1.5:2.5, and N-methylpyrrolidone was added. After sufficient mixing, stirring, and dispersion, a positive electrode slurry was prepared.

[0361] The viscosity of the slurry after mixing and stirring was adjusted to 8000-20000 mPa.s until the slurry was not stratified. The slurry was coated on the surface of the substrate aluminum foil at a thickness of 420 mg / 1540 mm 2 through a double-sided double-control coating device, and then dried, cold-pressed, cut, and sheeted to obtain a positive electrode sheet.

[0362] (2) Preparation of negative electrode sheet:

[0363] The artificial graphite, conductive agent conductive carbon black, binder styrene-butadiene rubber (SBR) and thickening agent sodium carboxymethyl cellulose (CMC) are mixed uniformly according to the weight percentage of 95:1.0:2.0:2.0 and deionized water is added. After stirring and dispersing, a negative electrode slurry is obtained. The negative electrode slurry is coated on a copper foil substrate, dried, cold-pressed, cut, and sheeted to obtain a negative electrode sheet. 2 The negative electrode sheet is coated on the substrate copper foil, dried, cold-pressed, cut, and sheeted to obtain a negative electrode sheet.

[0364] (3) Separator

[0365] A polypropylene film is used as the separator film.

[0366] (4) Electrolyte

[0367] In an argon atmosphere glove box (H2O <0.1 ppm, O2 <0.1 ppm), organic solvents ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) are mixed uniformly according to the volume ratio of 1:1:1:1. LiPF6 is dissolved in the organic solvent and stirred uniformly to obtain an electrolyte with a concentration of 1 mol / L, thereby obtaining the electrolyte of Example 1.

[0368] (5) Preparation of the battery:

[0369] The positive electrode sheet, the separator film, and the negative electrode sheet are stacked in order, and the separator film can function to separate the cathode and the anode. A bare cell is obtained by winding, and the bare cell is placed in an outer package, injected with electrolyte, and subjected to processes such as packaging, formation, and degassing, thereby obtaining a lithium ion battery.

[0370] Examples 2-13 and Comparative Examples 1-2 are prepared in a manner similar to that of 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:

[0371] Table 4

[0372] II. Test Methods

[0373] 1. Fast charging performance test of the battery

[0374] At 40°C, the battery is charged at 4C constant current to a charge cut-off voltage of 4.1V, then charged at constant voltage until the current is 0.05C, left for 5 min, then discharged at 0.33C constant current to a discharge cut-off voltage of 2.0V, and the actual capacity is recorded as C0.

[0375] Then the battery is sequentially charged at 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, 4.5C0 constant current to full battery charging cut-off voltage 4.1V or 0V negative electrode cut-off potential (whichever is reached first), after each charging is completed, it needs to be discharged at 1C0 to full battery discharge cut-off voltage 2.0V, record the negative electrode potential corresponding to 10%, 20%, 30%…80% SOC (State of Charge) when charging at different charging rate, draw the rate-negative electrode potential curve at different SOC state, linear fitting to obtain the charging rate corresponding to the negative electrode potential of 0V at different SOC state, which is the charging window at this SOC state, respectively recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, according to the formula (60 / C20% SOC+60 / C30% SOC+60 / C40% SOC+60 / C50% SOC+60 / C60% SOC+60 / C70% SOC+60 / C80% SOC) x 10% to calculate the charging time T of the battery from 10% SOC to 80% SOC. The shorter the charging time T, the better the fast charging performance of the secondary battery.

[0376] 2. Storage performance of the battery

[0377] The battery is placed in a 40℃ oven environment and left for 2h, and the battery temperature is 40℃; then the battery is discharged at 1 / 3C constant current to 2.0V; after 5min, the battery is charged at 1 / 3C constant current to voltage 4.1V, then charged at 4.1V constant voltage until the current is 0.05C, and left for 5min, then the battery is discharged at 1 / 3C constant current to voltage 2.0V, which is one charging and discharging process, and the discharge capacity C1 of the first cycle is recorded, and then the fully charged battery is placed in a 60℃ environment, and the remaining capacity is tested at 40℃ at regular intervals until the discharge capacity of the secondary battery decays to 80%, and the storage time is recorded.

[0378] 3. Volume energy density of the battery

[0379] Capacity test of the battery monomer: the battery monomer is placed at 40℃ for 2h to ensure that the temperature of the battery monomer is 40℃, then the battery is discharged at 1 / 3C constant current to 2.0V; after 5min, the battery monomer is charged at 1 / 3C constant current to 4.1V, and continues to be charged at 4.1V constant voltage until the current is 0.05C, and left for 5min, then the battery monomer is discharged at 1 / 3 constant current to 2.0V, and the total discharge capacity C0 of the battery monomer is recorded, and the total discharge energy E0 is Wh.

[0380] Battery cell volume measurement: measure the length, width, height of the battery outer surface using a caliper, calculate the cell volume V0, unit L.

[0381] Volume energy density calculation: the battery cell discharge energy E0 / battery volume V0 is the volume energy density of the battery cell.

[0382] III. Analysis of test results of each embodiment and comparative example

[0383] According to the above method, the secondary batteries of each embodiment and comparative example were prepared, and each parameter was measured, and the results are shown in the following table.

[0384] Table 5

[0385] The positive electrode film layer in embodiments 1-13 of the present application comprises first particles and second particles, wherein the primary particle size of the first particles is greater than 180 nm and less than 900 nm, the primary particle size of the second particles is greater than or equal to 900 nm and less than or equal to 5 μm, and the average value of the Mn molar fraction of the second particles is less than the average value of the Mn molar fraction of the first particles.

[0386] From the comparison of embodiments 1-13 and comparative examples 1-2, it can be seen that by controlling the average value of the Mn molar fraction of the second particles to be less than the average value of the Mn molar fraction of the first particles, the present application can balance high powder compaction density and specific capacity, shorten the charging time of the battery, and improve the energy density and rate performance of the battery.

[0387] Table 6

[0388] From embodiments 1-10, it can be seen that based on the total number of moles of Mn in the primary particles of the positive electrode film layer, the mole percentage of Mn in the second particles is 0%-50%, the battery has a shorter charging time, and the battery has excellent rate performance, high energy density, and long storage life. From the comparison of embodiment 4 and embodiment 7, it can be seen that by controlling the mole percentage of Mn in the second particles to be 0%-10%, the charging time of the battery can be shortened, and the rate performance of the battery can be improved. From the comparison of embodiment 6 and embodiment 2, it can be seen that by controlling the mole percentage of Mn in the second particles to be 0%-10%, the charging time of the battery can be shortened, and the rate performance of the battery can be improved.

[0389] From the comparison of embodiment 7 and embodiment 4, it can be seen that the mole percentage of Mn in the second particles is 5%-50%, which can improve the storage life of the battery and improve the storage life of the battery. From the comparison of embodiment 2 and embodiment 6, it can be seen that by controlling the mole percentage of Mn in the second particles to be 10%-50%, the storage life of the battery can be improved, and the storage life of the battery can be improved.

[0390] From the comparison of Example 6 and Example 2, it can be seen that the ratio of the average value of the Mn molar ratio of the second type of particles to the average value of the Mn molar ratio of the first type of particles is 0-0.5, which can further shorten the charging time of the battery and improve the rate performance of the battery.

[0391] From Examples 3, 9, and 10, it can be seen that controlling the average value of the Mn molar ratio of the first type of particles to be 0.4-0.9 can balance the storage life, charging time, and energy density of the battery. From the comparison of Examples 3, 9, and Example 10, it can be seen that controlling the average value of the Mn molar ratio of the first type of particles to be 0.5-0.9 can further improve the energy density of the battery.

[0392] From Examples 1-4, it can be seen that controlling the average value of the Mn molar ratio of the second type of particles to be 0-0.6 can balance the storage life, charging time, and energy density of the battery. From the comparison of Examples 1, 4, and Examples 2-3, it can be seen that controlling the average value of the Mn molar ratio of the second type of particles to be 0-0.1 can further shorten the charging time of the battery, improve the rate performance of the battery, and prolong the cycle life of the battery.

[0393] From the comparison of Examples 3-4 and Examples 1, 2, it can be seen that controlling the average value of the Mn molar ratio of the second type of particles to be 0.1-0.3 can further improve the energy density of the battery. From the comparison of Example 4 and Example 3, it can be seen that controlling the average value of the Mn molar ratio of the second type of particles to be 0.1 can further prolong the storage life of the battery on the premise of high energy density.

[0394] From Examples 3, 5-8, it can be seen that controlling the area ratio of the first type of particles to be 20%-95% and the area ratio of the second type of particles to be 5%-80% can balance the rate performance, storage performance, and energy density of the battery. From the comparison of Examples 3, 7-8 and Examples 5-6, it can be seen that controlling the area ratio of the first type of particles to be 20%-80% and the area ratio of the second type of particles to be 15%-80% can shorten the charging time of the battery, prolong the storage life of the battery, and balance the high energy density of the battery. From the comparison of Example 8 and Examples 3, 5-7, it can be seen that controlling the area ratio of the first type of particles to be 40%-60% and the area ratio of the second type of particles to be 25%-60% can further shorten the charging time of the battery, improve the rate performance of the battery, and balance the high energy density and long storage life of the battery.

[0395] Table 7

[0396] From the comparison of the embodiments 11-12 and the embodiment 1, it can be seen that the positive electrode film layer further comprises the third type of particles with a primary particle size of 50-180 nm, and the area ratio of the third type of particles is greater than or equal to 5% and less than or equal to 30%, which can further improve the powder compaction density of the active material and improve the energy density of the battery.

[0397] From the embodiments 11-13, it can be seen that the control of the Mn molar percentage in the third type of particles is 0-12%, the battery has a shorter charging time, and the battery has excellent rate performance, high energy density and long storage life.

[0398] From the comparison of the embodiments 11-12 and the embodiment 13, it can be seen that the control of the Mn molar percentage of the third type of particles is 0.02-0.2, which can improve the gram capacity of the material, improve the energy density of the battery, shorten the charging time of the battery, and improve the rate performance of the battery. From the comparison of the embodiment 11 and the embodiments 12-13, it can be seen that the control of the Mn molar percentage of the third type of particles is 0.02, which can improve the gram capacity of the material, prolong the storage time of the battery, improve the storage life of the battery, shorten the charging time of the battery, and improve the rate performance of the battery.

[0399] From the comparison of the embodiment 12 and the embodiments 11 and 13, it can be seen that the control of the Mn molar percentage of the third type of particles is 0.1-0.2, which can further improve the energy density of the battery.

[0400] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the components of the embodiments are also included in the scope of the present application.

Claims

A secondary battery characterized by The positive electrode film layer comprises a first type of particles and a second type of particles, the first type of particles and the second type of particles comprise a lithium-containing transition metal phosphate material, The first type of particles has a primary particle size greater than 180 nm and less than 900 nm, and the second type of particles has a primary particle size greater than or equal to 900 nm and less than or equal to 5 microns, The average value of the Mn molar fraction of the second type of particles is less than the average value of the Mn molar fraction of the first type of particles, The Mn molar fraction refers to the proportion of the number of moles of Mn to the total number of moles of Mn and Fe. The percentage of Mn in the second type of particles is 0-50%, optionally 0-30%, more optionally 0-10%, and further optionally 0%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer. The percentage of Mn in the second type of particles is 5-50%, optionally 5-30%, more optionally 5-10%, and further optionally 5%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer. The secondary battery according to claim 1, characterized in that, The percentage of Mn in the second type of particles is 10-50%, optionally 10-30%, and more optionally 10%, based on the total number of moles of Mn in the primary particles of the positive electrode film layer. The secondary battery according to claim 1, characterized in that, The ratio of the average value of the Mn molar fraction of the second type of particles to the average value of the Mn molar fraction of the first type of particles is 0-0.8, optionally 0-0.5, and more optionally 0. The secondary battery according to claim 1, characterized in that The ratio of the average value of the Mn molar fraction of the second type of particles to the average value of the Mn molar fraction of the first type of particles is 0.0003-0.8, optionally 0.0003-0.5, and more optionally 0.0003. The secondary battery according to any one of claims 1 to 4, characterized in that, The ratio of the average value of the Mn molar fraction of the second type of particles to the average value of the Mn molar fraction of the first type of particles is 0.002-0.8, optionally 0.002-0.5, and more optionally 0.

002. The secondary battery according to any one of claims 1 to 4, characterized in that, The average value of the Mn molar fraction of the first type of particles is 0.4-0.9, optionally 0.5-0.

9. The secondary battery according to any one of claims 1 to 4, characterized in that, The average value of the Mn molar fraction of the second type of particles is 0-0.6, optionally 0-0.5, more optionally 0-0.1, and further optionally 0. The secondary battery according to any one of claims 1 to 7, characterized in that, The average value of the Mn molar fraction of the second type of particles is 0.02-0.6, optionally 0.02-0.2, and more optionally 0.

02. The secondary battery according to any one of claims 1 to 8, characterized in that, The average value of the Mn molar fraction of the second type of particles is 0.1-0.3, optionally 0.

1. The secondary battery according to any one of claims 1 to 8, characterized in that, The area percentage of the first type of particles is 20-95%, optionally 20-80%, and more optionally 40-60%, and / or the area percentage of the second type of particles is 5-80%, optionally 15-80%, and more optionally 25-60%, based on the total area of the primary particles of the positive electrode film layer. The secondary battery according to any one of claims 1 to 8, characterized in that, ​ The secondary battery according to any one of claims 1 to 11, characterized in that, ​ ​ The secondary battery according to any one of claims 1 to 11, characterized in that, The positive electrode film layer comprises third type particles, the third type particles comprise the lithium-containing transition metal phosphate material, and a primary particle size of the third type particles is 50 nm-180 nm, The area percentage of the third type particles is greater than or equal to 5% and less than or equal to 30% based on the total area of the primary particles of the positive electrode film layer. The secondary battery according to claim 13, characterized by The average value of the Mn molar percentage of the third type particles is less than the average value of the Mn molar percentage of the first type particles. The secondary battery according to claim 13 or 14, characterized in that The percentage of Mn in the third type particles is 0%-12% based on the total number of moles of Mn in the primary particles of the positive electrode film layer, which is optionally 0%-8%, more optionally 0%-6%, and further optionally 0%. The secondary battery according to claim 13 or 14, characterized in that The percentage of Mn in the third type particles is 0.02%-12% based on the total number of moles of Mn in the primary particles of the positive electrode film layer, which is optionally 0.02%-8%, more optionally 0.02%-6%, and further optionally 0.02%. The secondary battery according to claim 13 or 14, characterized in that The percentage of Mn in the third type particles is 0.2%-12% based on the total number of moles of Mn in the primary particles of the positive electrode film layer, which is optionally 0.2%-8%, more optionally 0.2%-6%, and further optionally 0.2%. The secondary battery according to any one of claims 13-17, characterized In the present application, The ratio of the average value of the Mn molar percentage of the third type particles to the average value of the Mn molar percentage of the first type particles is 0-0.8, which is optionally 0-0.4, and more optionally 0. The secondary battery according to any one of claims 13 to 17, characterized in that, The ratio of the average value of the Mn molar percentage of the third type particles to the average value of the Mn molar percentage of the first type particles is 0.0003-0.8, which is optionally 0.0003-0.4, and more optionally 0.0003. The secondary battery according to any one of claims 13 to 17, characterized in that, The ratio of the average value of the Mn molar percentage of the third type particles to the average value of the Mn molar percentage of the first type particles is 0.002-0.8, which is optionally 0.002-0.4, and more optionally 0.

002. The secondary battery according to any one of claims 13 to 20, characterized in that, The average value of the Mn molar percentage of the third type particles is 0-0.6, which is optionally 0-0.4, more optionally 0-0.2, and further optionally 0. The secondary battery according to any one of claims 13 to 20, characterized in that, The average value of the Mn molar percentage of the third type particles is 0.02-0.6, which is optionally 0.02-0.4, more optionally 0.02-0.2, and further optionally 0.

02. The secondary battery according to any one of claims 13 to 20, characterized in that, The average value of the Mn molar percentage of the third type particles is 0.1-0.2, which is optionally 0.

1. The secondary battery according to any one of claims 13 to 23, characterized in that, The area percentage of the first type particles is 45%-85%, the area percentage of the second type particles is 10%-40%, and the area percentage of the third type particles is 5%-15% based on the total area of the primary particles of the positive electrode film layer. The secondary battery according to any one of claims 1 to 24, characterized in that, The average value of the Mn molar percentage of the primary particles of the positive electrode film layer is 0.2-0.9, which is optionally 0.4-0.

8. The secondary battery according to any one of claims 1 to 25, characterized in that, The particle size distribution index of the primary particle size of the first 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 first type particles to the average primary particle size of the first type particles. The secondary battery according to any one of claims 13 to 26, characterized in that, The composition general formula of the lithium-containing transition metal phosphate material of the first 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, The composition general formula of the lithium-containing transition metal phosphate material of the second 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, 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. The secondary battery according to any one of claims 1 to 27, characterized in at least one lithium-containing transition metal phosphate material, wherein the positive electrode active material has a powder compaction density of 2.40 g / cm3or greater at a pressure of 29400 N 3 -2.65 g / cm3 3 . The secondary battery according to claim 28, characterized by The gram capacity of the positive electrode active material at 40 DEG C and 1 / 3 C discharge rate is 135 mAh / g-150 mAh / g. 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). The secondary battery according to any one of claims 1 to 30, characterized in that, The single-sided areal density of the positive electrode film layer is 300 mg / 1540 mm 2 - 580 mg / 1540 mm 2 . The secondary battery according to any one of claims 1 to 31, characterized in that, The compacted density of the positive electrode film layer is 2.25 g / cm 3 - 2.75 g / cm 3 . An electric power utilization device characterized by comprising: The power-using device comprises the secondary battery according to any one of claims 1 to 32.

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