Positive electrode sheet, secondary battery, and electric device

Abstract

This application discloses a positive electrode sheet, a secondary battery, and an electrical device. Among them, the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes Li (Mn) , 2 , 1‑z , z Ni b Co c M 1d M 2e O f R′ g , where 0.75 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, and M1 is Mn element and / or Al element; the second positive electrode active material includes Li 1+x M 3n Mn 1‑y A′ y P 1‑z E z O4, where -0.100 ≤ x ≤ 0.100, 0 ≤ n ≤ 1.1, 0.001 ≤ y ≤ 0.500, 0 ≤ z ≤ 0.100, and A′ includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge; the positive electrode sheet satisfies: where: 0.1 ≤ R ≤ 1.2; w (Mn) is the mass fraction of Mn in the positive electrode active material layer; d is the thickness of the positive electrode active material layer, with the unit of mm; T is the weight of the positive electrode active material layer per unit area of the positive electrode sheet, with the unit of g / cm 2 ; R is the resistance of the positive electrode sheet at 25°C, with the unit of Ω.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and more specifically, relates to a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0002] Lithium-ion batteries have the characteristics of being green, environmentally friendly, high-energy, and low-carbon. They are not only used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, but also widely used in electric transportation such as electric bicycles, electric motorcycles, and electric vehicles, as well as in multiple fields such as military equipment and aerospace. With the development of society, people's requirements for lithium-ion batteries are getting higher and higher, and fast charging performance and long service life have become important performance indicators for lithium batteries. Currently, the positive electrode materials of lithium-ion batteries mostly use ternary layered positive electrode materials, such as nickel cobalt manganese (NCM) system materials. However, conventional NCM system materials have a poor rate tolerance boundary at low voltages, which will affect the fast charging ability and actual available capacity of the battery. Summary of the Invention

[0003] In view of the technical problems in the background art, this application provides a positive electrode sheet, aiming to broaden the rate tolerance boundary of the positive electrode active material at high and low voltages, improve the fast charging ability, and at the same time obtain a long service life.

[0004] To achieve the above object, a first aspect of this application provides a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material.

[0005] The first positive electrode active material includes Li ,

[0004] ,

[0005] , 1+x , f ,

[0003] , 1d , 1-z , b , 1-y ,

[0006] , , 3n , , g , 2e , c , a , z , y Ni b Co c M 1d M 2e O f R′ g where 0.75 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is Mn element and / or Al element, M2 includes one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb; R′ includes one or more elements of N, F, S, Cl;

[0006] The second positive electrode active material includes Li 1+x M 3n Mn 1-y A′ y P 1-z E zO4, wherein -0.100≤x≤0.100, 0≤n≤1.1, 0.001≤y≤0.500, 0≤z≤0.100, M3 includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, A′ includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb and Ge, and E includes one or more elements selected from B, Si, N, S, F, Cl and Br;

[0007] The positive electrode plate satisfies:

[0008]

[0009] Where: 0.1≤R≤1.2;

[0010] w (Mn) The mass fraction of Mn in the positive electrode active material layer;

[0011] d represents the thickness of the positive electrode active material layer, in mm;

[0012] T represents the weight of the positive electrode active material layer per unit area of ​​the positive electrode sheet, in g / cm³. 2 ;

[0013] R is the resistance of the positive electrode at 25°C, in Ω.

[0014] Compared with the prior art, the positive electrode of the first aspect of this application has at least the following beneficial effects: (1) Li a Ni b Co c M 1d M 2e O f R′ g The positive electrode active material system exhibits poor rate tolerance at low SOC (state of charge, i.e., remaining charge), while Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 has a poor rate tolerance boundary at high SOC. By combining the two, the defects of both systems can be compensated at the same time, and the rate tolerance boundary at high and low SOC can be widened, thereby improving the fast charging capability; (2) By using the positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ g With positive electrode active material Li 1+x M3n Mn 1-y A′ y P 1-z E z O4 mixing can further enable the battery to have both high energy density and good cycle performance, and extend its service life; (3) Although the mechanism is not yet clear, by controlling the content of Mn element in the positive electrode active material layer, the thickness and areal density of the positive electrode active material layer and the resistance of the positive electrode sheet to meet the above formula range, fast charging capability, energy density and cycle performance can be guaranteed at the same time, and a fast charging positive electrode sheet with good cycle life can be obtained.

[0015] In some embodiments of this application, Optionally, Among them, w (A′) w represents the mass fraction of A′ in the positive electrode active material layer. (P) This refers to the mass fraction of P in the positive electrode active material layer. By... By keeping it within the given range, both fast charging performance and long service life can be further balanced.

[0016] In some embodiments of this application, 0.01 ≤ w (A′) ≤0.05.

[0017] In some embodiments of this application, the second positive electrode active material includes at least one of the following two positive electrode active materials: (i) 0.001≤y≤0.500, n=0, and the second positive electrode active material is Li. 1+x Mn 1-y A′ y P 1-z E z O4; (ii) 0.001≤y≤0.500, 0.9≤n≤1.1, the second positive electrode active material is Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4; optionally, the second positive electrode active material is: (ii) Li 1+x Mn 1-y A′ y P 1-z E z O4.

[0018] In some embodiments of this application, 0.032 ≤ T ≤ 0.043, and optionally, 0.035 ≤ T ≤ 0.039. By controlling T within the given range, improved fast-charging performance and cycle life, as well as higher energy density, can be further obtained.

[0019] In some embodiments of this application, 0.11 ≤ d ≤ 0.16, and optionally, 0.12 ≤ d ≤ 0.14. By controlling d within the given range, improved fast-charging performance and cycle life, as well as higher energy density, can be further obtained.

[0020] In some embodiments of this application, 0.1 ≤ R ≤ 1. By controlling R within the given range, the internal resistance of the electrode can be further reduced, thereby improving fast charging performance and cycle performance.

[0021] In some embodiments of this application, M1 is an element of Mn.

[0022] In some embodiments of this application, Optionally, Alternatively, 5 By controlling Within the given range, it is possible to improve fast charging capabilities while also maintaining higher energy density and better cycle performance, thereby extending service life.

[0023] In some embodiments of this application, the Dv50 particle size of the second positive electrode active material is 0.21 μm to 1.53 μm, optionally 0.32 μm to 1.4 μm, optionally 0.41 μm to 1.25 μm, optionally 0.38 μm to 1.1 μm, and optionally 0.47 μm to 0.91 μm.

[0024] In some embodiments of this application, the specific surface area of ​​the second positive electrode active material is 9.2 m². 2 / g~23.6m 2 / g, optional 10.5m 2 / g~19.6m 2 / g, or 12.0m 2 / g~16.2m 2 / g, or alternatively 10.0m 2 / g~21.5m 2 / g, or 10.9m. 2 / g~17.6m 2 / g.

[0025] In some embodiments of this application, Optionally, By controlling the positive electrode to meet the given conditions, the composite positive electrode can be further made to have better power capability and better cycle life.

[0026] In some embodiments of this application, the Dv50 particle size of the first positive electrode active material is 2.1 μm to 6.3 μm, and can be optionally 3.5 μm to 4.9 μm.

[0027] In some embodiments of this application, the specific surface area of ​​the first positive electrode active material is 0.3 m². 2 / g~1.2m 2 / g, optional 0.5m 2 / g~0.9m 2 / g.

[0028] In some embodiments of this application, the surface of the first positive electrode active material is provided with a first coating layer. Optionally, the first coating layer includes one or more elements selected from Ti, Al, B, Nb, Zr, Si, and W.

[0029] In some embodiments of this application, the thickness of the first coating layer is 20 nm to 150 nm.

[0030] In some embodiments of this application, the surface of the second positive electrode active material is provided with a second coating layer. Optionally, the second coating layer includes at least one of pyrophosphate, phosphate, and carbon.

[0031] In some embodiments of this application, the thickness of the second coating layer is 10 nm to 50 nm.

[0032] In some embodiments of this application, E in the second positive electrode active material includes one or more elements selected from B, Si, N, and S.

[0033] In some embodiments of this application, A′ in the second positive electrode active material includes one or more elements selected from Fe, Ti, V, Ni, Co, and Mg.

[0034] A second aspect of this application provides a secondary battery comprising: a positive electrode sheet according to the first aspect of this application.

[0035] A third aspect of this application provides an electrical device comprising: a positive electrode plate of the first aspect of this application, and / or a secondary battery as described in the second aspect of this application. Detailed Implementation

[0036] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0037] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0038] The "range" disclosed in this application is defined in the form of a lower limit and / or an upper limit. A given range is defined by selecting a lower limit and / or an upper limit, which defines the boundary of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined range, and any lower limit can be combined with other lower limits to form an undefined range. Similarly, any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value, or with other lower or upper limits, to form an undefined range. For example, if a range of no more than 150 is listed for a specific parameter, it is expected that ranges such as 10–140 and 20–120 satisfying the condition of no more than 150 are also considered acceptable. Furthermore, if the minimum range values ​​listed are 2.1 and 3.5, and if the maximum range values ​​are 4.9 and 6.3, then the following ranges can all be expected: 2.1–6.3, 2.1–4.9, 3.5–6.3, and 3.5–4.9. In this application, unless otherwise stated, numerical ranges such as “10–50” represent abbreviated representations of any combination of real numbers between 10 and 50, where 10 and 50 are real numbers. For example, the numerical range “20–30” indicates that all real numbers between “20–30” have been listed herein; “20–30” is simply an abbreviated representation of these numerical combinations.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0040] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0041] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, indicating that the method may include steps S1 and S2 performed sequentially, or it may include steps S2 and S1 performed sequentially. For example, the method may also include step S3, indicating that step S3 may be added to the method in any order. For example, the method may include steps S1, S2, and S3, or it may include steps S1, S3, and S2, or it may include steps S3, S1, and S2, etc.

[0042] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" may mean that other components not listed may also be included, or that only the listed components may be included. Additionally, in this application, the terms "a plurality of" or "multiple" refer to two or more types.

[0043] Unless otherwise specified, in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0044] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion. Unless otherwise stated, the terms used in this application have their commonly understood meanings as understood by one of ordinary skill in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0045] Currently, fast charging performance and long lifespan have become important performance indicators for lithium batteries. Ternary layered cathode active materials (such as NCM) are commonly used to prepare cathode sheets. However, with increasing cycle count and discharge time, this cathode material exhibits problems such as increased internal resistance and electrode polarization, leading to premature reaching of the discharge cutoff voltage. This results in a sharp drop in discharge voltage at the end of the discharge curve, affecting the battery's actual usable capacity. In other words, the cathode material in this system has poor rate tolerance at low SOC, impacting the battery's fast charging and cycle performance. Furthermore, while ternary layered cathode active materials (such as NCM) have high energy density, their cycle life and fast charging performance are not excellent.

[0046] In view of this, a first aspect of this application provides a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material including Li a Ni b Co c M 1d M 2e O fR' g , where 0.75 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is Mn element and / or Al element, M2 includes one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb; R' includes one or more elements of N, F, S, Cl; the second positive electrode active material includes Li 1+x M 3n Mn 1-y A' y P 1-z E z O4, where -0.100 ≤ x ≤ 0.100, 0 ≤ n ≤ 1.1, 0.001 ≤ y ≤ 0.500, 0 ≤ z ≤ 0.100, M3 includes one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W, A' includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb and Ge, E includes one or more elements of B, Si, N, S, F, Cl and Br; the positive electrode sheet satisfies:

[0047]

[0048] Where: 0.1 ≤ R ≤ 1.2; w (Mn) is the mass fraction of Mn in the positive electrode active material layer; d is the thickness of the positive electrode active material layer, in mm; T is the weight of the positive electrode active material layer per unit area of the positive electrode sheet, in g / cm 2 ; R is the resistance of the positive electrode sheet at 25 °C, in Ω. Among them, the dimension of the "mass fraction" described in this application is all 1.

[0049] Layered positive electrode active material system Li a Ni b Co c M 1d M 2e O f R' g has a poor rate tolerance boundary at low SOC, while the positive electrode active material Li 1+x M 3n Mn 1-y A' y P 1-z E z O4 has a low voltage discharge platform (generally not greater than 3.5V) at the end of discharge. By mixing it with the above-mentioned layered positive electrode active material, Li 1+x M 3n Mn1-y A′ y P 1-z E z The discharge plateau of O4 at low voltage causes a discharge plateau in the overall discharge curve of the blended composite cathode active material near the end. When the battery discharges to this plateau, the voltage change with capacity is relatively small, which is equivalent to a certain degree of constant voltage discharge on the layered cathode active material. This can alleviate the polarization effect during the previous discharge process at low voltage and improve the actual usable capacity. Furthermore, the cathode active material system Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 is also limited by its poor rate tolerance at high SOC levels. This can be addressed by combining it with a layered cathode active material system, Li. a Ni b Co c M 1d M 2e O f R′ g Blending can simultaneously compensate for the deficiencies of two systems, broaden the rate tolerance boundary at both high and low SOC levels, thereby improving fast charging capability while maintaining cycle performance; in addition, the positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ g Higher energy density, positive electrode active material Li 1+ x M 3n Mn 1-y A′ y P 1-z E z O4 offers superior cycle performance and safety. Furthermore, blending the two can further enhance the electrode's combination of high energy density and good cycle performance, extending its lifespan. Additionally, the positive electrode active material Li... 1+x M 3n Mn 1- y A′ y P 1-z E z O4 has a relatively large lattice shrinkage rate during charging and discharging. Blending the positive electrode active materials of the two systems is also beneficial for further matching the expansion of the battery negative electrode sheet and improving the long-term performance of the battery.

[0050] Furthermore, Li a Ni b Coc M 1d M 2e O f R′ g With Li 1+x M 3n Mn 1-y A′ y P 1-z E z After O4 incorporation, by controlling the Mn content, thickness, areal density, and resistance of the positive electrode active material layer to meet the above formula range, fast charging capability, energy density, and cycle performance can be simultaneously guaranteed, resulting in a fast-charging positive electrode with good cycle life. The reasons for this may include, but are not limited to, the coating quality of the positive electrode active material affecting Li... a Ni b Co c M 1d M 2e O f R′ g With Li 1+ x M 3n Mn 1-y A′ y P 1-z E z The mixing effect of O4, for example, can significantly improve electrode polarization when the coating quality of the positive electrode active material layer is too low. In this case, the mixing effect of O4 in Li... a Ni b Co c M 1d M 2e O f R′ g Medium-doped Li 1+x M 3n Mn 1-y A′ y P 1-z E z The improvement effect of O4 is not significant, and when the coating quality of the active material layer is too high, it will cause the polarization of the electrode to increase to a greater extent than that of Li doping. 1+ x M 3n Mn 1-y A′ y P 1-z E zThe improvement effect of O4; furthermore, the surface density of the positive electrode active material layer is related to its thickness and compaction density. When the surface density is determined, if the thickness of the positive electrode active material layer is too small, it means that the coating on the positive electrode sheet is too thin or the compaction density is too large. The former affects the energy density, and the latter affects the wetting of the electrode sheet by the electrolyte, which will deteriorate the cycle performance. If the thickness is too large, it means that the coating on the positive electrode sheet is too thick or the compaction density is too small. The former will increase the polarization of the electrode sheet and deteriorate the battery performance, and the latter will increase the contact resistance between particles in the electrode sheet and deteriorate the battery performance. In addition, if the resistance R of the positive electrode sheet is too high, it will also affect the power and cycle performance.

[0051] In this application, the mass fraction w of each element (such as A′ element, Mn element) in the positive electrode active material layer is... (A′)The mass of the positive electrode active material layer and the mass of the A′ element in the positive electrode active material layer can be determined separately and then calculated. The mass of the positive electrode active material layer can be obtained by disassembly and weighing (accurate to 0.0001g), and the mass of the A′ element in the positive electrode active material layer can be obtained by combining ICP testing. For example, the following steps can be taken: Take about 0.4g (accurate to 0.0001g) of dry positive electrode sheet or 0.1g (accurate to 0.0001g) of moist positive electrode sheet into a 30ml digestion vessel. Keep one digestion vessel without sample as a blank sample. Move the digestion vessel containing the positive electrode sheet sample into a fume hood and add 12ml of aqua regia. When adding the aqua regia, add it along the inner wall of the digestion vessel so that the residual sample on the inner wall is flushed to the bottom of the vessel. Then install the top cover, heat insulation sleeve, gasket, microwave digestion device, and nut in sequence. Tighten the nut with a wrench. Then turn on the microwave digestion device and microwave digestion. Insert the fiber optic sensor into the bottom of the previously assembled digestion vessel containing the sample. Place the digestion vessel evenly in the microwave digestion apparatus and begin digestion (digestion program: 6 min to 120℃, hold for 8 min; 5 min to 160℃, hold for 8 min; 5 min to 180℃, hold for 5 min). After digestion, cool to room temperature and remove the vessel. Place the digestion vessel in a fume hood and slowly loosen the nut to release the gas. Remove the previously assembled parts one by one. Transfer the solution from the digestion vessel to a 100 ml volumetric flask through a funnel (with filter paper underneath). Then rinse the digestion vessel with ultrapure water, transferring the rinsing solution into the volumetric flask as well. Use 10 ml of ultrapure water for each rinse. Shake the solution in the 100 ml volumetric flask well. Use a pipette to add 1 ml of the well-shaken solution to another 100 ml volumetric flask. Then add ultrapure water to make up to 100 ml of solution. Finally, test the sample solution using ICP-OES. To prepare aqua regia, pour 1000ml of ultrapure water into a 2500ml glass bottle, then add 750ml of concentrated nitric acid and 250ml of concentrated hydrochloric acid in sequence. Stir well and set aside. For the concentrated nitric acid, you can purchase a commercially available 68% concentrated nitric acid solution. For the concentrated hydrochloric acid, you can purchase a commercially available 68% concentrated hydrochloric acid solution, or you can add hydrogen chloride gas and ultrapure water in a mass ratio of 68% and 32% respectively. After the hydrogen chloride gas is completely dissolved, you can obtain the required concentrated hydrochloric acid.

[0052] In this application, the coating mass T of the positive electrode active material layer can be tested by weighing method, specifically by weighing the positive electrode active material layer within a fixed area (accurate to 0.0001g).

[0053] In this application, the resistance of the positive electrode sheet can be measured at room temperature using a BER1300 film resistance meter. The measurement steps can be as follows: (1) Prepare the electrode sheet into a round sheet with a diameter of 22 mm; (2) Place the prepared round sheet on the test platform of the BER1300 instrument; (3) Adjust the machine test pressure to 0.4 tons and the test time to 10 s, and then start the test. The obtained resistance value is the film resistance.

[0054] In this application, the thickness d of the active material layer of the positive electrode sheet can be measured by referring to the following method: Take a 1×2 cm area at the center of the electrode sheet, transfer it under a vacuum transfer device or an inert atmosphere protection environment, and then make a cross-section at low temperature using an argon ion beam milling (CP) device. After cutting, attach it to the cross-section sample stage with conductive tape and transfer it to the SEM vacuum chamber for sample observation. Adjust the appropriate parameters until the cross-sectional morphology can be clearly observed, and use the scanning electron microscope software to mark the thickness of the active material layer. Mark three regions respectively and take the average value as the thickness of the active material layer. 2 region, transfer it under a vacuum transfer device or an inert atmosphere protection environment, and then make a cross-section at low temperature using an argon ion beam milling (CP) device. After cutting, attach it to the cross-section sample stage with conductive tape and transfer it to the SEM vacuum chamber for sample observation. Adjust the appropriate parameters until the cross-sectional morphology can be clearly observed, and use the scanning electron microscope software to mark the thickness of the active material layer. Mark three regions respectively and take the average value as the thickness of the active material layer.

[0055] Furthermore, on the basis of meeting the above conditions, the positive electrode sheet of this application can further control the elemental mass fraction, the selection of the positive electrode active material, the electrode sheet resistance, the surface density and thickness of the positive electrode active material layer, etc. to further improve the performance of the positive electrode sheet. That is, on the basis of meeting the above conditions, one or more of the following conditions can also be optionally met.

[0056] In some embodiments of this application, a part of the first positive electrode active material can be Li a Ni b Co c M 1d M 2e O f Rˊ g , or it can all be Li a Ni b Co c M 1d M 2e O[[ID=​​​​​​​​​1d M 2e O f Rˊ g Meeting the above-mentioned conditions is more conducive to enabling the electrode and battery to have both high energy density, good cycle performance, and long cycle life. This is especially true for the positive electrode active material Li. a Ni b Co c M 1d M 2e O f Rˊ g Taking the nickel-cobalt-manganese ternary cathode active material (NCM) system as an example, increasing the nickel content can improve the volumetric energy density of the cathode material; increasing the manganese content can reduce the material cost, improve the material's safety and structural stability, and improve cycle performance, but excessively high manganese content will destroy the material's layered structure, reducing the material's specific capacity; cobalt can stabilize the material's layered structure and improve its cycle and rate performance, but excessively high cobalt content will lead to a decrease in actual capacity. By ensuring that the nickel, cobalt, and manganese contents meet the above-mentioned range conditions, it is beneficial to enable the electrode and battery to have higher energy density, better rate performance, and better cycle performance. Optionally, M1 can be Mn element, and the first cathode active material can be the cathode active material of the NCM system, in which case its general formula can be Li. a Ni b Co c Mn d M 2e O f Rˊ g For example, it can be a nickel-cobalt-manganese ternary layered positive electrode active material.

[0057] In some embodiments of this application, the second positive electrode active material may be partially Li 1+x M 3n Mn 1-y Aˊ y P 1-z E z O4, or all of it can be Li 1+x M 3n Mn 1-y Aˊ y P 1-z E zO4, wherein -0.100≤x≤0.100, 0≤n≤1.1, 0.001≤y≤1, 0≤z≤0.100, M3 includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W, Aˊ includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge, and E includes one or more elements selected from B, Si, N, S, F, Cl, and Br, doping at least one of the lithium, manganese, and phosphorus sites can help improve the performance of the positive electrode active material. For example, it can improve interface properties, reduce interfacial side reactions with the electrolyte, reduce the concentration of antisite defects, and improve the material's kinetic properties and specific capacity. At the same time, by controlling the doping elements at the manganese sites, the particle morphology can also be improved and the compaction density increased. Specifically, the above-mentioned second positive electrode active material can improve the performance of the positive electrode active material during charge and discharge. The lattice volume change rate of the cathode material is relatively large compared to the first positive electrode active material, which can better match the volume expansion of the negative electrode during charging. However, if the lattice volume change rate of the positive electrode material is too high, it will not be conducive to lithium-ion transport. The manganese doping element A' selected from the above elements helps to appropriately reduce the lattice change rate of the material during lithium insertion / extraction, improve the structural stability of the cathode material, reduce the dissolution of manganese elements and reduce the oxygen activity on the particle surface, thereby increasing the specific capacity of the material and reducing the interfacial side reactions between the material and the electrolyte during use, thus improving the cycle performance of the material. The phosphorus doping element E selected from the above elements also helps to change the ease of Mn-O bond length change, thereby improving electronic conductivity and reducing the lithium-ion migration barrier, promoting lithium-ion migration, and improving rate performance and fast charging performance. Similarly, the lithium doping element M3 selected from the above elements also helps to improve the lattice change rate of the material and maintain the capacity of the material. If the value of x is too small, it will lead to a decrease in the lithium content of the entire core system, affecting the specific capacity of the material. The y-value limits the total amount of all dopants, affecting the manganese content and voltage plateau of the material. When E is doped at the phosphorus position, a large z-value can negatively impact material stability due to the relatively stable tetrahedral structure of PO. When x, y, and z are selected from the above ranges, the cathode active material can exhibit better performance. Furthermore, the selection of the dopants and the x, n, y, and z values ​​can also improve the performance of Li… 1+x M 3n Mn 1-y Aˊ y P 1-z E zO4 maintains electrical neutrality, which helps minimize defects and impurities in the cathode active material. Taking lithium manganese phosphate as an example, if an excess of transition metal (e.g., manganese) is present, due to the relatively stable structure of the material system, the excess transition metal is likely to precipitate as elemental or form impurities within the crystal lattice. Maintaining electrical neutrality minimizes such impurities. Furthermore, maintaining system electrical neutrality can, in some cases, generate lithium vacancies in the cathode active material, thereby improving its kinetic performance. Compared to existing materials such as lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate, which are applicable to high-voltage systems, this method offers better cycle performance and high-temperature stability, as well as higher specific capacity and higher compaction density. It is understood that in the "manganese site" doping mentioned in this application, the manganese site only represents the Li-containing cathode active material. 1+x M 3n Mn 1-y Aˊ y P 1- z E z The location of manganese or Aˊ elements in the O4 lattice does not necessarily indicate the presence of manganese at those sites. Manganese at these sites can be partially or completely replaced by Aˊ elements. For example, when the y-value is 1, the second positive electrode active material Li... 1+x M 3n Mn 1-y Aˊ y P 1-z E z O4 does not contain manganese. For example, the manganese site may contain iron or iron and other doping elements.

[0058] In some embodiments of this application, the second positive electrode active material Li 1+x M 3n Mn 1-y Aˊ y P 1-z E z In O4, E can include one or more elements from B, Si, N and S. By selecting the element E that dopes the phosphorus site from the given range, it can further help to change the ease of Mn-O bond length changes, thereby improving electronic conductivity and reducing the lithium-ion migration barrier, promoting lithium-ion migration, and improving the rate performance and fast charging performance of the material.

[0059] In some embodiments of this application, the second positive electrode active material Li 1+x M 3n Mn 1-y Aˊ y P 1-z E zIn O4, A' can include one or more elements selected from Fe, Ti, V, and Mg. Optionally, A' can be Fe; further alternatively, A' can be at least two elements selected from Fe, Ti, V, and Mg; and still alternatively, A' can be Fe and one or more elements selected from Ti, V, and Mg. By selecting the manganese-doped element A' from the given range, the structural stability, specific capacity, cycle performance, and rate performance of the cathode material can be further improved, resulting in a cathode sheet with both good cycle life and fast-charging performance.

[0060] In some embodiments of this application, the second positive electrode active material Li 1+x M 3n Mn 1-y Aˊ y P 1-z E z In O4, doping can be performed simultaneously at manganese and phosphorus sites. This not only effectively reduces the dissolution of manganese elements, thereby reducing the number of manganese ions migrating to the negative electrode and decreasing electrolyte consumption due to SEI film decomposition, thus improving cycle performance and safety, but also promotes Mn-O bond adjustment, lowers the lithium-ion migration barrier, promotes lithium-ion migration, and improves rate performance and fast charging capability. Alternatively, doping can be performed simultaneously at lithium, manganese, and phosphorus sites, which can further result in significantly improved rate performance, improved cycle performance, and / or high-temperature stability.

[0061] In this application, the chemical formula of the first positive electrode active material is Li a Ni b Co c M 1d M 2e O f Rˊ g The chemical formula of the second positive electrode active material is Li 1+x M 3n Mn 1-y Aˊ y P 1-z E z O4, unless otherwise specified, when a doping site contains two or more elements, the limitation on the numerical range of the stoichiometric coefficients of the corresponding doping site elements in the chemical formula is not only a limitation on the stoichiometric coefficient of each element serving as that site, but also a limitation on the sum of the stoichiometric coefficients of all elements serving as that site. For example, taking the second positive electrode active material Li... 1+x M 3n Mn 1-y A′ y P 1-z E z Taking the chemical formula of O4 as an example, when A1′ consists of two or more elements A1′, A2′, ..., A nAt time ′, A1′, A2′……A n Each of their respective stoichiometric coefficients y1, y2, ... y n Each of them must fall within the numerical range of y as defined in this application, and y1, y2...y n The sum must also fall within this numerical range. Similarly, for cases where M3 or E consists of two or more elements, the numerical range of the stoichiometric coefficients of M3 and E in this application also has the above meaning.

[0062] In some embodiments of this application, The value range is 0.002 to 0.2, for example, it can be 0.0025, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, etc., or any range of the above values. Optionally, The value range can be 0.07 to 0.1, then 0.07 to 0.092, then 0.07 to 0.9, and then 0.07 to 0.8, through further control. Within the given range, a fast-charging positive electrode with a better cycle life can be obtained.

[0063] In some embodiments of this application, w (A′) w represents the mass fraction of A′ in the positive electrode active material layer. (P) The mass fraction of phosphorus (P) in the positive electrode active material layer, for example, The value can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, etc., or any range of the above values. Li a Ni b Co c M 1d M 2e O f R′ g With Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 doping is beneficial for improving the power capability at lower voltages and the cycle performance of the composite cathode. Furthermore, the power capability at both low and high voltages, as well as the cycle performance of the composite cathode, change with the doping ratio of O4 and Li. 1+x M 3n Mn 1-y A′y P 1-z E z When the O4 doping ratio is too high, it will affect the power capability at higher voltages, thereby deteriorating the power capability of the composite cathode. In this application, by... Keeping it within the given range is beneficial for Li a Ni b Co c M 1d M 2e O f R′ g With Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 has a suitable blending ratio, resulting in superior power capability and cycle performance of the composite cathode, better balancing fast charging performance and long service life. Optionally, optionally, By By keeping it within the given range, Li can be further optimized. a Ni b Co c M 1d M 2e O f R′ g and Li 1+x M 3n Mn 1-y A′ y P 1-z E z The mixing ratio of O4 was adjusted to obtain a fast-charging positive electrode with good cycle life.

[0064] In some embodiments of this application, the mass fraction of element A′ in the positive electrode active material layer satisfies: 0.01 ≤ w (A′) ≤0.05, for example, w (A′) The value can be 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, etc., or within any range of the above values. Increasing the content of element A′ in the second positive electrode active material helps improve cycle performance, but too high a content will damage the energy density. In this application, by further controlling the mass fraction of A′ in the positive electrode active material layer within the given range, it is possible to further balance cycle performance and high energy density while improving the fast charging performance of the positive electrode sheet, and extend the service life.

[0065] In some embodiments of this application, the second positive electrode active material may include lithium manganese phosphate system, lithium iron phosphate system, lithium manganese iron phosphate system, and all other materials conforming to the above general formula Li 1+x M 3n Mn1-y Aˊ y P 1-z E z One or more of the positive electrode active materials of O4, for example, the second positive electrode active material may include a positive electrode active material that satisfies at least one of the following two conditions: (i) 0.001≤y≤0.500, n=0, in which case the second positive electrode active material is Li 1+x Mn 1-y Aˊ y P 1-z E z O4, which can be lithium manganese phosphate with at least manganese doping, is used in this application to modify lithium manganese phosphate to significantly reduce manganese dissolution and lattice change rate. When used in secondary batteries, this improves cycle performance, rate performance, safety performance, and battery capacity. For example, by doping specific elements at the lithium, manganese, and phosphorus sites of the compound LiMnPO4 in specific amounts, it is beneficial to obtain improved rate performance, while reducing the dissolution of Mn and Mn-doped elements, thus achieving improved cycle performance and / or high-temperature stability. Furthermore, the specific capacity and compaction density of the positive electrode active material can also be improved. As a specific example, Li... 1+x Mn 1-y Aˊ y P 1-z E z O4 may include Li 1+x Mn 1-y Fe y P 1-z E z O4, compared to lithium iron phosphate, lithium manganese iron phosphate has a higher voltage plateau and a higher energy density for the same specific capacity; (ii) 0.001≤y≤0.500, 0.9≤n≤1.1, in this case the second positive electrode active material is Li 1+x M 3n Mn 1-y Aˊ y P 1-z E z For the second positive electrode active material in the lithium manganese phosphate system, considering that the y value limits the total amount of all doping elements, if y is too small (i.e., the doping amount is too low), the doping elements will not play a role. If y exceeds 0.5, it will lead to a low Mn content in the system, affecting the voltage plateau of the material. The range of y can be selected from 0.001 to 0.500, and further from 0.25 to 0.5. It should be noted that the chemical formula Li involved in the above two conditions... 1+x Mn 1-y Aˊ y P 1-z E z O4 and Li 1+xM 3n Mn 1-y Aˊ y P 1-z E z In O4, elements located at the same site can have the same or different stoichiometric coefficients, but all satisfy the chemical formula Li. 1+x M 3n Mn 1-y Aˊ y P 1-z E z The numerical range of stoichiometric coefficients for each element in O4.

[0066] As a specific example, the second positive electrode active material may include a positive electrode active material that satisfies the following conditions: 0.001≤y≤0.500, n=0, and the second positive electrode active material is Li. 1+x Mn 1-y Aˊ y P 1-z E z O4. Optionally, the second positive electrode active material may consist only of Li. 1+x Mn 1-y Aˊ y P 1-z E z O4 is the positive electrode active material. Optionally, A' may include Fe, for example, it may be only Fe.

[0067] In some embodiments of this application, the weight T (in g / cm³) of the positive electrode active material layer per unit area of ​​the positive electrode sheet is... 2 The following condition must be met: 0.032 ≤ T ≤ 0.043. For example, T can be 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, 0.040, 0.041, 0.042, etc., or within any range of the above values. The coating quality of the positive electrode active material layer not only affects the polarization of the electrode but also the energy density of the electrode. Under the premise of satisfying the relationship between the content of A' element in the positive electrode active material layer, the thickness and areal density of the positive electrode active material layer, and the resistance of the positive electrode, this application can further improve the fast charging performance and cycle life, as well as the energy density and extend the service life by further controlling the areal density T of the positive electrode active material layer within the given range. Optionally, 0.035 ≤ T ≤ 0.039, further controlling T within the given range can further enable the positive electrode to achieve both good fast charging capability and long service life.

[0068] In some embodiments of the present application, the thickness d (unit: mm) of the positive electrode active material layer satisfies: 0.11 ≤ d ≤ 0.16. For example, the value of d can be 0.115, 0.12, 0.125, 0.13, 0.135, 0.14, 0.145, 0.15, 0.155, etc., or within any range of any of the above values. The thickness of the positive electrode active material layer not only affects the energy density of the battery, but also affects its cycling performance and fast charging performance. On the premise of satisfying the relationship formula of the content of element A' in the positive electrode active material layer, the thickness and surface density of the positive electrode active material layer, and the resistance of the positive electrode sheet, by further controlling the thickness d of the positive electrode active material layer within the given range, improved fast charging performance and cycle life, as well as a higher energy density can be further obtained simultaneously, and the service life can be extended. Optionally, 0.12 ≤ d ≤ 0.14. Further controlling d within the given range can further enable the positive electrode sheet to have better fast charging ability and long service life.

[0069] In some embodiments of the present application, the resistance R (unit: Ω) of the positive electrode sheet satisfies: 0 < R ≤ 1.2. For example, the value of R can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, etc., or within any range of any of the above values. Considering that too high resistance of the positive electrode sheet will also affect the power performance and cycling performance of the battery, by controlling the value range of R within the given range, it can be further beneficial to enable the electrode sheet to have better fast charging performance and cycling performance. Optionally, 0.1 ≤ R ≤ 1. By further controlling the value range of R within the given range, the internal resistance of the electrode sheet can be further reduced, and the fast charging performance and cycling performance can be improved.

[0070] In some embodiments of the present application, the mass fractions of Mn element and A' element in the positive electrode active material layer can also satisfy the following conditions: w (Mn) is the mass fraction of manganese in the positive electrode active material layer. For example The value of can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, etc., or within any range of any of the above values. The content of element A' in the second positive electrode active material affects the voltage platform and cycling performance of the material. A higher content of element A' helps to improve the cycling performance, but there will be an obvious loss in the platform voltage, which is not conducive to the energy density of the battery. For example, as a specific example, when both manganese element and iron element are contained at the manganese site, a higher manganese-iron ratio can increase the voltage platform, which is beneficial to improving the energy density of the battery. However, when the manganese-iron ratio is too high, a large amount of trivalent manganese in the delithiated state may damage the solid solution structure, reduce the specific capacity and cycling capacity retention rate of the material, resulting in poor cycling performance and affecting the life of the positive electrode. In the present application, by controlling Within the given range, the value of A′ can be used to ensure a suitable range of A′ element content in the second positive electrode active material. This allows for improved fast charging capability while also maintaining high energy density and good cycle performance, thus extending service life. Optionally, Alternatively, This allows for higher energy density, improved fast charging performance, and longer lifespan.

[0071] As a specific example, the first positive electrode active material can be Li, the positive electrode active material of the NCM system. a Ni b Co c Mn d M 2e O f R′ g If it can be Li a Ni b Co c Mn d O f R′ g The second positive electrode active material can be Li 1+x Mn 1-y A′ y P 1-z E z O4 (0.001≤y≤0.500), could be Li 1+x Mn 1-y Fe y P 1-z E z O4, at this time The value range can be 3 to 20, can be selected as 4 to 18, and can be further selected as 5 to 17; furthermore, The value range of w can be 0.27 to 1.63, and can be selected as 0.72 to 1.26; furthermore, w (A′) The value can be between 0.01 and 0.05. In this application, by making the positive electrode meet the given conditions, improved fast charging performance, cycle performance, and long service life can be obtained.

[0072] In some embodiments of this application, the positive electrode can simultaneously satisfy the following two conditions: Optionally, The content of Mn and A′ elements in the positive electrode active material layer, especially in the second positive electrode active material, directly or indirectly affects the fast-charging capability and cycle life of the composite positive electrode. The change in the value, The range of values ​​for will also change accordingly, when and When the value of satisfies the given range, the composite cathode can be further made to have better power capability and better cycle life.

[0073] In some embodiments of this application, the Dv50 particle size of the first positive electrode active material is 2.1 μm to 6.3 μm, for example, it can be 2.4 μm, 2.7 μm, 3.0 μm, 3.3 μm, 3.6 μm, 3.9 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.1 μm, 5.4 μm, 5.7 μm, 6.0 μm, or any range of the above values. The Dv50 of the first positive electrode active material refers to the particle size corresponding to when the cumulative volume distribution percentage of the first positive electrode active material reaches 50%. In this application, the Dv50 particle size of the first positive electrode active material can be determined by laser diffraction particle size analysis, for example, by referring to standard GB / T 19077-2016 and using a laser particle size analyzer (e.g., Malvern Master Size 3000). In this application, by controlling the Dv50 particle size of the first positive electrode active material within a given range, it is not only beneficial to prevent breakage or pulverization during charging and discharging, thereby reducing capacity loss, but also to shorten the diffusion path of active ions and increase the electron conduction rate, which is beneficial to improving cycle performance. Simultaneously, it can also ensure that the active material has suitable active sites, reducing or avoiding the negative impact on cycle performance caused by excessively small particle size leading to a large number of active sites and increased side reactions during cycling, and the negative impact on power performance caused by excessively large particle size leading to fewer active sites. Optionally, the Dv50 particle size of the first positive electrode active material can be 3.5 μm to 4.9 μm, thereby further balancing high energy density, good power performance, and cycle performance, improving fast charging capability and lifespan.

[0074] In some embodiments of this application, the Dv50 particle size of the second positive electrode active material can be 0.21 μm to 1.53 μm, for example, 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, etc., or any range of the above values. The Dv50 of the second positive electrode active material refers to the particle size corresponding to a cumulative volume distribution percentage of 50% for the second positive electrode active material. In this application, the Dv50 particle size of the second positive electrode active material can be determined by laser diffraction particle size analysis, for example, by referring to standard GB / T 19077-2016 and using a laser particle size analyzer (e.g., Malvern Master Size 3000). In this application, by controlling the Dv50 particle size of the second positive electrode active material within a given range, it not only helps prevent breakage or pulverization during charging and discharging, thereby reducing capacity loss, but also shortens the diffusion path of active ions and increases the electron conduction rate, which is beneficial for improving cycle performance. Simultaneously, it ensures that the active material has suitable active sites, balancing both cycle performance and power performance. Furthermore, controlling the Dv50 particle size of the second positive electrode active material within the given range also helps to achieve the expected compaction density by matching the Dv50 particle size range of the first positive electrode active material, avoiding large gaps between the positive electrode active material particles. Optionally, the Dv50 particle size of the second positive electrode active material can be 0.5 μm to 0.9 μm, thereby further balancing high energy density, good power performance, and cycle performance, improving fast charging capability and lifespan.

[0075] In some embodiments of this application, the specific surface area of ​​the first positive electrode active material can be 0.3 m². 2 / g~1.2m 2 / g, for example, can be 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, or any value within any range mentioned above; optionally, the specific surface area of ​​the first positive electrode active material can be 0.5m². 2 / g~0.9m 2 / g. Furthermore, the specific surface area of ​​the second positive electrode active material can be 9.2m². 2 / g~23.6m 2 / g, for example, can be 10m 2 / g、11m2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g, or any value within any range mentioned above; optionally, the specific surface area of ​​the second positive electrode active material is 10.5m². 2 / g~19.6m 2 / g, or 12.0m 2 / g~16.2m 2 / g, or alternatively 10.0m 2 / g~21.5m 2 / g, or 10.9m. 2 / g~17.6m 2 / g. In this application, the specific surface area of ​​the first and second positive electrode active materials can be measured using conventional methods in the art, such as nitrogen physical adsorption. Increasing the specific surface area helps to increase the active sites of the positive electrode active material, giving the material better power performance. However, these increased active sites also increase the side reactions of the positive electrode active material during cycling, thereby causing the material's cycle performance to decline. In this application, by controlling the specific surface area of ​​the first and second positive electrode active materials within a given range, better power performance and cycle life can be further obtained, improving fast charging capability and service life.

[0076] As a specific example, when the positive electrode active material layer is satisfy At this time, the Dv50 particle size of the second positive electrode active material can be 0.21 μm to 1.53 μm, and its specific surface area can be 9.2 m². 2 / g~23.6m 2 / g; further, when satisfy When the particle size of the second positive electrode active material is 0.38 μm to 1.10 μm, and can be selected as 0.47 μm to 0.91 μm, the specific surface area of ​​the second positive electrode active material can be 10.5 m². 2 / g~19.9m 2 / g, optional 12.0m 2 / g~16.2m 2 / g; further, when satisfy When the particle size of the second positive electrode active material is 0.32 μm to 1.40 μm, and can be selected as 0.41 μm to 1.25 μm, the specific surface area of ​​the second positive electrode active material can be 10.0 m². 2 / g~21.5m 2 / g, optional 10.9m 2 / g~17.6m 2 / g. Variations in the Dv50 particle size and specific surface area of ​​the second positive electrode active material both affect the material's power performance and cycle life, and different... The corresponding optimal Dv50 particle size and specific surface area ranges are also different, by making The Dv50 particle size and specific surface area of ​​the second positive electrode active material meet the above-mentioned range conditions, which can further enable the composite positive electrode to have better cycle life while having better power capability.

[0077] In some embodiments of this application, the surface of the first positive electrode active material may be provided with a first coating layer. Optionally, the first coating layer may include one or more elements selected from Ti, Al, B, Nb, Zr, Si, and W. Providing a coating layer on the surface of the positive electrode active material not only prevents the positive electrode active material from contacting the electrolyte, thereby reducing side reactions between the positive electrode active material and the electrolyte, but also improves the structural stability of the positive electrode active material, thereby improving the material's cycle stability and safety. Furthermore, the aforementioned elements in the first coating layer can be provided in oxide form (such as Al2O3, ZrO2, TiO2, Nb2O3, etc.) or in the form of lithium compounds, etc., so that the first coating layer contains the given element range, which can improve the ionic conductivity of the material surface, improve the material's rate performance and specific capacity, stabilize the material structure, prevent direct contact between the material and the electrolyte, and improve cycle performance.

[0078] In some embodiments of this application, the thickness of the first coating layer can be 20nm to 150nm, for example, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, or any value within any range mentioned above. When the thickness of the first coating layer is too thin, the possibility of cracking / deep damage during the use of the positive electrode active material increases, resulting in a significant reduction in its performance enhancement and protection of the first positive electrode active material. When the thickness of the first coating layer is too thick, lithium ions require a longer transport path to reach the active material system from the electrolyte, which has a significant impact on the performance of the active material. In addition, during the sintering of the coating layer, the coating material reacts with the lithium in the internal material, resulting in a reduction in the available active lithium in the material and a corresponding decrease in the specific capacity of the material. By controlling the thickness of the first coating layer within the range given above, this application can effectively avoid or reduce the above problems, effectively improve the rate performance of the first positive electrode active material, and stabilize the surface structure of the material. Meanwhile, based on the Dv50 particle size of the first positive electrode active material, controlling the thickness of the first coating layer within the given range is also beneficial to further enable the composite positive electrode to obtain a high energy density.

[0079] In some embodiments of this application, a second coating layer may be provided on the surface of the second positive electrode active material. The second coating layer not only prevents the second positive electrode active material from contacting the electrolyte, thereby reducing side reactions between the two, but also prevents or inhibits the dissolution of transition metals or dopants in the second positive electrode active material, while improving its structural stability, thus enhancing the cycle stability and safety of the positive electrode active material. Optionally, the second coating layer may include at least one of pyrophosphate, phosphate, and carbon. Metal ions are difficult to migrate in pyrophosphate; selecting pyrophosphate as the coating layer material can effectively isolate the metal ions doped in the positive electrode material from the electrolyte. Further, the pyrophosphate may be selected as crystalline pyrophosphate, as crystalline pyrophosphate has a stable structure and, as a coating layer material, is beneficial for effectively inhibiting the dissolution of transition metals in the active material and improving cycle performance. Phosphate coating can improve the ion transport performance of cathode materials, which is beneficial for promoting lithium-ion transport. Furthermore, phosphates can be crystalline phosphates. Crystalline phosphates and crystalline pyrophosphates have high lattice matching, good stability, and excellent lithium-ion conductivity. Coating the second cathode active material with phosphates can improve the stability of the cathode active material, effectively reducing interfacial side reactions in the electrolyte, thereby improving the battery's high-temperature cycling and storage performance. Carbon coating can effectively improve the conductivity and desolvation capability of cathode active materials. Carbon materials have good electronic conductivity. When used in batteries, electrochemical reactions occur, requiring the participation of electrons. To increase electron transport between particles and between different positions on the particles, carbon with excellent conductivity can be used to coat the cathode active material. It is understandable that when the second coating layer includes pyrophosphate, phosphate and carbon, the pyrophosphate, phosphate and carbon can be located in the same coating layer or in at least two sub-coating layers. For example, a pyrophosphate coating layer, a phosphate coating layer and a carbon coating layer can be formed sequentially on the surface of the second positive electrode active material, or a phosphate coating layer, a pyrophosphate coating layer and a carbon coating layer can be formed sequentially on the surface of the second positive electrode active material, or a composite coating layer of pyrophosphate and phosphate can be formed first on the surface of the second positive electrode active material, and then a carbon coating layer can be formed on the surface of the composite coating layer.

[0080] In some embodiments of this application, the thickness of the second coating layer can be from 10 nm to 50 nm. For example, it can be 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, etc., or within any range of the above values. Controlling the thickness of the second coating layer within the given range can not only effectively hinder the dissolution of transition metals or dopants in the second positive electrode active material and reduce the lattice change rate of the second positive electrode active material, but also prevent excessive coating thickness from affecting lithium ion migration and battery energy density. Thus, without sacrificing the specific capacity of the second positive electrode active material, the kinetic performance, cycle performance, and safety of the battery can be further improved.

[0081] As a specific example, the second coating layer may include a first sub-coating layer, a second sub-coating layer, and a third sub-coating layer. The first sub-coating layer may coat the second positive electrode active material and include crystalline pyrophosphate. The second sub-coating layer may include crystalline phosphate and coat the first sub-coating layer. The third sub-coating layer may be carbon and coat the second sub-coating layer. Pyrophosphate, as the first sub-coating layer, can effectively isolate the metal ions doped in the second positive electrode active material from the electrolyte. The crystalline pyrophosphate coating is beneficial for effectively suppressing the dissolution of transition metals in the second positive electrode active material and improving cycle performance. The crystalline phosphate, as the second sub-coating layer, has a higher lattice matching degree with the crystalline pyrophosphate in the first sub-coating layer, and its stability is better than that of pyrophosphate, exhibiting excellent lithium-ion conductivity, which is beneficial for improving the stability of the positive electrode active material and reducing interfacial side reactions between the positive electrode active material and the electrolyte. The third sub-coating layer can enhance electron transport between particles, improve the electronic conductivity of the positive electrode active material, and effectively improve the conductivity and desolvation capability of the positive electrode active material. Furthermore, the thickness of the first sub-coating layer can be 1 nm to 10 nm, such as 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, etc., or within any range of the above values. When the thickness of the first sub-coating layer is within the given range, it helps to avoid the adverse effects on the kinetic performance of the positive electrode active material that may occur when it is too thick, and it also helps to avoid the problem that it may not be able to effectively hinder the migration of transition metal ions when it is too thin. The thickness of the second sub-coating layer can be 2 nm to 15 nm, such as 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, etc., or within any range of the above values. If the thickness of the second sub-coating layer is too large, it may... The plateau voltage of the positive electrode active material is affected by the thickness of the second sub-coating layer. When the thickness of the second sub-coating layer is within the given range, its surface structure is stable, and the side reactions with the electrolyte are small, which helps to effectively reduce interfacial side reactions and thus improve the high-temperature cycle performance and high-temperature storage performance of the battery. The thickness of the third sub-coating layer can be 2nm to 25nm, such as 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, etc., or any value within any range of the above. When the thickness of the third sub-coating layer is within the given range, it helps to improve the conductivity of the positive electrode active material and increase the compaction density of the positive electrode sheet. At the same time, it avoids the problem of the compaction density of the electrode sheet being affected by excessive coating thickness when the sub-coating layer contains amorphous carbon.

[0082] In this application, the thickness of each coating layer can be tested by FIB. The specific method may include the following steps: randomly select a single particle from the positive electrode active material powder to be tested, cut a thin slice with a thickness of about 100 nm from the middle position or near the middle position of the selected particle, and then perform TEM testing on the thin slice to measure the thickness of the coating layer. Measure 3 to 5 positions and take the average value.

[0083] A second aspect of this application provides a secondary battery comprising: a positive electrode sheet according to the first aspect of this application.

[0084] In a secondary battery, a typical assembly includes a casing, a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, separator, and electrolyte are located within a cavity formed by the casing assembly. Depending on the battery type, the casing assembly can be an aluminum-plastic film or a metal casing assembly, etc. Metal casing assemblies can include square casing assemblies and cylindrical casing assemblies. When the casing assembly is a metal casing assembly, it typically includes a casing with an opening on at least one side and a cover for sealing the opening. Regardless of the battery type, as long as its positive electrode includes the positive electrode of the first aspect of this application, it can be understood as being included within the technical scope of the battery of the fourth aspect of this application. Except for the aforementioned characteristics such as the active material and compaction density of the active material layer of the positive electrode, other structural features or material selections of the positive electrode, as well as the selection of the negative electrode, separator, and electrolyte, can adopt conventional choices in the art, and those skilled in the art can flexibly choose according to actual needs.

[0085] In some embodiments of this application, the secondary battery can be either a stacked battery or a wound battery. The wound battery can be either a prismatic battery or a cylindrical battery, and optionally, it can be a cylindrical battery. Depending on the battery type, the positive electrode, negative electrode, and separator can be stacked to form a stacked unit, or they can be stacked and then wound to form a wound body.

[0086] In some embodiments of this application, the battery can be a single cell or a battery module assembled from cells. The number of cells included in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Furthermore, the battery module may also include a packaging assembly with a receiving space, which may include a base plate, side plates, and a cover plate, etc.

[0087] In some embodiments of this application, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0088] In addition, this application also provides an electrical device, which includes: a positive electrode plate of the first aspect of this application, and / or a secondary battery of the second aspect of this application.

[0089] The secondary battery, such as a cell, module, or pack, can serve as both a power source and an energy storage unit for the electrical device. This electrical device can include, but is not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, and energy storage systems. As a specific example, the electrical device can be a vehicle.

[0090] Electrical devices can choose the specific type of battery according to their usage needs, such as battery cells, battery modules, or battery packs.

[0091] As an example, the electrical device can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery, a battery pack or battery module can be used.

[0092] As another example, the device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use battery cells as their power source.

[0093] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0094] Preparation and testing methods for secondary batteries:

[0095] 1. Soft-pack laminated battery:

[0096] ① Preparation of positive electrode sheet:

[0097] Positive electrode active material, polyvinylidene fluoride (PVDF), and conductive carbon are added to a certain amount of N-methylpyrrolidone (NMP). The mass ratio of positive electrode active material: polyvinylidene fluoride: conductive carbon is 90:5:5. The mixture is stirred in a drying room to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·s. The slurry is then coated onto aluminum foil and dried to form a positive electrode sheet.

[0098] ② Preparation of negative electrode sheet:

[0099] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon are added to a certain amount of deionized water. The mass ratio of graphite:sodium carboxymethyl cellulose:styrene-butadiene rubber:conductive carbon is 90:2:3:5. The mixture is stirred to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·s. The slurry is then coated onto copper foil and dried to form a negative electrode sheet.

[0100] ③ Fabrication of pouch cells:

[0101] The prepared positive electrode, negative electrode, and separator (polyethylene (PE) porous polymer film) are stacked in a Z-shaped structure to form the corresponding battery cell. The battery cell is vacuum dried at 90℃ for 12 hours, followed by ultrasonic welding of the positive and negative electrode tabs. The positive electrode uses aluminum tabs and the negative electrode uses nickel tabs, with the positive and negative electrode tabs located on the same side of the battery cell. The battery cell with the tabs welded is then placed into an aluminum-plastic film of appropriate size for top-side sealing. The sealing temperature is 145℃. Electrolyte is injected (the electrolyte is 1 mol / L LiPF6 / (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1) + 5 wt.% fluoroethylene carbonate (FEC)). After standing, formation, aging, venting, resealing, and capacity testing, the prepared soft-pack stacked battery is obtained.

[0102] 2. Cyclic testing was performed on the prepared pouch-pack laminated battery at 25℃:

[0103] The prepared pouch cell was charged at 0.5C0 to 4.4V under a constant temperature environment of 2.5–4.4V, and then charged at a constant voltage of 4.4V until the current ≤0.05C0. After standing for 5 minutes, it was discharged at 1C0 to 2.5V. The capacity is recorded as C. n (n = 1, 2, 3...), repeat the above operation, with the capacity retention rate according to C... n The ratio of / C3 is calculated when C n When / C3×100%=80%, the corresponding number of cycles is extracted as an indicator of cycle capability.

[0104] 3. Positive electrode film resistance test:

[0105] The membrane resistance was tested using a BER1300 membrane resistance meter. The test steps were as follows: (a) Prepare the electrode into a 22mm diameter disc; (b) Place the prepared disc onto the test platform of the BER1300 instrument; (c) Adjust the machine test pressure to 0.4T, the test temperature to 25℃, and the test time to 10s, and start the test. The obtained resistance value is the membrane resistance.

[0106] 4. Charging time experiment from 10% to 80% SOC:

[0107] First, the capacity of the pouch-type laminated battery is tested. The procedure is as follows: constant current charging at 0.33C to the full charge voltage V1, then constant voltage charging. When the charging current decreases to 0.05C, the constant voltage charging ends. Then, discharge at 0.33C to the full discharge voltage V2. This procedure is repeated 3 times, and the capacity result of the 3rd test is taken as the standard. The specific capacity of the positive electrode can also be calculated using the 3rd result.

[0108] Different rate (C1) tests were conducted on pouch cells. <C2<C3<C4<……<C n The charging test requires the charging rate to be gradually increased, and the total voltage and negative electrode voltage of the pouch cell must be monitored simultaneously during charging. The detailed process is as follows: Charge the pouch cell at C1 to the full charge voltage V1 or the negative electrode voltage to 0V. Extract the SOC value at the end of charging. Then discharge at 0.33C to the full discharge voltage V2. Repeat the above process to obtain the SOC value at the end of charging at different rates. Plot a scatter plot of SOC vs. charging rate at the end of charging, and fit the relationship between SOC and charging rate. Substitute 20%, 30%, 40%, 50%, 60%, 70%, and 80% into the relationship to obtain the corresponding charging rate (C). 20％ C 30％ C 40％ C 50％ C 60％ C 70％ C 80％ Then you can calculate the charging time from 10% to 80% SOC: 10% to 80% SOC charging time = (60 / C) 20％ +60 / C 30％ +……+60 / C 80％ )×10%.

[0109] Example 1

[0110] In pouch cells:

[0111] (i) Positive electrode: The number of positive electrode layers is 15; the thickness of a single positive electrode layer is 0.13 mm; the weight of the positive electrode active material layer per unit area of ​​the positive electrode is 0.038 g / cm³. 2 The first positive electrode active material is NCM523, with a Dv50 particle size of 4.2 μm and a specific surface area of ​​0.5 m². 2 / g; The second positive electrode active material is LiMn 0.6 Fe 0.4 The PO4 second positive electrode active material has a Dv50 particle size of 0.8 μm and a specific surface area of ​​13.3 m². 2 / g; the positive electrode plate satisfies: A′ is Fe, The electrode resistance is 0.7Ω.

[0112] (ii) Negative electrode: The negative electrode has 16 layers; the thickness of a single negative electrode layer is 0.13 mm; the weight of the negative electrode active material layer per unit area is 0.012–0.030 g / cm³. 2 .

[0113] (iii) Diaphragm: The diaphragm has 16 layers; the thickness of a single diaphragm layer is 0.012 mm.

[0114] (iv) The inner thickness of the battery casing is 6.1 mm.

[0115] (v) The electrolyte injection coefficient of the secondary battery is 2.84 g / Ah.

[0116] Examples 2-15 and Comparative Examples 1-3

[0117] The difference between Examples 1-9 and Comparative Examples 1-3 and Example 1 is that: in the positive electrode sheet... The range of values ​​is different, and this difference is achieved by changing the mixing ratio of the first positive electrode active material and the second positive electrode active material, as detailed in Table 1.

[0118] The difference between Examples 10-15 and Example 1 is that the types of the second positive electrode active materials are different, as detailed in Table 1.

[0119] The batteries assembled in Examples 1-15 and Comparative Examples 1-3 were tested, and the test results are detailed in Table 1.

[0120] Table 1. Differences between Examples 1-15 and Comparative Examples 1-3, and related test results.

[0121]

[0122]

[0123] Results and conclusions:

[0124] As can be seen from the above embodiments and comparative examples, the battery design scheme of this application can improve the fast charging performance and cycle performance of the battery. Specifically, as can be seen from embodiments 1-9 and comparative examples 1-3, when the first positive electrode active material and the second positive electrode active material are determined, the resistance of the positive electrode sheet, the content of Mn element in the electrode sheet, and the relative amount of Mn element and A′ element (Fe element in the above embodiments) change with the mixing ratio of the two. The values ​​will change accordingly; as can be seen from Examples 1 and 10-15, the change in the type of the second positive electrode active material will also affect the resistance of the positive electrode, the content of Mn element in the electrode, and the relative amount of Mn element and A′ element (Fe element in the above examples), and The value of . But overall, When the value of Mn is in the range of 0.002 to 0.2, the battery's fast charging performance and cycle performance are relatively good; a value of 0.03 to 0.085 can be selected. Based on this, the relative amounts of Mn and Fe elements in the positive electrode sheet... The value can be selected from 3 to 20, and can also be selected from 5 to 17.

[0125] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive electrode active material layer, which comprises a first positive electrode active material and a second positive electrode active material. The first positive electrode active material includes Li a Ni b Co c M 1d M 2e O f R´ g , where 0.75 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, M1 is Mn element and / or Al element, M2 includes one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, etc., and R´ includes one or more elements selected from N, F, S, Cl, etc.; The second positive electrode active material includes Li 1+x M 3n Mn 1-y A´ y P 1-z E z O4, wherein -0.100≤x≤0.100, 0≤n≤1.1, 0.001≤y≤0.500, 0≤z≤0.100, M3 includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, A´ includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb and Ge, and E includes one or more elements selected from B, Si, N, S, F, Cl and Br; The positive electrode plate satisfies: ， in: 0.1≤R≤1.2； w (Mn) The mass fraction of Mn in the positive electrode active material layer; d represents the thickness of the positive electrode active material layer, in mm; T represents the weight of the positive electrode active material layer per unit area of ​​the positive electrode sheet, in g / cm³. 2 ; R is the resistance of the positive electrode at 25°C, in Ω.

2. The positive electrode sheet according to claim 1, characterized in that, , where w (A´) w is the mass fraction of A' in the positive electrode active material layer. (P) The mass fraction of P in the positive electrode active material layer.

3. The positive electrode sheet according to claim 2, characterized in that, 。 4. The positive electrode sheet according to claim 2 or 3, characterized in that, 0.01≤w (A´) ≤0.05。 5. The positive electrode sheet according to claim 1, characterized in that, The second positive electrode active material includes at least one of the following two positive electrode active materials: (i) 0.001≤y≤0.500, n=0, the second positive electrode active material is Li 1+x Mn 1-y A´ y P 1-z E z O4; (ii) 0.001≤y≤0.500, 0.9≤n≤1.1, the second positive electrode active material is Li 1+x M 3n Mn 1-y A´ y P 1- z E z O4.

6. The positive electrode sheet according to claim 1, characterized in that, 0.032≤T≤0.043。 7. The positive electrode sheet according to claim 6, characterized in that, 0.035≤T≤0.039。 8. The positive electrode sheet according to claim 1, characterized in that, 0.11≤d≤0.16。 9. The positive electrode sheet according to claim 8, characterized in that, 0.12≤d≤0.14。 10. The positive electrode sheet according to claim 1, characterized in that, 0.1≤R≤1。 11. The positive electrode sheet according to claim 1, characterized in that, M1 is an element of Mn.

12. The positive electrode sheet according to claim 1, characterized in that, At least one of the following conditions must be met: 3≤ ≤20； The Dv50 particle size of the second positive electrode active material is 0.21 μm ~ 1.53 μm; The specific surface area of ​​the second positive electrode active material is 9.2 m². 2 / g ~23.6m 2 / g; where w (A´) The mass fraction of A' in the positive electrode active material layer.

13. The positive electrode sheet according to claim 12, characterized in that, 5≤ ≤17， 。 14. The positive electrode sheet according to claim 13, characterized in that, 。 15. The positive electrode sheet according to claim 1, characterized in that, The Dv50 particle size of the first positive electrode active material is 2.1 μm ~ 6.3 μm.

16. The positive electrode sheet according to claim 1, characterized in that, The Dv50 particle size of the first positive electrode active material is 3.5 μm ~ 4.9 μm.

17. The positive electrode sheet according to claim 1, characterized in that, The specific surface area of ​​the first positive electrode active material is 0.3 m². 2 / g ~1.2m 2 / g.

18. The positive electrode sheet according to claim 17, characterized in that, The specific surface area of ​​the first positive electrode active material is 0.5 m². 2 / g ~0.9m 2 / g.

19. The positive electrode sheet according to claim 1, characterized in that, The surface of the first positive electrode active material is provided with a first coating layer, which includes one or more elements selected from Ti, Al, B, Nb, Zr, Si and W.

20. The positive electrode sheet according to claim 19, characterized in that, The thickness of the first coating layer is 20nm to 150nm.

21. The positive electrode sheet according to claim 1, characterized in that, The surface of the second positive electrode active material is provided with a second coating layer, the second coating layer comprising at least one of pyrophosphate, phosphate and carbon.

22. The positive electrode sheet according to claim 21, characterized in that, The thickness of the second coating layer is 10nm to 50nm.

23. The positive electrode sheet according to claim 1, characterized in that, In the second positive electrode active material, E includes one or more elements selected from B, Si, N, and S.

24. The positive electrode sheet according to claim 1, characterized in that, In the second positive electrode active material, A' includes one or more elements selected from Fe, Ti, V and Mg.

25. A secondary battery, characterized in that, The positive electrode sheet includes any one of claims 1 to 24.

26. An electrical appliance, characterized in that, Includes the positive electrode sheet according to any one of claims 1 to 24, and / or the secondary battery according to claim 25.

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