Positive electrode sheet, secondary battery, and electric device

Abstract

The invention discloses a positive plate, a secondary battery and an electric device. Wherein the positive plate comprises a positive active material layer, the positive active material layer comprises a first positive active material and a second positive active material, the first positive active material comprises LiaNibCocM1dM2eOfR'g, and a is more than or equal to 0.75 and less than or equal to 1.2, 0lt; blt; 1, 0lt; clt; ct; 1, 0lt; dlt; 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 comprises Li1 + xM3nMn1-yA'yP1-zEzO4, x is greater than or equal to-0.100 and less than or equal to 0.100, n is greater than or equal to 0 and less than or equal to 1.1, y is greater than or equal to 0.001 and less than or equal to 0.500, z is greater than or equal to 0 and less than or equal to 0.100, and A'comprises one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb and Ge; the positive plate meets the formula: # imgabs0 #, wherein R is more than or equal to 0.1 and less than or equal to 1.2; w (Mn) is the mass fraction of Mn in the positive electrode active material layer; d is the thickness of the positive active material layer, and the unit is mm; t is the weight of the positive active material layer on the unit area of the positive plate, and the unit is g / cm < 2 >; r is the resistance of the positive plate at 25 DEG C, and the unit is omega.

Description

Positive electrode sheet, secondary battery and electrical device Technical field

[0001] This application belongs to the technical field of batteries. Specifically, it 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 hydropower, thermal power, wind power, and solar power plants, but also widely used in electric transportation such as electric bicycles, electric motorcycles, and electric vehicles, as well as in many fields such as military equipment and aerospace. With the development of current society, people's requirements for lithium-ion batteries are also getting higher and higher. 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, the rate tolerance boundary of conventional NCM system materials at low voltages is poor, which will affect the fast charging ability and actual available capacity of the battery.

[0003] Disclosure content

[0004] In view of the technical problems existing 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 ensure a long service life.

[0005] 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.

[0006] 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 of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, etc., and R′ includes one or more elements of N, F, S, Cl, etc.;

[0007] 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 the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W, A′ includes one or more elements selected from the group consisting of 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 the group consisting of B, Si, N, S, F, Cl, and Br;

[0008] The positive electrode sheet satisfies:

[0009] in:

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

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

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

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

[0014] Compared with the prior art, the positive electrode sheet of the first aspect of the present 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 has a poor rate tolerance margin at low SOC (state of charge, i.e., remaining capacity), and Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 has a poor rate tolerance margin at high SOC. By combining the two, the defects of the two systems can be compensated at the same time, and the rate tolerance margin at high and low SOC can be widened, thereby improving the fast charging capability. (2) By combining the positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ g With the positive electrode active material Li 1+x M 3n Mn 1-y A′y P 1- z E z O4 mixing can further make the battery have both high energy density and good cycle performance, thereby extending its service life; (3) Although the mechanism is not yet clear, the inventors have found that by controlling the content of Mn element in the positive electrode active material layer, the thickness and surface density of the positive electrode active material layer, and the positive electrode sheet resistance to meet the above range, the 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 the present application, Optionally, Among them, w (A′) is the mass fraction of A′ in the positive electrode active material layer, w (P) is the mass fraction of P in the positive electrode active material layer. By controlling it within the given range, we can further balance fast charging performance and long service life.

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

[0017] In some embodiments of the present 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, 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 the present application, 0.032≤T≤0.043, 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 achieved.

[0019] In some embodiments of the present application, 0.11≤d≤0.16, 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 achieved.

[0020] In some embodiments of the present application, 0<R≤1.2, optionally, 0<R≤1. By controlling R within a given range, the internal resistance of the electrode can be further reduced, and the fast charging performance and cycle performance can be improved.

[0021] In some embodiments of the present application, M1 is a Mn element.

[0022] In some embodiments of the present application, Optionally, Alternatively, 5 By controlling Within the given range, on the basis of improving the fast charging capability, we can further take into account higher energy density and better cycle performance to extend the service life.

[0023] In some embodiments of the present 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, further optionally 0.41 μm to 1.25 μm, further optionally 0.38 μm to 1.1 μm, and further optionally 0.47 μm to 0.91 μm.

[0024] In some embodiments of the present application, the specific surface area of ​​the second positive electrode active material is 9.2 m 2 / g~23.6m 2 / g, optional 10.5m 2 / g~19.6m 2 / g, and can be set to 12.0m 2 / g~16.2m 2 / g, 10.0m is also optional 2 / g~21.5m 2 / g, and can be selected as 10.9m 2 / g~17.6m 2 / g.

[0025] In some embodiments of the present application, Optionally, By controlling the positive electrode to meet the given conditions, it can be further ensured that the composite positive electrode has a better cycle life while having better power capability.

[0026] In some embodiments of the present 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 the present application, the specific surface area of ​​the first positive electrode active material is 0.3 m 2 / g~1.2m 2 / g, optional 0.5m 2 / g~0.9m 2 / g.

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

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

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

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

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

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

[0034] A second aspect of the present application provides a secondary battery, which includes: the positive electrode sheet of the first aspect of the present application.

[0035] The third aspect of the present application provides an electrical device, which includes: the positive electrode sheet of the first aspect of the present application, and / or the secondary battery described in the second aspect of the present application. DETAILED DESCRIPTION

[0036] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0037] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described in this application may 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, and a given range is defined by selecting a lower limit and / or an upper limit, and the selected lower limit and / or the rear upper limit define the boundaries of a particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range that is not clearly stated, and any lower limit can be combined with other lower limits to form a range that is not clearly stated, and similarly any upper limit can be combined with any other upper limit to form a range that is not clearly stated. In addition, each separately disclosed point or single numerical value itself can be combined with any other point or single numerical value as a lower limit or upper limit or with other lower limits or upper limits to form a range that is not clearly stated. For example, if a range of not more than 150 is listed for a particular parameter, it is also contemplated that 10 to 140 and 20 to 120, etc., satisfy a range of not more than 150. Furthermore, if the minimum range values ​​2.1 and 3.5 are listed, and if the maximum range values ​​4.9 and 6.3 are listed, then the following ranges are all contemplated: 2.1-6.3, 2.1-4.9, 3.5-6.3, and 3.5-4.9. In this application, unless otherwise indicated, a numerical range such as "10-50" is an abbreviation for any combination of real numbers between 10 and 50, where 10 and 50 are real numbers. For example, a numerical range of "20-30" indicates that all real numbers between "20-30" are listed herein, and "20-30" is merely an abbreviation for these numerical combinations.

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

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

[0041] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, which means that the method may include steps S1 and S2 performed sequentially, or may include steps S2 and S1 performed sequentially. For example, the method may further include step S3, which means that step S3 may be added to the method in any order, for example, the method may include steps S1, S2, and S3, or may include steps S1, S3, and S2, or may include steps S3, S1, and S2, etc.

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

[0043] Unless otherwise specified, the term "and / or" in this application simply describes an association between related objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this document generally indicates that the related objects are in an "or" relationship.

[0044] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and any variations thereof are intended to cover non-exclusive inclusions. Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0045] At present, fast charging performance and long service life have become important performance indicators for lithium batteries. Currently, a ternary layered cathode active material (such as NCM) is mostly used to prepare the cathode sheet. However, as the number of cycles increases and the discharge time prolongs for the cathode material of this system, problems such as an increase in battery internal resistance and an increase in electrode polarization will occur. As a result, the discharge voltage reaches the cut-off voltage in advance, and there is a tendency for a sharp drop in the discharge voltage at the end of the discharge curve during discharge, leading to an early end of discharge and affecting the actual available capacity of the battery. That is, the cathode material of this system has a poor rate tolerance boundary at low SOC, affecting the fast charging and cycling performance of the battery. In addition, although the ternary layered cathode active material (such as NCM) has a relatively high energy density, its cycle life and fast charging performance are not excellent.

[0046] In view of this, in the first aspect of the present application, a cathode sheet is provided. The cathode sheet includes a cathode active material layer, and the cathode active material layer includes a first cathode active material and a second cathode active material. The first cathode 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 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 cathode 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 cathode sheet satisfies:

[0047] where: 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. The dimension of “mass fraction” in this application is 1.

[0048] The inventors of the present application have discovered that the layered positive electrode active material system Li a Ni b Co c M 1d M 2e O f R′ g The rate tolerance margin is poor at low SOC, and 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 no more 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 Mn 1-y A′ y P 1-z E z The discharge platform of O4 at low voltage makes the overall discharge curve of the mixed composite positive electrode active material have a discharge platform near the end. When the battery discharges to this platform, since the battery voltage changes less with the capacity, it is equivalent to a certain degree of constant voltage discharge of the layered positive electrode active material, thereby alleviating the polarization effect in the previous discharge process at low voltage and improving the actual available capacity. In addition, the positive electrode active material system Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 is also limited by the problem of poor rate tolerance at high SOC. By combining it with the layered cathode active material system Li a Ni b Co c M 1d M 2e O f R′ g Mixed use can make up for the defects of the two systems at the same time, broaden the rate tolerance boundary at high and low SOC, thereby improving the fast charging capability and taking into account the cycle performance; In addition, the positive electrode active material Li a Ni b Coc M 1d M 2e O f R′ g The energy density is higher, and the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 has higher cycle performance and safety. By mixing the two, the electrode can be further made to have both higher energy density and better cycle performance, thus extending its service life. Moreover, the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z The lattice shrinkage rate of O4 during the charge and discharge process is relatively large. Mixing the positive electrode active materials of the two systems is also beneficial to further match the expansion of the battery negative electrode sheet and improve the long-term performance of the battery.

[0049] Furthermore, the inventors found in the process of exploration that 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 After O4 is mixed, by controlling the content of Mn element in the positive electrode active material layer, the thickness and surface density of the positive electrode active material layer, and the positive electrode sheet resistance to meet the above range, the fast charging capability, energy density and cycle performance can be guaranteed at the same time, and a fast charging positive electrode sheet with a good cycle life can be obtained. The reasons for this may include but are not limited to: the coating quality of the positive electrode active material will affect the 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, when the coating quality of the positive electrode active material layer is too low, the polarization of the electrode will be significantly improved.a Ni b Co c M 1d M 2e O f R′ g Medium blended 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, the polarization of the pole piece will increase to a greater extent than that of the mixed Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4's improvement effect; secondly, 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 infiltration of the electrolyte into the electrode sheet, 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.

[0050] 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 measured separately and then calculated. The mass of the positive electrode active material layer can be obtained by disassembling 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 operation can be performed: take about 0.4g of dry positive electrode sheet. (accurate to 0.0001g) or wet positive electrode 0.1g (accurate to 0.0001g) in a 30ml digestion tank, retain one digestion tank without sample as a blank sample, move the digestion tank containing the positive electrode sample into the fume hood and add 12ml of reverse aqua regia. When adding reverse aqua regia, add it along the inner wall of the digestion tank so that the residual sample on the inner wall is washed into the bottom of the tank, then install the top cover, insulation sleeve, gasket, microwave digestion device, nut in turn, tighten the nut with a wrench, then turn on the microwave digester, insert the fiber optic sensor in the microwave digester into the bottom of the digestion tank previously assembled with the sample, balance and place the digestion tank in the microwave digester, and start digestion (digestion program 6min heating to 120℃ and maintain for 8m in, heat to 160℃ for 5 minutes and hold for 8 minutes, heat to 180℃ for 5 minutes and hold for 5 minutes), cool to room temperature and take out, place the digestion tank in a fume hood, slowly unscrew the nut to release the air, remove the previously installed parts in turn, transfer the solution in the digestion tank to a 100ml volumetric flask through a funnel (filter paper is required), then rinse the digestion tank with ultrapure water, and transfer the rinse liquid to the volumetric flask, using 10ml of ultrapure water for each rinse, shake the solution in the 100ml volumetric flask, use a pipette to take 1ml of the shaken solution and add it to another 100ml volumetric flask, then add ultrapure water to make up the volume (the total solution reaches 100ml), and finally use ICP-OES to test the sample solution. Among them, when preparing reverse aqua regia, you can pour 1000ml of ultrapure water into a 2500ml glass bottle, and then add 750ml of concentrated nitric acid and 250ml of concentrated hydrochloric acid in turn, stir evenly and set aside. The concentrated nitric acid can be purchased from the market as a concentrated nitric acid solution with a mass fraction of 68%, and the concentrated hydrochloric acid can be purchased from the market as a concentrated hydrochloric acid with a mass fraction of 68%, or hydrogen chloride gas and ultrapure water can be added to ultrapure water with a mass ratio of 68% and 32% respectively. After complete dissolution, the required concentrated hydrochloric acid can be obtained.

[0051] In the present application, the coating mass T of the positive electrode active material layer can be tested by a weighing method, and specifically can be obtained by weighing the positive electrode active material layer within a fixed area (accurate to 0.0001 g).

[0052] 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 circular sheet with a diameter of 22 mm; (2) Place the prepared circular 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.

[0053] 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 position of the electrode sheet, transfer it under a vacuum transfer device or an inert gas 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-section 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 gas 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-section 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.

[0054] Furthermore, the inventors have further found through in-depth research that, on the basis of meeting the above conditions, the positive electrode sheet of this application can further control the element 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.

[0055] In some embodiments of this application, part of the first positive electrode active material can be Li a Ni b Co c M 1d M 2e O f R′ g , or it can all be 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 of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, etc., and R′ includes one or more elements of N, F, S, Cl. Optionally, 0.5 ≤ b < 1, 0 < c ≤ 0.5, 0 < d ≤ 0.5, so that the positive electrode active material Li a Ni b Coc M 1d M 2e O f R′ g Meeting the above-mentioned range conditions is more conducive to making the electrode and battery have higher energy density, good cycle performance and longer cycle life. The positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ g In the present invention, taking the nickel-cobalt-manganese ternary positive electrode active material (ie NCM) system as an example, increasing the nickel content can increase the volume energy density of the positive electrode material; increasing the manganese content can reduce the material cost, improve the safety and structural stability of the material, and improve the cycle performance, but too high a manganese content will destroy the layered structure of the material and reduce the specific capacity of the material; cobalt can stabilize the layered structure of the material and improve the cycle and rate performance of the material, but too high a cobalt content will lead to a decrease in the actual capacity. By making the nickel-cobalt-manganese content meet the above-mentioned range conditions, it is beneficial for the electrode and the battery to have a higher energy density, good rate performance and cycle performance. Optionally, M1 can be a Mn element, and the first positive electrode active material can be a positive electrode active material of the NCM system. In this case, its general formula can be Li a Ni b Co c Mn d M 2e O f R′ g , for example, it can be a nickel-cobalt-manganese ternary layered positive electrode active material.

[0056] In some embodiments of the present application, the second positive electrode active material may be partially Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4, or all 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≤1, 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. Doping at least one of the lithium site, manganese site and phosphorus site can help improve the performance of the positive electrode active material, for example, it can improve the interface performance, reduce the interface side reaction with the electrolyte, reduce the concentration of antisite defects, improve the material kinetic performance and gram capacity, etc. At the same time, by regulating the doping element at the manganese site, the particle morphology can also be improved and the compaction density can be increased. Specifically, the above-mentioned second positive electrode active material undergoes charge and discharge. The lattice volume change rate during the charging process is larger than that of 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 be detrimental to the transport of lithium ions. The manganese doping element A′ selected from the above elements helps to appropriately reduce the lattice change rate of the material during the lithium insertion and extraction process, improve the structural stability of the positive electrode material, reduce the dissolution of the manganese element, 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, thereby improving the material's cycle performance. The phosphorus doping element E selected from the above elements also helps to change the difficulty of the 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 material's capacity. If the value of x is too small, the lithium content of the entire core system will be reduced, affecting the specific capacity of the material. The y value will limit the total amount of all doping elements, affecting the manganese content in the system and the voltage platform of the material. The E element is doped in the position of phosphorus. Since the PO tetrahedron is relatively stable, a large z value will affect the stability of the material. When x, y and z are selected from the above ranges, the positive electrode active material can have better performance. In addition, the selection of the above doping elements and the values ​​of x, n, y, and z can also make Li 1+x M 3n Mn 1-y A′ y P 1-z E zO4 maintains electrical neutrality, and maintaining electrical neutrality can ensure that the defects and impurities in the positive electrode active material are as few as possible. Taking the positive electrode active material of the lithium manganese phosphate system as an example, if there is an excess of transition metal (such as manganese), since the structure of the material system itself is relatively stable, the excess transition metal is likely to precipitate in the form of a single substance, or form an impurity phase inside the lattice. Maintaining electrical neutrality can minimize such impurities. In addition, ensuring the electrical neutrality of the system can also produce lithium vacancies in the positive electrode active material in some cases, thereby making the kinetic performance of the positive electrode active material better. Compared with existing materials such as lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate that can be applied to high voltage systems, it is more conducive to obtaining better cycle performance and high temperature stability, as well as larger gram capacity and larger compaction density. It can be understood that in the "manganese position" doping described in this application, the manganese position only represents the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z The position of the manganese element or A' element in the O4 lattice does not necessarily mean that there is a manganese element in the manganese position. The manganese element on the manganese position can be partially or completely replaced by the A' element. For example, when the y value is 1, the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4 does not contain manganese. For example, in this case, the manganese position may include iron or iron and other doping elements.

[0057] In some embodiments of the present application, the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z In O4, E may include one or more elements selected from B, Si, N and S. By selecting the phosphorus-doped element E from a given range, it can further help to change the difficulty of changing the Mn-O bond length, 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.

[0058] In some embodiments of the present application, the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E zIn O4, A' can include one or more elements selected from Fe, Ti, V, and Mg. Alternatively, A' can be Fe; further alternatively, A' can be at least two elements selected from Fe, Ti, V, and Mg; and further alternatively, A' can be Fe and one or more elements selected from Ti, V, and Mg. By selecting the manganese-doped element A' within the given range, the structural stability, specific capacity, cycle performance, and rate performance of the positive electrode material can be further improved, resulting in a positive electrode sheet with both excellent cycle life and fast charging performance.

[0059] In some embodiments of the present application, the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z In O4, doping can be performed simultaneously at the manganese and phosphorus sites, which can not only effectively reduce the dissolution of manganese elements, thereby reducing the manganese ions migrating to the negative electrode, reducing the electrolyte consumption due to SEI film decomposition, and improving the cycle performance and safety performance, but also promote the adjustment of Mn-O bonds, reduce the lithium ion migration barrier, promote lithium ion migration, and improve the rate performance and fast charging capability. Alternatively, doping can be performed simultaneously at the lithium, manganese and phosphorus sites, thereby further obtaining significantly improved rate performance, improved cycle performance and / or high temperature stability.

[0060] 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 R′ g and the chemical formula of the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O4, unless otherwise specified, when a doping site has two or more elements, the numerical range of the stoichiometric number of the elements of the corresponding doping site in the chemical formula is not only limited to the stoichiometric number of each element as the site, but also limited to the sum of the stoichiometric numbers of the elements as the site. For example, 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′ is two or more elements A1′, A2′…A n', A1', A2'...A n 'The respective stoichiometric numbers y1, y2...y n Each of them must fall within the numerical range of y specified in this application, and y1, y2...y n Similarly, for the case where M3 or E is two or more elements, the numerical ranges of the stoichiometric numbers of M3 and E defined in this application also have the above meanings.

[0061] In some embodiments of the present application, The value range of 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 within any range of the above values. Optionally, The value range of can be 0.07~0.1, then 0.07~0.092, then 0.07~0.9, and then 0.07~0.8. If the value of is within the given range, a fast-charging positive electrode sheet with a better cycle life can be further obtained.

[0062] In some embodiments of the present application, w (A′) is the mass fraction of A′ in the positive electrode active material layer, w (P) is the mass fraction of phosphorus element P in the positive electrode active material layer, for example, The value of 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. 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 mixing is beneficial to improve the power capacity at lower voltage and the cycle performance of the composite positive electrode, and as the mixing ratio of the two changes, the power capacity at low voltage and high voltage and the cycle performance of the composite positive electrode will also change. For example, when Li 1+x M 3n Mn 1-y A′y P 1- z E z When the O4 mixing ratio is too high, it will affect the power capacity at higher voltages, thereby deteriorating the power capacity of the composite positive electrode. Controlling within the given range is beneficial to making 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, thus ensuring that the composite positive electrode power capacity and cycle performance are better, and can better balance fast charging performance and long service life. By Controlled within the given range, Li can be further optimized a Ni b Co c M 1d M 2e O f R′ g He Li 1+x M 3n Mn 1-y A′ y P 1-z E z The mixing ratio of O4 is adjusted to obtain a fast-charging positive electrode sheet with a better cycle life.

[0063] In some embodiments of the present application, the mass fraction of the A' element in the positive electrode active material layer satisfies: 0.01≤w (A′) ≤0.05, for example, w (A′) The value of can be 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, etc., or within any range of the above arbitrary values. In the second positive electrode active material, increasing the content of A' element helps to improve the 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 take into account both the cycle performance and the high energy density on the basis of improving the fast charging performance of the positive electrode sheet, thereby extending the service life.

[0064] In some embodiments of the present application, the second positive electrode active material may include a lithium manganese phosphate system, a lithium iron phosphate system, a lithium manganese iron phosphate system, and the like, all of which conform to the above general formula Li1+x M 3n Mn 1-y A′ 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 meets 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 A′ y P 1-z E z O4, that is, it can be lithium manganese phosphate doped with at least manganese position, wherein, in the present application, by modifying the lithium manganese phosphate, it is possible to achieve significantly reduced manganese position element dissolution and reduced lattice change rate, which is used in secondary batteries, and is more conducive to improving the battery's cycle performance, rate performance, safety performance and increasing the battery's capacity. For example, by doping specific elements in specific amounts at the lithium position, manganese position, and phosphorus position of the compound LiMnPO4, it is possible to obtain improved rate performance, while reducing the dissolution of Mn and Mn position doping elements, obtaining improved cycle performance and / or high temperature stability, and the gram capacity and compaction density of the positive electrode active material can also be improved. As a specific example, Li 1+x Mn 1-y A′ y P 1-z E z O4 may include Li 1+x Mn 1-y Fe y P 1-z E z O4, compared with lithium iron phosphate, lithium manganese iron phosphate has a higher voltage platform and a higher energy density when the specific capacity is the same; (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 A′ y P 1-z E z O4, for the second positive electrode active material of the lithium manganese phosphate system, considering that the y value will limit the total amount of all doping elements, if y is too small, that is, the doping amount is too little, 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 platform of the material. The value range of y can be selected from 0.001 to 0.500, and then from 0.25 to 0.5. It should be noted that the chemical formula Li 1+x Mn 1- y A′ y P1-z E z O4 and Li 1+x M 3n Mn 1-y A′ y P 1-z E z In O4, the stoichiometric numbers of elements at the same site can be the same or different, but they all satisfy the chemical formula Li 1+x M 3n Mn 1-y A′ y P 1-z E z The numerical range defined for the stoichiometric number of each element in O4.

[0065] 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 A′ y P 1-z E z Alternatively, the second positive electrode active material may include only the chemical formula Li 1+x Mn 1-y A′ y P 1-z E z Alternatively, A′ may include Fe element, for example, may be only Fe element.

[0066] In some embodiments of the present application, the weight T (unit: g / cm2) of the positive electrode active material layer per unit area of ​​the positive electrode sheet is 2 ) satisfies: 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-mentioned values. The coating quality of the positive electrode active material layer not only affects the polarization of the electrode, but also affects the energy density of the electrode. Under the premise of satisfying the relationship between the content of the A′ element 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, the present application further controls the surface density T of the positive electrode active material layer within the given range, thereby further obtaining improved fast charging performance and cycle life, as well as higher energy density and extended service life. Optionally, 0.035≤T≤0.039, further controlling T within the given range can further enable the positive electrode sheet to have both good fast charging capability and long service life.

[0067] 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, it is possible to further simultaneously obtain improved fast charging performance and cycle life, as well as a higher energy density, and extend the service life. Optionally, 0.12 ≤ d ≤ 0.14. Further controlling d within the given range can further enable the positive electrode sheet to have both good fast charging ability and long service life.

[0068] 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 is further beneficial to enable the electrode sheet to have good fast charging performance and cycling performance. Optionally, 0 < R ≤ 1. By further controlling the value range of R within the given range, it is possible to further reduce the internal resistance of the electrode sheet and improve the fast charging performance and cycling performance.

[0069] In some embodiments of the present application, the mass fractions of Mn element and A' element in the positive electrode active material layer may 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 high 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 included 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 The value of is within the given range, so that the second positive electrode active material has an appropriate A' element content range, thereby further taking into account higher energy density and better cycle performance on the basis of improving fast charging capability, thereby extending service life. Alternatively, This can further achieve high energy density, as well as improved fast charging performance and long service life.

[0070] As a specific example, the first positive electrode active material may be a positive electrode active material Li a Ni b Co c Mn d M 2e O f R′ g , such as 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), such as Li 1+x Mn 1-y Fe y P 1-z E z O4, at this time The value range of can be 3 to 20, optionally 4 to 18, and further optionally 5 to 17; further, The value range of can be 0.27~1.63, and can be selected as 0.72~1.26; further, w (A′) The value of can be 0.01 to 0.05. In the present application, by making the positive electrode sheet meet the given conditions, the improved fast charging performance, cycle performance and long service life can be further obtained.

[0071] In some embodiments of the present application, the positive electrode sheet may simultaneously meet the following two conditions: Optionally, The changes in the content of Mn and A' in the positive electrode active material layer, especially in the second positive electrode active material, will directly or indirectly affect the fast charging capability and cycle life of the composite positive electrode. The change in the value of The value range of will also change accordingly. The inventors found in the exploration process that when and When the values ​​of satisfy the given range at the same time, it can further ensure that the composite positive electrode has a better power capability and a better cycle life.

[0072] In some embodiments of the present 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, etc., or within any range of the above values. The Dv50 of the first positive electrode active material refers to the particle size corresponding to the cumulative volume distribution percentage of the first positive electrode active material reaching 50%. In the present application, the Dv50 particle size of the first positive electrode active material can be measured by laser diffraction particle size analysis, for example, with reference to standard GB / T 19077-2016, using a laser particle size analyzer (such as Malvern Master Size 3000) for measurement. In this application, by controlling the Dv50 particle size of the first positive electrode active material within the given range, it is not only beneficial to prevent it from breaking or pulverizing during the charge and discharge process, thereby reducing capacity loss, but also can shorten the diffusion path of active ions and increase the conduction rate of electrons, which is beneficial to improving cycle performance; at the same time, it can also make the active material have suitable active sites, reduce or avoid the fact that there are more active sites when the particle size is too small, which increases the side reactions of the material during the cycle and has a greater negative impact on the cycle performance, and that there are fewer active sites when the particle size is too large, which has a greater negative impact on the power performance. Optionally, the Dv50 particle size of the first positive electrode active material can be 3.5μm to 4.9μm, which can further take into account high energy density, good power performance and cycle performance, and improve fast charging capability and service life.

[0073] In some embodiments of the present application, the Dv50 particle size of the second positive electrode active material may 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 within any range of the above values. The Dv50 of the second positive electrode active material refers to the particle size corresponding to the cumulative volume distribution percentage of the second positive electrode active material reaching 50%. In the present application, the Dv50 particle size of the second positive electrode active material can be measured by laser diffraction particle size analysis, for example, with reference to standard GB / T 19077-2016, using a laser particle size analyzer (such as Malvern Master Size 3000) for measurement. In this application, by controlling the Dv50 particle size of the second positive electrode active material within the given range, it is not only beneficial to prevent it from breaking or pulverizing during the charge and discharge process, thereby reducing capacity loss, but also can shorten the diffusion path of active ions and increase the conduction rate of electrons, which is beneficial to improving cycle performance. At the same time, it can also make the active material have suitable active sites, while taking into account both cycle performance and power performance; and, controlling the Dv50 particle size of the second positive electrode active material within the given range is also beneficial to achieve the expected compaction density with 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 0.5μm to 0.9μm, thereby further taking into account high energy density, good power performance and cycle performance, and improving fast charging capability and service life.

[0074] In some embodiments of the present application, the specific surface area of ​​the first positive electrode active material may be 0.3 m 2 / g~1.2m 2 / g, for example, 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, etc., or within any range of the above values; Optionally, the specific surface area of ​​the first positive electrode active material can be 0.5m 2 / g~0.9m 2 / g. Further, the specific surface area of ​​the second positive electrode active material can be 9.2m 2 / g~23.6m 2 / g, for example, 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, etc., or within any range of the above values; Optionally, the specific surface area of ​​the second positive electrode active material is 10.5m 2 / g~19.6m 2 / g, and can be set to 12.0m 2 / g~16.2m 2 / g, 10.0m is also optional 2 / g~21.5m 2 / g, and can be selected as 10.9m 2 / g~17.6m 2 / g. In the present application, the specific surface areas of the first and second positive electrode active materials can be respectively measured by conventional methods in the field, such as nitrogen physical adsorption method. The increase in specific surface area helps to increase the active sites of the positive electrode active material, so that the material has better power performance, but these increased active sites will also increase the side reactions of the positive electrode active material during the cycle, thereby causing the material cycle performance to decay. In the present application, by controlling the specific surface areas of the first positive electrode active material and the second positive electrode active material within the given range, better power performance and cycle life can be further obtained, and the fast charging capability and service life can be improved.

[0075] As a specific example, when the positive electrode active material layer satisfy When the second positive electrode active material has a Dv50 particle size of 0.21 μm to 1.53 μm and a specific surface area of ​​9.2 m 2 / g~23.6m 2 / g; further, when satisfy When the Dv50 particle size of the second positive electrode active material can be 0.38 μm to 1.10 μm, and can be 0.47 μm to 0.91 μm, the specific surface area of ​​the second positive electrode active material can be 10.5 m 2 / g~19.9m 2 / g, optional 12.0m 2 / g~16.2m 2 / g; further, when satisfy When the Dv50 particle size of the second positive electrode active material can be 0.32 μm to 1.40 μm, and can be 0.41 μm to 1.25 μm, the specific surface area of ​​the second positive electrode active material can be 10.0 m 2 / g~21.5m 2 / g, optional 10.9m 2 / g~17.6m 2 / g. The inventors also found in the exploration process that the changes in the Dv50 particle size and specific surface area of ​​the second positive electrode active material will affect the power performance and cycle life of the material, and different The corresponding optimal Dv50 particle size and specific surface area ranges are also different. The Dv50 particle size and specific surface area of ​​the second positive electrode active material meet the above-given range conditions, which can further enable the composite positive electrode to have a better power capability and a better cycle life.

[0076] In some embodiments of the present application, a first coating layer may be provided on the surface of the first positive electrode active material. Optionally, the first coating layer may include one or more elements selected from the group consisting of Ti, Al, B, Nb, Zr, Si, and W. Providing a coating layer on the surface of the positive electrode active material can not only prevent the positive electrode active material from contacting the electrolyte, thereby reducing the side reactions between the positive electrode active material and the electrolyte, but also improve the stability of the structure of the positive electrode active material, thereby improving the cycle stability and safety of the material. In addition, the above elements in the first coating layer can be provided in the form of oxides (such as Al2O3, ZrO2, TiO2, Nb2O3, etc.) or in the form of lithium compounds, etc. Including the above-mentioned element range in the first coating layer can improve the surface ionic conductivity of the material, improve the material rate performance and specific capacity, stabilize the material structure, avoid direct contact between the material and the electrolyte, and improve the cycle performance.

[0077] In some embodiments of the present 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, etc., or in any range of the above arbitrary values. The inventors found that when the thickness of the first coating layer is too thin, the possibility of its cracking / deep damage during the use of the positive electrode active material will increase, resulting in a significant reduction in the effect of improving and protecting the performance of the first positive electrode active material; when the thickness of the first coating layer is too thick, lithium ions require a longer transmission path to reach the active material system from the electrolyte, which has a greater impact on the performance of the active material. In addition, when the coating layer is sintered, the coating material will react with the lithium in the internal material, resulting in a reduction in the available active lithium in the material and a corresponding reduction in the specific capacity of the material. In this application, by controlling the thickness of the first coating layer within the above given range, the above problems can be effectively avoided or reduced, the rate performance of the first positive electrode active material can be effectively improved, and the surface structure of the material can be stabilized. At the same time, based on the Dv50 particle size of the first positive electrode active material, by controlling the thickness of the first coating layer within a given range, it is also beneficial to further ensure the high energy density of the composite positive electrode.

[0078] In some embodiments of the present application, a second coating layer may be provided on the surface of the second positive electrode active material. The provision of the second coating layer can not only prevent the second positive electrode active material from contacting the electrolyte, thereby reducing the side reaction between the second positive electrode active material and the electrolyte, but also prevent or inhibit the dissolution of transition metals or doping elements in the second positive electrode active material, while improving its structural stability, thereby improving 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. Among them, metal ions are difficult to migrate in pyrophosphate, and 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 can be selected as a crystalline pyrophosphate, which has a stable structure and can be used as a coating layer material to effectively inhibit the dissolution of transition metals in the active material and improve the cycle performance. Phosphate coating can improve the ion transport properties of the positive electrode material, which is beneficial for promoting the transmission of lithium ions. Furthermore, the phosphate can be a crystalline phosphate. Crystalline phosphate and crystalline pyrophosphate have a high lattice matching degree, good stability and excellent lithium ion conductivity. Using them to coat the second positive electrode active material can improve the stability of the positive electrode active material and effectively reduce the interfacial side reactions of the electrolyte, thereby improving the high-temperature cycling and storage performance of the battery. Carbon coating can effectively improve the conductivity and desolvation ability of the positive electrode active material. Carbon materials have good electronic conductivity. When used in batteries, electrochemical reactions occur, which require the participation of electrons. In order to increase electron transmission between particles and electron transmission at different positions of particles, carbon with excellent conductive properties can be used to coat the positive electrode active material. It can be understood that when the second coating layer includes pyrophosphate, phosphate and carbon at the same time, 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 in sequence 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 in sequence on the surface of the second positive electrode active material, or a composite coating layer of pyrophosphate and phosphate can be first formed 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.

[0079] In some embodiments of the present application, the thickness of the second coating layer may be 10 nm to 50 nm. For example, it may be 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 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 the transition metal or doping element in the second positive electrode active material and reduce the lattice change rate of the second positive electrode active material, but also avoid the coating thickness being too large to affect the migration of lithium ions and affect the battery energy density, thereby further improving the battery's kinetic performance, cycle performance and safety without sacrificing the gram capacity of the second positive electrode active material.

[0080] 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 can effectively inhibit the dissolution of transition metals in the second positive electrode active material, thereby improving the cycle performance. The crystalline phosphate as the second sub-coating layer has a high lattice match with the crystalline pyrophosphate in the first sub-coating layer, is more stable than pyrophosphate, and has excellent lithium ion conductivity, which is beneficial for improving the stability of the positive electrode active material and reducing the 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 conductive properties and desolvation ability of the positive electrode active material. Further, the thickness of the first sub-coating layer can be 1nm to 10nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, etc., or within any range of the above-mentioned arbitrary values. When the thickness of the first sub-coating layer is within the given range, it can avoid the adverse effects on the kinetic properties of the positive electrode active material that may be caused when it is too thick, and can avoid the problem that it may not effectively hinder the migration of transition metal ions when it is too thin; the thickness of the second sub-coating layer can be 2nm to 15nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, etc., or within any range of the above-mentioned arbitrary values. The thickness of the second sub-coating layer is too large and may cause Affects the overall platform voltage of the positive electrode active material. When the thickness of the second sub-coating layer is within the given range, its surface structure is stable, the side reaction with the electrolyte is small, and the interface side reaction can be effectively reduced, thereby improving 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 within any range of any of the above values. When the thickness of the third sub-coating layer is within the given range, it can improve the electrical conductivity of the positive electrode active material and the compaction density of the positive electrode sheet, while avoiding the problem of the sub-coating layer containing amorphous carbon affecting the compaction density of the sheet due to excessive coating thickness.

[0081] Among them, in the present application, the thickness test of each coating layer can be carried out by FIB, and the specific method may include the following steps: randomly selecting a single particle from the positive electrode active material powder to be tested, cutting 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 performing TEM testing on the thin slice to measure the thickness of the coating layer, measuring 3 to 5 positions, and taking the average value.

[0082] A second aspect of the present application provides a secondary battery, which includes: the positive electrode sheet of the first aspect of the present application.

[0083] In a secondary battery, it usually includes a shell assembly, a positive electrode sheet, a negative electrode sheet, a diaphragm, and an electrolyte. The positive electrode sheet, the negative electrode sheet, the diaphragm, and the electrolyte are located in a receiving cavity formed by the shell assembly. According to the type of battery, the shell assembly can be an aluminum-plastic film or a metal shell assembly, etc. The metal shell assembly can include a square shell assembly and a cylindrical shell assembly. When the shell assembly is a metal shell assembly, it usually includes a shell with an opening on at least one side and a cover for sealing the opening. Regardless of the type of battery, as long as its positive electrode sheet includes the positive electrode sheet of the first aspect of the present application, it can be understood to be included in the technical scope of the battery of the fourth aspect of the present application. In addition to the characteristics such as the compaction density of the active material and active material layer of the aforementioned positive electrode sheet, other structural features or material selection of the positive electrode sheet, as well as the selection of the negative electrode sheet, diaphragm and electrolyte can adopt conventional selections in the field, and those skilled in the art can flexibly select according to actual needs.

[0084] In some embodiments of the present application, the secondary battery can be either a laminated battery or a wound battery. The wound battery can be either a square battery or a cylindrical battery. Optionally, the battery can be a cylindrical battery. Depending on the battery type, the positive electrode sheet, the negative electrode sheet, and the separator can be stacked to form a laminate unit, or can be stacked and then wound to form a wound body.

[0085] In some embodiments of the present application, the battery may be a single cell or a battery module assembled from cells. A battery module may include multiple cells, the specific number of which may be adjusted based on the application and capacity of the battery module. Furthermore, the battery module may also include a packaging assembly having a storage space, which may include a bottom plate, side plates, and a cover plate.

[0086] In some embodiments of the present application, the above-mentioned battery modules may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0087] In addition, the present application also provides an electrical device, which includes: the positive electrode sheet of the first aspect of the present application, and / or the secondary battery of the second aspect of the present application.

[0088] The secondary battery, such as a battery cell, battery module or battery pack, can be used as both a power source and an energy storage unit for the electrical device. The electrical device may include, but is not limited to, a mobile device (e.g., a mobile phone, a laptop computer), an electric vehicle (e.g., 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, a satellite, and an energy storage system. As a specific example, the electrical device may be a vehicle.

[0089] The electrical device can select the specific type of battery according to its usage requirements, such as battery cells, battery modules or battery packs.

[0090] As an example, the electric device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the electric device's requirements for high power and high energy density of the battery, a battery pack or battery module may be used.

[0091] As another example, the electrical device may be a mobile phone, a tablet computer, or a laptop computer. The electrical device is generally required to be lightweight and thin, and may use a battery cell as a power source.

[0092] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0093] Preparation and testing methods of secondary batteries:

[0094] 1. Soft-pack laminated battery:

[0095] ① Preparation of positive electrode sheet:

[0096] The positive electrode active material, polyvinylidene fluoride (PVDF), and conductive carbon are added to a certain amount of N-methylpyrrolidone (NMP) with a mass ratio of positive electrode active material: polyvinylidene fluoride: conductive carbon of 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 on aluminum foil and dried to form a positive electrode sheet.

[0097] ② Preparation of negative electrode sheet:

[0098] Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon were added to a certain amount of deionized water. The mass ratio of graphite: sodium carboxymethyl cellulose: styrene-butadiene rubber: conductive carbon was 90:2:3:5. The mixture was stirred to form a uniform slurry with a viscosity controlled at 3000-10000 mPa·s. The slurry was then coated on copper foil and dried to form a negative electrode sheet.

[0099] ③ Preparation of soft-pack laminated batteries:

[0100] The prepared positive electrode sheet, negative electrode sheet and separator (polyethylene (PE) porous polymer film) are made into corresponding battery cells according to a Z-shaped stacking structure, and the battery cells are vacuum dried at 90°C for 12 hours, and then the positive and negative electrode tabs are ultrasonically welded. The positive electrode uses an aluminum tab and the negative electrode uses a nickel tab. The positive and negative electrode tabs are located on the same side of the battery cell. The battery cell after the tab welding is placed in an aluminum-plastic film of appropriate size for top-side packaging. The conventional packaging temperature is 145°C, and the electrolyte is injected (the electrolyte is 1 mol / L LiPF6 / (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1) + 5wt.% fluoroethylene carbonate (FEC)), let it stand, form, age, exhaust, seal, and capacity test to obtain the prepared soft-pack laminated battery.

[0101] 2. Carry out cycle test on the prepared soft-pack laminated battery at 25°C:

[0102] The prepared soft-pack laminated battery was charged to 4.4V at 0.5C0 at 2.5-4.4V in a constant temperature environment of 25°C, then charged at a constant voltage at 4.4V to a current ≤ 0.05C0, allowed to stand for 5 minutes, and then discharged to 2.5V at 1C0. The capacity was recorded as C n (n=1,2,3……), repeat the above operation, the capacity retention rate is calculated according to C n / C3 ratio calculation, when C n When / C3×100%=80%, the corresponding number of cycles is extracted as the evaluation index of the cycle capacity;

[0103] 3. Positive electrode sheet resistance test:

[0104] The diaphragm resistance is tested using a BER1300 diaphragm resistance meter. The test steps are as follows: (a) prepare the electrode into a disc with a diameter of 22 mm; (b) place the prepared disc on the test platform of the BER1300 instrument; (c) adjust the machine test pressure to 0.4 T, the test temperature to 25°C, and the test time to 10 s, and then start the test. The obtained resistance value is the diaphragm resistance.

[0105] 4. 10%~80% SOC charging time experiment:

[0106] First, the capacity of the soft-pack laminated battery is tested. The process is as follows: 0.33C constant current charging to the full charge voltage V1 is switched to constant voltage charging. When the charging current is reduced to 0.05C, the constant voltage charging is ended. Then 0.33C is discharged to the full discharge voltage V2. This process is repeated 3 times, and the third capacity result is taken as the standard. At the same time, the third result can be used to calculate the positive electrode gram capacity.

[0107] The soft-pack laminated battery was tested at different rates (C1 <C2<C3<C4<……<C n ) Charging test, during the test, the charging rate needs to be from small to large, and the full voltage of the soft-pack laminated battery and the negative electrode voltage of the soft-pack laminated battery need to be monitored simultaneously during the charging process. The detailed process is as follows: the soft-pack laminated battery is charged to the full charge voltage V1 or the negative electrode voltage is 0V according to C1, the battery SOC value at the end of charging is extracted, and then 0.33C is discharged to the full discharge voltage V2. The above process can be repeated to obtain the SOC value at the end of charging at different rates. The SOC-rate at the end of charging is made into a scatter plot, and the relationship between the SOC and the rate at the end of charging is fitted. 20%, 30%, 40%, 50%, 60%, 70%, and 80% are substituted into the relationship to obtain the corresponding rate (C 20％ 、C 30％ 、C 40％ 、C 50％ 、C 60％ 、C 70％ 、C 80％ ) can be used to calculate the 10% to 80% SOC charging time, 10% to 80% SOC charging time = (60 / C 20％ +60 / C 30％ +……+60 / C 80％ )×10%.

[0108] Example 1

[0109] In soft-pack laminated batteries:

[0110] (i) Positive electrode sheet: The number of positive electrode sheets is 15; the thickness of a single-layer positive electrode sheet is 0.13 mm; the weight of the positive electrode active material layer per unit area of ​​the positive electrode sheet is 0.038 g / cm 2 The first positive electrode active material is NCM523, the Dv50 particle size of the first positive electrode active material is 4.2 μm, and the specific surface area of ​​the first positive electrode active material is 0.5 m 2 / g; the second positive electrode active material is LiMn 0.6 Fe 0.4 PO4, the Dv50 particle size of the second positive electrode active material is 0.8 μm, and the specific surface area of ​​the second positive electrode active material is 13.3 m 2 / g; the positive electrode meets the following requirements: A′ is The electrode resistance is 0.7Ω.

[0111] (ii) Negative electrode sheet: The number of negative electrode sheet layers is 16; the thickness of a single-layer negative electrode sheet is 0.13 mm; the weight of the negative electrode active material layer per unit area of ​​the negative electrode sheet is 0.012 to 0.030 g / cm 2 .

[0112] (iii) Diaphragm: The number of diaphragm layers is 16; the thickness of a single-layer diaphragm is 0.012 mm.

[0113] (iv) The inner thickness of the battery case is 6.1 mm.

[0114] (v) The filling coefficient of the secondary battery is 2.84 g / Ah.

[0115] Examples 2 to 15 and Comparative Examples 1 to 3

[0116] The difference between Examples 1 to 9 and Comparative Examples 1 to 3 and Example 1 is that: The value range of is different, and this difference is achieved by changing the blending ratio of the first positive electrode active material and the second positive electrode active material, as shown in Table 1 for details.

[0117] The difference between Examples 10 to 15 and Example 1 is that the types of the second positive electrode active materials are different, as shown in Table 1 for details.

[0118] The batteries assembled in Examples 1 to 15 and Comparative Examples 1 to 3 were tested. The test results are shown in Table 1.

[0119] Table 1 Differences between Examples 1 to 15 and Comparative Examples 1 to 3 and related test results

[0120] Results and Conclusions:

[0121] In combination with the above embodiments and comparative examples, it can be seen that the battery design scheme of the present application can improve the fast charging performance and cycle performance of the battery. Specifically, in combination with Examples 1 to 9 and Comparative Examples 1 to 3, it can be seen that when the first positive electrode active material and the second positive electrode active material are determined, as the mixing ratio of the two changes, the resistance of the positive electrode sheet, the content of the Mn element in the electrode sheet, and the relative amount of the Mn element and the A' element (Fe element in the above embodiment), and The value of will change accordingly; Combining Example 1 and Examples 10 to 15, it can be seen that the change in the type of the second positive electrode active material will also affect the resistance of the positive electrode sheet, the content of the Mn element in the electrode sheet, and the relative amount of the Mn element and the A' element (Fe element in the above embodiment), as well as But in general, When the value range of is between 0.002 and 0.2, the fast charging performance and cycle performance of the battery are relatively good, and it can be selected from 0.03 to 0.085; on this basis, the relative amount of Mn and Fe in the positive electrode sheet The value of can be selected from 3 to 20, and further selected from 5 to 17.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A positive electrode sheet, in, The positive electrode sheet includes a positive electrode active material layer, wherein 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 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,M 1 is Mn element and / or Al element, M 2 It includes one or more elements selected from the group consisting of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and R′ includes one or more elements selected from the group consisting of N, F, S, and Cl; The second positive electrode active material includes Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 , where -0.100≤x≤0.100, 0≤n≤1.1, 0.001≤y≤0.500, 0≤z≤0.100, M 3 includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo and W, A′ includes one or more elements selected from the group consisting of 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 the group consisting of B, Si, N, S, F, Cl and Br; The positive electrode sheet satisfies: in: 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.

2. The positive electrode sheet according to claim 1, in, Optionally, Among them, w (A′) is the mass fraction of A′ in the positive electrode active material layer, w (P) is the mass fraction of P in the positive electrode active material layer.

3. The positive electrode sheet according to claim 1 or 2, in, 0.01≤w (A′) ≤0.05。 4. The positive electrode sheet according to any one of claims 1 to 3, in, 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 O 4 ; (ii) 0.001≤y≤0.500, 0.9≤n≤1.1, and the second positive electrode active material is Li 1+x M 3n Mn 1-y A′ y P 1- z E z O 4 , Optionally, the second positive electrode active material is: (ii) Li 1+x Mn 1-y A′ y P 1-z E z O 4 .

5. The positive electrode sheet according to any one of claims 1 to 4, in, 0.032≤T≤0.043, optionally, 0.035≤T≤0.

039.

6. The positive electrode sheet according to any one of claims 1 to 5, in, 0.11≤d≤0.16, optionally, 0.12≤d≤0.

14.

7. The positive electrode sheet according to any one of claims 1 to 6, in, 0<R≤1.2, optionally, 0<R≤1.

8. The positive electrode sheet according to any one of claims 1 to 7, in, M 1 It is the Mn element.

9. The positive electrode sheet according to any one of claims 1 to 8, in, At least one of the following conditions is met: Optionally, Alternatively, 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, further optionally 0.41 μm to 1.25 μm, further optionally 0.38 μm to 1.1 μm, and further optionally 0.47 μm to 0.91 μm; The specific surface area of ​​the second positive electrode active material is 9.2 m 2 / g~23.6m 2 / g, optional 10.5m 2 / g~19.6m 2 / g, and can be selected as 12.0m 2 / g~16.2m 2 / g, 10.0m can also be selected 2 / g~21.5m 2 / g, and can be selected as 10.9m 2 / g~17.6m 2 / g.

10. The positive electrode sheet according to claim 9, in, Optionally, 11. The positive electrode sheet according to any one of claims 1 to 10, in, 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.

12. The positive electrode sheet according to any one of claims 1 to 11, in, The specific surface area of ​​the first positive electrode active material is 0.3 m 2 / g~1.2m 2 / g, optional 0.5m 2 / g~0.9m 2 / g.

13. The positive electrode sheet according to any one of claims 1 to 12, in, A first coating layer is provided on the surface of the first positive electrode active material. Optionally, the first coating layer includes one or more elements selected from the group consisting of Ti, Al, B, Nb, Zr, Si and W.

14. The positive electrode sheet according to claim 13, in, The thickness of the first coating layer is 20 nm to 150 nm.

15. The positive electrode sheet according to any one of claims 1 to 14, in, A second coating layer is provided on the surface of the second positive electrode active material. Optionally, the second coating layer includes at least one of pyrophosphate, phosphate and carbon.

16. The positive electrode sheet according to claim 15, in, The thickness of the second coating layer is 10 nm to 50 nm.

17. The positive electrode sheet according to any one of claims 1 to 16, in, In the second positive electrode active material, E includes one or more elements selected from the group consisting of B, Si, N and S.

18. The positive electrode sheet according to any one of claims 1 to 17, in, In the second positive electrode active material, A′ includes one or more elements selected from the group consisting of Fe, Ti, V, Ni, Co and Mg.

19. A secondary battery, in, A positive electrode sheet comprising any one of claims 1 to 18.

20. An electrical device, in, A secondary battery comprising the positive electrode sheet according to any one of claims 1 to 18 and / or the secondary battery according to claim 19.

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