Positive electrode plate, secondary battery and power consumption device

Abstract

This application discloses a positive electrode plate, a secondary battery, and a power consumption device. Here, the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material includes Li a Ni b Co c M 1d M 2e O f R´ g and satisfies 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 an Mn element and / or an Al element. The second positive electrode active material includes Li 1+x M 3n Mn 1-y A´ y P 1-z E z O4 and satisfies -0.100 ≦ x ≦ 0.100, 0 ≦ n ≦ 1.1, 0.001 ≦ y ≦ 1, 0 ≦ z ≦ 0.100. A´ includes one or more elements among Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge. The positive electrode plate satisfies JPEG2025535338000041.jpg14170, where n (A´) , n (Ni) , n (Mn) are the molar amounts of A´, Ni, and Mn in the positive electrode plate in order, with the unit being mol. R is the resistance of the positive electrode plate at 25°C, with the unit being Ω.

Description

[Technical Field]

[0001] The present application relates to the field of battery technology, and more particularly to positive electrode plates, secondary batteries and power consuming devices. [Background technology]

[0002] Lithium-ion batteries are environmentally friendly, high-energy, and low-carbon. They are widely used in energy storage systems for hydroelectric, thermal, wind, and solar power plants, as well as in electric transportation tools such as electric bicycles, electric motorcycles, and electric vehicles, as well as in military equipment and aerospace. With the development of society, people's demands for lithium-ion batteries are increasing, and fast-charging and cycling performance have become important performance indicators for lithium batteries. Currently, ternary layered positive electrode materials, such as nickel-cobalt-manganese (NCM)-based materials, are often used as the positive electrode material for lithium-ion batteries. However, conventional NCM-based materials have relatively poor rate-resistance limits at low voltages, which impact the fast-charging capability and actual usable capacity of the battery. Summary of the Invention [Problem to be solved by the invention]

[0003] In view of the technical problems existing in the background art, the present application provides a positive electrode plate that aims to expand the rate tolerance boundary at high and low voltage points of a positive electrode active material, improve fast charging capability, and at the same time ensure cycle performance.

[0004] In order to achieve the above object, a first aspect of the present application provides a positive electrode plate, wherein the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer including a first positive electrode active material and a second positive electrode active material; The first positive electrode active material is Li a Ni b Co c M 1d M 2e O f R´ gcomprising, 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, and f + g ≦ 3; M1 is an Mn element and / or an Al element; M2 comprises one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb; R´ comprises one or more elements selected from N, F, S, and Cl. The second positive electrode active material is Li 1+x M 3n Mn 1-y A´ y P 1-z E z comprises LiM 1+x A´ y P 1-z EO4, where -0.100 ≦ x ≦ 0.100, 0 ≦ n ≦ 1.1, 0.001 ≦ y ≦ 1, 0 ≦ z ≦ 0.100; M3 comprises one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; A´ comprises one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge; E comprises one or more elements selected from B, Si, N, S, F, Cl, and Br. The positive electrode plate

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[0005] Compared with the prior art, the positive electrode plate of the first aspect of the present application has at least the following beneficial effects. (1) The Li a Ni b Co c M 1d M 2e O f R´ g positive electrode active material system has a relatively poor rate resistance boundary at low SOC (state of charge, i.e., remaining amount) locations, and Li1+x M 3n Mn 1-y A´ y P 1-z E z O4 has a relatively poor rate tolerance boundary at high SOC. By using both in combination, the defects of the two systems can be simultaneously compensated for, widening the rate tolerance boundary at high and low SOC, thereby improving the fast charging capability. (2) Positive electrode active material Li a Ni b Co c M 1d M 2e O f R´ g and the positive electrode active material Li 1+x M 3n Mn 1-y A´ y P 1-z E z By mixing O4, it is possible to further combine a relatively high energy density with relatively good cycle performance, and (3) by controlling the number of moles of A' element, Ni element, and Mn element in the positive electrode plate and the resistance of the positive electrode plate to satisfy the ranges of the above formula, it is possible to simultaneously ensure the rapid charging capability and cycle performance of the positive electrode plate, and it is advantageous to obtain a high energy density.

[0006] In some embodiments of the present application,

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[0007] In some embodiments of the present application, the second active cathode material includes a cathode active material that satisfies at least one of the following conditions: (i) y=1, n=0, and the second active cathode material is Li 1+x A'P 1-z E z O4, A' is an Fe element, or A' is an Fe element and an element including one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge, and (ii) 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, and (iii) 0.001≦y≦0.500, 0.9≦n≦1.1, the second positive electrode active material being Li 1+x M 3n Mn 1-y A´ y P 1-z E z O4, and optionally, the second cathode active material is (i) Li 1+x A'P 1-z E z O4, and / or (ii) Li 1+x Mn 1-y A´ y P 1-z E z Includes O4.

[0008] In some embodiments of the present application, the second positive electrode active material has a discharge plateau, and the discharge voltage of at least one of the discharge plateaus is equal to or greater than the discharge cutoff voltage of the first positive electrode active material and is equal to or less than 3.5 V. By satisfying certain conditions, it is possible to further improve the fast charging capability and simultaneously achieve good cycle performance.

[0009] In some embodiments of the present application, 0.0005≦n (Ni) ≦0.0025, 0.0005≦n (Mn) ≦0.0025, 0.00005≦n (A´) ≦0.0015.

[0010] In some embodiments of the present application, 0.0007 ≦ n (Ni) ≦ 0.0016, and 0.0009 ≦ n (Mn) ≦ 0.0016, and 0.0002 ≦ n (A´) ≦ 0.0006, and at least one of the conditions is satisfied.

[0011] In some embodiments of the present application, 0 < R ≦ 1.3, and optionally, 0 < R ≦ 1. By controlling R within a predetermined range, the internal resistance of the electrode plate can be further reduced, and the rapid charging performance and cycle performance can be improved.

[0012] In some embodiments of the present application, M1 is an Mn element.

[0013] In some embodiments of the present application,

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[0014] In some embodiments of the present application,

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[0015] In some embodiments of the present application, the coating mass of the positive electrode active material layer is 15.50 mg / cm 2 ~20.78mg / cm 2 and selectively 16.80 mg / cm 2 ~18.83mg / cm 2 By controlling the coating mass of the positive electrode active material layer within a predetermined range, it is possible to further improve the rapid charging performance and simultaneously achieve both good energy density and good cycle performance.

[0016] In some embodiments of the present application, the positive electrode active material layer has a compacted density of 2.4 g / cm 3 ~3.40g / cm 3 and selectively 2.6 g / cm 3 ~3.25g / cm 3 is.

[0017] In some embodiments of the present application, the first positive electrode active material has a Dv50 particle size of 2.1 μm to 6.3 μm, and optionally 3.5 μm to 4.9 μm.

[0018] 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, and selectively 0.5m 2 / g~0.9m 2 / g.

[0019] In some embodiments of the present application, the second positive electrode active material has a Dv50 particle size of 0.25 μm to 1.49 μm, and optionally 0.5 μm to 0.9 μm.

[0020] In some embodiments of the present application, the specific surface area of ​​the second positive electrode active material is 9.0 m 2 / g~23.2m 2 / g, and selectively 10.5m 2 / g~17.9m 2 / g.

[0021] In some embodiments of the present application, a first coating layer is provided on the surface of the first positive electrode active material, and optionally, the first coating layer contains one or more elements of Ti, Al, B, Nb, Zr, Si, and W. The provision of the first coating layer can reduce side reactions between the first positive electrode active material and the electrolyte, and improve the stability of the positive electrode active material structure, thereby improving cycle performance and safety.

[0022] In some embodiments of the present application, the thickness of the first coating layer is 20 nm to 150 nm.

[0023] In some embodiments of the present application, a second coating layer is provided on the surface of the second positive electrode active material, and optionally the second coating layer includes at least one of pyrophosphate, phosphate, and carbon. The provision of the second coating layer not only reduces side reactions between the second positive electrode active material and the electrolyte, but also prevents or suppresses the leaching of transition metals or doping elements, while simultaneously improving the structural stability, thereby improving cycle performance and safety.

[0024] In some embodiments of the present application, the second coating layer has a thickness of 10 nm to 50 nm.

[0025] In some embodiments of the present application, E includes at least one of B, Si, N, and S in the second positive electrode active material.

[0026] In some embodiments of the present application, in the second positive electrode active material, A′ includes at least one of Fe, Ti, V, and Mg.

[0027] A second aspect of the present application provides a secondary battery including the positive electrode plate of the first aspect of the present application.

[0028] A third aspect of the present application provides a power consuming device including the positive electrode plate of the first aspect of the present application and / or the secondary battery according to the second aspect of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present application will be further described below in conjunction with the detailed description of the present invention. It should be understood that these specific embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0030] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. Appearances of this phrase in various locations throughout the specification do not necessarily refer to the same embodiment, nor are they mutually exclusive, independent, or alternative embodiments. Those skilled in the art can explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0031] The "ranges" disclosed in this application are defined in the form of a lower limit and / or an upper limit. A given range is defined by selecting a lower limit and / or an upper limit, and the selected lower and / or upper limit define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values, and may be arbitrarily combined; that is, any lower limit and any upper limit may be combined to form an unspecified range, any lower limit and any other lower limit may be combined to form an unspecified range, and similarly, any upper limit and any other upper limit may be combined to form an unspecified range. Furthermore, each point or single numerical value disclosed alone may itself be combined with any other point or single numerical value as a lower or upper limit, or with any other lower or upper limit, to form an unspecified range. For example, if a range of 150 or less is listed for a particular parameter, it is understood that ranges below 150, such as 10 to 140 and 20 to 120, are also contemplated. Note that if 2.1 and 3.5 are listed as minimum range values ​​and 4.9 and 6.3 are listed as maximum range values, then the ranges 2.1 to 6.3, 2.1 to 4.9, 3.5 to 6.3, and 3.5 to 4.9 are all possible ranges. Unless otherwise specified, in this application, a numerical range, e.g., "10 to 50," represents a shorthand expression for any combination of real numbers between 10 and 50, where 10 and 50 are both real numbers. For example, the numerical range "20 to 30" represents that all real numbers between "20 and 30" have already been listed in this specification, and "20 to 30" is merely a shorthand expression for this combination of numbers.

[0032] Unless otherwise stated, 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 content of the present application.

[0033] Unless otherwise stated, all technical features and optional technical features 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 content of the present application.

[0034] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, a description of a method including steps S1 and S2 means that the method may include steps S1 and S2 performed in order, or steps S2 and S1 performed in order. For example, the above-mentioned method may further include step S3, indicating that step S3 can be added to the method in any order, e.g., 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.

[0035] Unless otherwise specified, the terms "comprise" and "include" used in this application may be open ended or closed ended. For example, the terms "comprise" and "include" may further include or include other components not listed, or may include or include only the listed components. Also, in this application, the terms "plurality" and "various" refer to two or more.

[0036] Unless otherwise specified, the term "and / or" in this application merely describes the relationship between related objects and indicates that three relationships may exist, for example, A and / or B may represent three cases: A alone, a combination of A and B, and B alone. In addition, the character " / " in this specification generally indicates that the related objects before and after are in an "or" relationship.

[0037] 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 of this application. The terms used in this application are only for describing specific examples and are not intended to limit this application. The terms "comprises" and "having" and any variations thereof in the specification and claims of this application are intended to cover a non-exclusive "comprise." Unless otherwise specified, terms used in this application have the known meaning commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of each parameter mentioned in this application can be measured using various measurement methods commonly used in the art (for example, can be tested using the methods in the examples of this application).

[0038] Currently, fast charge performance and cycle performance have become important performance indicators for lithium batteries. Currently, positive electrodes are often manufactured using ternary layered positive electrode active materials (e.g., NCM). However, this type of positive electrode material can cause problems such as increased internal resistance and electrode polarization as the number of cycles and discharge time increase. It can also cause the discharge voltage to reach the cutoff voltage prematurely, leading to a tendency for the discharge voltage to drop sharply at the end of discharge, resulting in early termination of discharge and affecting the actual usable capacity of the battery. In other words, this type of positive electrode material has a relatively poor rate tolerance boundary at low SOC, which affects the fast charge and cycle performance of the battery.

[0039] In view of this, a first aspect of the present application provides a positive electrode plate, wherein the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, and the first positive electrode active material is Li a Ni b Co c M 1d M 2e O f R´ gcomprising, 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, and f + g ≦ 3; M1 is an Mn element and / or an Al element; M2 contains one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb; R´ contains one or more elements selected from N, F, S, and Cl; and the second positive electrode active material is Li 1+x M 3n Mn 1-y A´ y P 1-z E z contains LiM 1-y A´ y PO4, where -0.100 ≦ x ≦ 0.100, 0 ≦ n ≦ 1.1, 0.001 ≦ y ≦ 1, and 0 ≦ z ≦ 0.100; M3 contains one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; A´ contains one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge; E contains one or more elements selected from B, Si, N, S, F, Cl, and Br; and the positive electrode plate [Number] satisfies where n (A´) is the molar amount of A´ in the positive electrode plate, with the unit of mol; n (Ni) is the molar amount of Ni in the positive electrode plate, with the unit of mol; n (Mn) is the molar amount of Mn in the positive electrode plate, with the unit of mol; and R is the resistance of the positive electrode plate at 25 °C, with the unit of Ω.

[0040] The inventor of the present application discovered the following: For the layered positive electrode active material system Li a Ni b Co c M 1d M 2e O f R´ g has a relatively poor rate resistance boundary at low SOC regions. The positive electrode active material Li 1+x M 3n Mn 1-y A´<00---0117>P1-z E z O4 has a low-voltage discharge plateau (generally 3.5 V or less) near the end of discharge, and by mixing it with the layered positive electrode active material, Li 1+x M 3n Mn 1-y A´ y P 1-z E z The discharge curve of the composite positive electrode active material after mixing has a discharge plateau at the end of the entire discharge curve, and when the battery is discharged to this plateau, the change in the battery voltage with the capacity is relatively small. This is equivalent to a constant voltage discharge to a certain extent for the layered positive electrode active material, which can mitigate the polarization effect in the discharge process at the previous low voltage point and improve the actual usable capacity. In addition, the positive electrode active material Li 1+x M 3n Mn 1-y A´ y P 1-z E z O4 is further limited by the problem of relatively poor rate tolerance boundary at high SOC, which is due to the layered cathode active material Li a Ni b Co c M 1d M 2e O f R´ g By using it in combination with Li, the defects of the two systems can be compensated for at the same time, and the rate tolerance boundary at high and low SOC points can be expanded, thereby improving the fast charging capability and achieving both cycle performance. a Ni b Co c M 1d M 2e O f R´ g The energy density of 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, and by combining the two, it is possible to achieve both a relatively high energy density and relatively good cycle performance. Furthermore, the positive electrode active material Li1+x M 3n Mn 1-y A´ y P 1-z E z The lattice contraction rate of O4 during the charge and discharge process is relatively large, and mixing the two systems of positive active materials is advantageous for better matching the expansion of the battery negative plate and improving the long-term performance of the battery. Furthermore, the inventors have further discovered during the research process that a high Ni content in the positive plate contributes to improving the battery energy density, but a high Ni content will impair the cycle performance; a high Mn content contributes to the cycle performance, but a high Ni content will impair the battery energy density; a high A' element content contributes to improving the cycle performance, but a high A' element content will impair the battery energy density; and excessively high resistance of the positive plate will also affect the power and cycle performance of the battery. By controlling the mole numbers of A' element, Ni element, and Mn element in the positive plate and the resistance of the positive plate to satisfy the specified ranges of the above formula, it is possible to simultaneously ensure that the positive plate and battery have good fast charging capability and relatively good cycle performance, and is advantageous to obtaining high energy density.

[0041] Furthermore, through extensive research, the inventors have discovered that, in addition to satisfying the above conditions, the performance of the positive electrode plate can be further improved by further controlling the molar amounts and / or relative amounts of elements in the positive electrode plate, the selection of the positive electrode active material, the resistance of the plate, the coating amount of the active material layer on the plate, etc. In other words, in addition to satisfying the above conditions, the positive electrode plate selectively satisfies one or more of the following conditions:

[0042] In some embodiments of the present application, the first positive electrode active material is partially Li a Ni b Co c M 1d M 2e O f R´ g All Li a Ni b Co c M 1d M 2e Of R´ g It may be, 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 an Mn element and / or an Al element, M2 contains one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, Nb, and R´ contains one or more elements of N, F, S, Cl. Optionally, 0.5 ≦ b < 1, 0 < c ≦ 0.5, 0 < d ≦ 0.5, and the cathode active material Li a Ni b Co c M 1d M 2e O f R´ g is made to satisfy the conditions within the above-specified range, which is more advantageous for having a relatively high energy density, good cycle performance, and a long cycle life. The cathode active material Li a Ni b Co c M 1d M 2e O f R´ g In this case, taking the nickel-cobalt-manganese ternary cathode active material (i.e., NCM) system as an example, by increasing the nickel content, the volumetric energy density of the cathode material can be improved, and by increasing the manganese content, the material cost can be reduced, the safety and structural stability of the material can be improved, and the cycle performance can be enhanced. However, if the manganese content is too high, the layered structure of the material will be destroyed, and the specific capacity of the material will decrease. Cobalt can stabilize the layered structure of the material and improve the cycle and rate performance of the material. However, too high cobalt content will cause a decrease in the actual capacity. By making the nickel-cobalt-manganese content satisfy the conditions within the above-specified range, it is advantageous for the cathode plate and the battery to have a relatively high energy density, good rate performance, and cycle performance. Optionally, M1 may be an Mn element, and the first cathode active material may be an NCM-based cathode active material. At this time, its general formula is Li a Ni b Co c Mn d M 2e Of R´ g For example, it may be a nickel-cobalt-manganese ternary layered positive electrode active material.

[0043] In some embodiments of the present application, the second positive electrode active material is partially Li 1+x M 3n Mn 1-y A´ y P 1-z E z O4, 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 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, and is selected from the group consisting of lithium site, manganese site, and phosphorus site. Doping at least one of the elements can help improve the performance of the positive electrode active material, for example, by improving the interfacial performance, reducing the interfacial side reaction with the electrolyte, reducing the antisite defect concentration, and improving the kinetic performance and gram capacity of the material. At the same time, adjusting the manganese site doping element can further improve the particle morphology and the compaction density. Specifically, the lattice volume change rate of the second positive electrode active material during the charge and discharge process is greater than that of the first positive electrode active material. However, a high lattice volume change rate of the positive electrode material is unfavorable for lithium ion transport. Selecting the element A' doped at the manganese site from the above-listed elements contributes to appropriately reducing the lattice change rate during the lithium release process of the material, improving the structural stability of the positive electrode material, reducing the elution of the manganese site element, and reducing the oxygen activity on the particle surface, further improving the gram capacity of the material, and reducing interfacial side reactions with the electrolyte during use, thereby further improving the cycling performance of the material. Selecting the element E doped at the phosphorus site from the above-listed elements also contributes to changing the difficulty of the Mn-O bond length, thereby improving electronic conductivity and lowering the lithium ion migration barrier, facilitating lithium ion migration, and improving rate performance and fast charging performance. Similarly, selecting the element M3 doped at the lithium site from the above-listed elements also contributes to improving the lattice change rate of the material and maintaining the capacity of the material. A too small value of x reduces the lithium content of the entire core system, affecting the gram capacity of the material.The value of y limits the total amount of all doping elements, affecting the manganese content in the system and the voltage plateau of the material. Since the E element is doped at the phosphorus site and the PO tetrahedron is relatively stable, a too large z value will affect the stability of the material. When x, y, and z are selected within the above ranges, the positive electrode active material can have better performance. Furthermore, by selecting the above doping elements and the values ​​of x, n, y, and z, Li can be obtained. 1+x M 3n Mn 1-y A´ y P 1-z E z O4 can maintain electrical neutrality, which can ensure that defects and heterophases in the positive electrode active material are minimized. Taking lithium manganese phosphate-based positive electrode active materials as an example, when excess transition metals (e.g., manganese) are present, the structure of the material system itself is relatively stable, so there is a high possibility that the excess transition metal will precipitate in a simple form or form a heterophase within the crystal lattice. Maintaining electrical neutrality can minimize such heterophases, and by ensuring the electrical neutrality of the system, lithium vacancies can be generated in the positive electrode active material in some cases, thereby improving the dynamic performance of the positive electrode active material. This is advantageous for achieving relatively good cycle performance and high-temperature stability, as well as a relatively large gram capacity and a relatively large compaction density, compared to materials such as lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate that are applicable to conventional high-voltage systems. As can be understood, in the "manganese site" doping described in this application, the manganese site is present in the positive electrode active material Li 1+x M 3n Mn 1-y A´ y P 1-z E z The value of y represents only the position of the manganese element or the A' element in the O4 crystal lattice, and does not necessarily indicate that the manganese element is present at the manganese site. The manganese element at the manganese site may be partially or completely replaced by the A' element. For example, when the value of y 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 element, for example, it may contain iron element at the manganese site, or may contain iron element and other doping elements at the same time.

[0044] 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 of B, Si, N, and S. By selecting the element E doped into phosphorus site from a predetermined range, it further contributes to changing the difficulty of changing the Mn-O bond length, thereby improving the electronic conductivity and lowering the lithium ion migration barrier, facilitating the lithium ion migration, and improving the rate performance and fast charging performance of the material.

[0045] 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, A' may include one or more elements selected from Fe, Ti, V, and Mg. Optionally, A' may be Fe, or more optionally, A' may be at least two elements selected from Fe, Ti, V, and Mg, or even more optionally, A' may be Fe and one or more elements selected from Ti, V, and Mg. By selecting the element A' doped into the manganese site from a predetermined range, the structural stability, gram capacity, cycle performance, rate performance, etc. of the positive electrode material can be further improved, resulting in a positive electrode plate that combines relatively good cycle life and fast charging performance.

[0046] 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 Ez In O4, the manganese site and phosphorus site can be simultaneously doped, which effectively reduces the elution of manganese site elements, further reduces the manganese site ions migrating to the negative electrode, reduces the amount of electrolyte consumed due to the decomposition of the SEI film, and not only improves the cycle performance and safety performance of the battery, but also promotes the adjustment of Mn-O bonds, lowers the lithium ion migration barrier, promotes lithium ion migration, and improves rate performance and fast charge performance. Furthermore, selectively, simultaneous doping of the lithium site, manganese site, and phosphorus site can further achieve significantly improved rate performance, improved cycle performance, and / or high-temperature stability.

[0047] In the present application, the first positive electrode active material has the chemical formula Li a Ni b Co c M 1d M 2e O f R´ g and the second positive electrode active material has the chemical formula Li 1+x M 3n Mn 1-y A´ y P 1-z E z For O4, unless otherwise specified, when a doping site has two or more elements, the limitation on the numerical range of the stoichiometric number of the corresponding doping site element in the chemical formula is not only a limitation on the stoichiometric number of each element in this site, but also a limitation on the sum of the stoichiometric numbers of each element in this site. For example, for the second positive electrode active material Li 1+x M 3n Mn 1-y A´ y P 1-z E z Take the chemical formula of O4 as an example, A1' has two or more elements A1', A2'...A n If ', then A1', A2'...A n ´ each stoichiometric number y1, y2……y n are each within the numerical range defined for y in this application, and y1, y2...y nThe sum of M3 and E must also be within this range. Similarly, when M3 or E is two or more elements, the limitations on the range of the stoichiometric numbers of M3 and E in this application also have the same meanings as above.

[0048] In some embodiments of the present application,

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[0049] In some embodiments of the present application, the positive plate comprises:

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[0050] In this application, the molar amount of each element in the positive electrode plate can be obtained by ICP testing, and can be performed, for example, by the following procedure: about 0.4 g (accuracy to 0.0001 g) of a dry positive electrode plate or 0.1 g (accuracy to 0.0001 g) of a wet positive electrode plate is placed in a 30 ml digestion tank, and one digestion tank without sample is left as a blank sample. The digestion tank containing the positive electrode plate sample is moved into a ventilation cabinet and 12 ml of reverse aqua regia is added. When adding reverse aqua regia, the reverse aqua regia is added along the inner wall of the digestion tank, and the sample remaining on the inner wall is allowed to flow to the bottom of the tank. Then, the top cover, insulating sleeve, gasket, microwave digestion device, and nut are attached in that order, and the nut is tightened with a wrench. Then, the microwave digestion device is started, and the optical fiber sensor in the microwave digestion device is inserted into the bottom of the digestion tank containing the previously assembled sample, and the digestion tank is opened. Place the decomposition tank in a microwave decomposition apparatus to equilibrate, and start the decomposition (the decomposition program is to heat to 120°C in 6 minutes and hold for 8 minutes, then heat to 160°C in 5 minutes and hold for 8 minutes, then heat to 180°C in 5 minutes and hold for 5 minutes). After completion, cool to room temperature and remove it. Place the decomposition tank in a ventilation cabinet, loosen the nuts slowly to ventilate, remove the previously installed parts one by one, transfer the solution in the decomposition tank to a 100ml measuring flask through a funnel (which should be lined with filter paper), then rinse the decomposition tank with ultrapure water, and transfer the rinse solution to a measuring flask, using 10ml of ultrapure water for each rinse. Shake the solution in the 100ml measuring flask evenly, pipette 1ml of the shaken solution into another 100ml measuring flask, then add ultrapure water to make the volume (the solution will reach a total of 100ml). Finally, test the sample solution using ICP-OES. Here, when preparing reverse aqua regia, 1000 ml of ultrapure water can be poured into a 2500 ml glass bottle, followed by 750 ml of concentrated nitric acid and 250 ml of concentrated hydrochloric acid, and then stirred uniformly before use. The concentrated nitric acid can be a commercially available concentrated nitric acid solution with a mass fraction of 68%, and the concentrated hydrochloric acid can be a commercially available concentrated hydrochloric acid with a mass fraction of 68%. Alternatively, hydrogen chloride gas can be added to ultrapure water so that the mass occupancies of hydrogen chloride gas and ultrapure water are 68% and 32%, respectively, and the required concentrated hydrochloric acid can be obtained after complete dissolution.

[0051] In this application, the resistance of the positive electrode plate can be tested at room temperature using a BER1300 film resistance meter. The test steps can be as follows: (1) fabricate the electrode plate into a wafer with a diameter of 22 mm; (2) place the fabricated wafer on the test plate of the BER1300 instrument; (3) adjust the test pressure of the instrument to 0.4 tons, adjust the test time to 10 seconds, and start the test. The obtained resistance value is the film resistance.

[0052] In some embodiments of the present application, the second positive electrode active material is a lithium manganese phosphate-based, lithium iron phosphate-based, lithium manganese iron phosphate-based, or other lithium manganese iron phosphate-based material having the above general formula Li 1+x M 3n Mn 1-y A´ y P 1-z E z O4, for example, the second positive electrode active material may include a positive electrode active material that satisfies at least one of the following three conditions: (i) y = 1, n = 0, and the second positive electrode active material is Li 1+x A'P 1-z E z O4, and A' may be Fe, or A' may be Fe and may include one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge, i.e., the second positive electrode active material may include lithium iron phosphate or lithium iron phosphate doped at at least one of the iron site (the same as the manganese site) and the phosphorus site. (ii) 0.001≦y≦0.500, n=0, and in this case, the second positive electrode active material may include Li 1+x Mn 1-y A´ y P 1-z E zThe compound LiMnPO4 may be lithium manganese phosphate or lithium manganese phosphate doped at least one of the lithium site, manganese site, and phosphorus site. In this application, the lithium manganese phosphate is modified to significantly reduce the dissolution of elements at the manganese site and reduce the lattice change rate, which is advantageous for use in secondary batteries to improve the cycle performance, rate performance, and safety performance of the battery and to increase the capacity of the battery. For example, by doping a specific element in a specific amount at the lithium site, manganese site, and phosphorus site of the compound LiMnPO4, improved rate performance can be obtained, and at the same time, the dissolution of Mn and the doping element at the Mn site can be reduced, improving cycle performance and / or high-temperature stability, and also improving the gram capacity and compaction density of the positive electrode active material. A specific example is Li 1+x Mn 1-y A´ y P 1-z E z O4 is Li 1+x Mn 1-y Fe y P 1-z E z O4, and compared to lithium iron phosphate, lithium manganese iron phosphate has a higher voltage plateau and, when the specific capacity is the same, it has a higher energy density; and (iii) 0.001≦y≦0.500, 0.9≦n≦1.1, at which time 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 lithium manganese phosphate-based second positive electrode active material, the y value limits the total amount of all doping elements. If y is too small, i.e., the doping amount is too small, the doping elements will not work. If y is greater than 0.5, the Mn content in the system will be relatively low, which will affect the voltage plateau of the material. The value of y is preferably in the range of 0.001 to 0.500, more preferably 0.25 to 0.5. It should be noted that the chemical formula Li 1+x A'P 1-z Ez O4, Li 1+x Mn 1-y A´ y P 1-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 located at the same site may be the same or different, but they all have the formula Li 1+x M 3n Mn 1-y A´ y P 1-z E z The stoichiometric number of each element in O4 satisfies a limited numerical range.

[0053] As a specific example, the second positive electrode active material may include a positive electrode active material that satisfies at least one of the following two conditions: (i) y=1, n=0, and the second positive electrode active material is Li 1+x A'P 1-z E z O4, A' is Fe element, or A' contains Fe element and one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge, (ii) 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 Optionally, the second cathode active material has the formula Li 1+x A'P 1-z E z O4 and / or the formula Li 1+x Mn 1-y A´ y P 1-z E z In these two chemical formulas, the values ​​of x and z are independent, but both have the chemical formula Li 1+x M 3n Mn 1-y A´ y P 1-z Ez The stoichiometric numbers of x and z in O4 satisfy a limited numerical range.

[0054] In some embodiments of the present application, the second positive electrode active material has a discharge plateau, and the discharge voltage of at least one discharge plateau is equal to or greater than the discharge cutoff voltage of the first positive electrode active material and is equal to or less than 3.5 V. 1+x M 3n Mn 1-y A´ y P 1-z E z The specific stoichiometry of O4 varies, and its discharge plateau may also vary. For example, if the second positive electrode active material is lithium iron phosphate, there will be only one voltage plateau below 3.5 V. Furthermore, if the second positive electrode active material is lithium manganese phosphate doped at the manganese site, for example, lithium manganese iron phosphate, there will be two discharge plateaus. The present application utilizes the voltage plateau near the end of discharge. By providing the second positive electrode active material with an additional voltage plateau below 3.5 V, this plateau can be used to alleviate polarization during the previous discharge process and further expand the rate tolerance boundary at high and low SOC points after mixing the first and second positive electrode active materials. This improves fast charging capability, balances cycle performance, and improves actual usable capacity.

[0055] In some embodiments of the present application, the molar amount n of Ni element in the positive electrode plate (Ni) (The unit is mol) is 0.0005≦n (Ni) ≦0.0025, for example, n (Ni) may be 0.0008, 0.001, 0.0012, 0.0014, 0.0016, 0.0018, 0.002, 0.0022, 0.0024, etc., or may be a range of any of the above values, optionally 0.0007≦n (Ni)In the positive electrode active material after mixing, the Ni element is provided by the first positive electrode active material, and increasing the content of the Ni element in the first positive electrode active material contributes to improving the battery energy density, but may impair the cycle performance. In the present application, the Ni element content n (Ni) By making the molar amount n of Mn element in the positive electrode plate satisfy the above-mentioned predetermined range, the battery can further have a relatively high energy density and a relatively good cycle performance. (Mn) (The unit is mol) is 0.0005≦n (Mn) ≦0.0025, for example, n (Mn) may be 0.0007, 0.001, 0.0013, 0.0015, 0.0018, 0.002, 0.0021, 0.0023, etc., or may be a range of any of the above values, optionally 0.0009≦n (Mn) ≦0.0016. The molar amount of A' element in the positive electrode plate, n (A´) (The unit is mol) is 0.00005≦n (A´) ≦0.0015, for example, n(A′) may be 0.00008, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.0012, 0.0014, etc., or may be in a range of any of the above values, and optionally, 0.0002≦n (A´) ≦0.0006. In the present application, by further controlling the mole numbers of A′ element and Mn element within a predetermined range, high energy density and relatively good cycle performance of the battery can be further ensured.

[0056] In some embodiments of the present application, the resistance R (unit: Ω) of the positive electrode plate satisfies 0 < R ≤ 1.3. For example, the value of R may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc., or may be within a range consisting of any of the above numerical values. Considering that if the resistance of the positive electrode plate is too high, it will similarly affect the power performance and cycle performance of the battery, it is more advantageous to control the range of the value of R within a predetermined range, so as to endow the positive electrode plate and the battery with relatively good rapid charging performance and cycle performance. Optionally, 0 < R ≤ 1. By further controlling the range of the value of R within a predetermined range, the internal resistance of the battery can be further reduced, and the rapid charging performance and cycle performance can be improved.

[0057] In some embodiments of the present application, the molar amounts of Mn element and A' element in the positive electrode plate are

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[0058] As a specific example, the first positive electrode active material is an NCM-based positive electrode active material Li a Ni b Co c Mn d M 2e O f R´ g It may also be, for example, Li a Ni b Co c Mn d O f R´ g The second positive electrode active material may be a manganese site-doped lithium iron manganese phosphate positive electrode active material Li 1+x Mn 1-y A´ y P 1-z E z O4 (0.001≦y≦0.500), for example, Li 1+x Mn 1-y Fe y P 1-z E zIt may be O4, at this time

number

number

[0059] Here, the occupancy rate of the width of the entire discharge curve of the voltage plateau described in this application can be tested by the single particle microelectrode method, which can be specifically carried out by the following operation steps: particles of the second active material to be dispersed are dispersed on a cover glass washed with a special cleaning solution (H2SO4 (98 wt%): hydrogen peroxide solution (30 wt%) = 3:1 (V / V)) and deionized water; the microelectrode is a Pt microelectrode sealed in a glass capillary; the diameter of the Pt wire is 10 μm, and the end surface is polished to a needle tip shape (the ratio of the glass radius to the Pt wire radius should be less than 5); a copper wire is used as the conductor, and the two are connected by conductive silver paste; and the single particle is Before the test, the microelectrode was placed in a 0.5 mol / L H2SO4 aqueous solution for cyclic voltammetry scanning. The scanning rate was 50 mV / s, and the scanning potential range was -0.22 V to 1.22 V (vs. SCE). The single particle microelectrode testing device mainly included a microelectrode, a microscope, a micromanipulator, and an electrochemical workstation. The microscope and micromanipulator were used to move the microelectrode and bring it into contact with a single particle of the second active material. The particle under test was then used as the working electrode, and the lithium belt was used as the counter and reference electrodes for the electrochemical test. The electrolyte was 1 mol / L LiPF6 / (EC+PC)(V EC :V PC The temperature of the electrochemical test was 25°C, and the battery was charged at a constant current of 0.33C up to 4.4V, followed by constant voltage charging. When the charging current decreased to 0.05C, the constant voltage charging ended, and the battery was subsequently discharged at 0.33C until the full discharge voltage reached 2.5V. The specific capacity-voltage curve of the discharge flow was plotted, with the specific capacity on the X axis and the voltage on the Y axis. The charge capacity at 3.5V was marked Q3, and the total charge capacity was marked Q4. The capacity occupancy rate (i.e., the width of the voltage plateau) when the voltage was less than 3.5V was Q3 / Q4.

[0060] In some embodiments of the present application, the coating mass of the positive electrode active material layer is 15.50 mg / cm 2 ~20.78mg / cm 2 For example, 16.0 mg / cm 2 , 16.50 mg / cm 2, 17.0 mg / cm 2 , 17.50 mg / cm 2 , 18.0 mg / cm 2 , 18.50 mg / cm 2 , 19.0 mg / cm 2 , 19.50 mg / cm 2 , 20.0 mg / cm 2 , 20.5 mg / cm 2 Alternatively, the coating mass of the positive electrode active material layer may be 16.80 mg / cm or less. 2 ~18.83mg / cm 2 Here, if the coating mass of the positive electrode active material layer is too low, on the one hand, it is disadvantageous to improving the battery energy density, and on the other hand, the electrode plate polarization is significantly improved. a Ni b Co c M 1d M 2e O f R´ g The second positive electrode active material Li 1+x M 3n Mn 1-y A´ y P 1-z E z The improvement effect of adding O4 is not significant, and if the coating mass of the positive electrode active material layer is too high, or if the degree of increase in plate polarization is Li 1+x M 3n Mn 1-y A´ y P 1-z E z Beyond the improvement effect of adding O4, it also affects rate performance and fast charge performance. In this application, by controlling the coating mass of the positive electrode active material layer within a predetermined range, the fast charge performance of the battery can be further improved, while simultaneously achieving both energy density and cycle performance.

[0061] In some embodiments of the present application, the positive electrode active material layer has a compacted density of 2.4 g / cm 3 ~3.40g / cm 3 For example, 2.5 g / cm 3 , 2.6g / cm 3 , 2.7g / cm3 , 2.8g / cm 3 , 2.9g / cm 3 , 3.0g / cm 3 , 3.1g / cm 3 , 3.2g / cm 3 , 3.3g / cm 3 or may be any range of values ​​above. Here, the compaction density of the active material lamination of the positive electrode plate can be measured in accordance with GB / T 24533-2009. If the compaction density of the positive electrode active material layer in the positive electrode plate is too low, the contact between particles inside the plate is likely to loosen, increasing contact resistance. However, if the compaction density of the positive electrode active material layer in the positive electrode plate is too high, two problems will occur. First, some particles inside the plate will be easily crushed / cracked after cold pressing, and the crushed particles / cracks will likely react with the electrolyte, causing a decrease in battery performance. During battery cycling, the internal pressure of the plate will be high, causing particles to be pressed against each other and easily crushed. Second, the porosity of the plate will decrease, making it more difficult for the electrolyte to infiltrate, further causing a decrease in battery performance. In the present application, by controlling the packing density of the active material layer of the positive electrode plate within a predetermined range, it is possible to improve the polarization problem of the electrode plate and to advantageously improve the cycle performance and long-term use performance of the battery. Optionally, the packing density of the active material layer of the positive electrode plate is 2.6 g / cm 3 ~3.25g / cm 3 This can further improve the cycle performance and long-term use performance of the battery.

[0062] 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 may be, for example, 2.4 μm, 2.7 μm, 3.0 μm, 3.3 μm, 3.6 μm, 3.9 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.1 μm, 5.4 μm, 5.7 μm, 6.0 μm, or any range of the above values. The Dv50 of the first positive electrode active material refers to the particle size corresponding to 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 using laser diffraction particle size analysis, for example, by using a laser particle size analyzer (e.g., a Malvern Master Size 3000) according to standard GB / T 19077-2016. In the present application, controlling the Dv50 particle size of the first positive electrode active material within a predetermined range is beneficial for preventing crushing or powdering during charging and discharging, thereby reducing battery capacity loss and shortening the diffusion path of active ions, thereby increasing the electron conduction rate and improving the battery's cycle performance. At the same time, it also provides the active material with adequate active sites. A particle size that is too small results in a relatively large number of active sites, which increases side reactions during the material's cycle process and significantly adversely affects cycle performance. A particle size that is too large results in a relatively small number of active sites, which significantly adversely affects power performance. Furthermore, controlling the Dv50 particle size of the first positive electrode active material within a predetermined range based on the thickness of the first coating layer can further ensure that the battery has a relatively high energy density. Optionally, the Dv50 particle size of the first positive electrode active material may be 3.5 μm to 4.9 μm, which further achieves high energy density, relatively good power performance, and cycle performance, and improves fast charging capability and service life.

[0063] In some embodiments of the present application, the Dv50 particle size of the second positive electrode active material may be 0.25 μm to 1.49 μm, such as 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, or 1.4 μm, or may be any range of values ​​above. 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 using laser diffraction particle size analysis, for example, by using a laser particle size analyzer (e.g., a Malvern Master Size 3000) according to standard GB / T 19077-2016. In the present application, controlling the Dv50 particle size of the second positive electrode active material within a predetermined range is advantageous in preventing crushing or powdering during charge and discharge, thereby reducing capacity loss and shortening the diffusion path of active ions, improving electron conduction rate, and improving cycle performance. At the same time, the active material has adequate active sites, enabling both cycle performance and power performance to be achieved. Furthermore, controlling the Dv50 particle size of the second positive electrode active material within a predetermined range is advantageous in achieving a desired compaction density in accordance with the Dv50 particle size range of the first positive electrode active material, thereby avoiding relatively large interparticle voids in the positive electrode active material. Optionally, the Dv50 particle size of the second positive electrode active material may be 0.5 μm to 0.9 μm, which further achieves a high energy density, relatively good power performance, and cycle performance, and improves fast charging capability and service life.

[0064] 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, 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, 1.1m2 / g, or may be in a range of any value above 0.5 m 2 / g~0.9m 2 Further, the specific surface area of ​​the second positive electrode active material may be 9.0 m / g. 2 / g~23.2m 2 / g, for example 10m 2 / g, 11m 2 / 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, or may be in a range of any value therein or greater, and optionally the specific surface area of ​​the second positive electrode active material may be 10.5 m 2 / g~17.9m 2 / g. In the present application, the specific surface areas of the first and second positive electrode active materials can be measured using conventional methods in the art, such as nitrogen physical adsorption. Increasing the specific surface area contributes to an increase in the active sites of the positive electrode active material, which is advantageous for providing the material with relatively good power performance. However, these increased active sites also increase side reactions during the cycling process of the positive electrode active material, thereby causing a decline in the cycling performance of the material. In the present application, by controlling the specific surface areas of the first and second positive electrode active materials within a predetermined range, relatively good power performance and cycle life can be obtained, and the fast charging capability and service life can be improved.

[0065] 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 contain 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 not only prevents contact between the positive electrode active material and the electrolyte, but also reduces side reactions between the positive electrode active material and the electrolyte, improving the structural stability of the positive electrode active material and the cycle stability and safety of the material. The elements in the first coating layer may be provided in the form of oxides (e.g., Al2O3, ZrO2, TiO2, Nb2O3, etc.) or lithium compounds. The inclusion of the elements in the first coating layer in the above-described ranges improves the ionic conductivity of the material surface, improves the rate performance and gram capacity of the material, stabilizes the material structure, prevents direct contact between the material and the electrolyte, and improves cycle performance.

[0066] In some embodiments of the present application, the thickness of the first coating layer may be 20 nm to 150 nm, such as 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, etc., or any range of the foregoing values. If the thickness of the first coating layer is too thin, the possibility of rupture / deep damage to the positive electrode active material during use increases, significantly reducing the performance-enhancing and protective effect of the first positive electrode active material; if the thickness of the first coating layer is too thick, lithium ions will need a longer transport path from the electrolyte to the active material system, significantly affecting the performance of the active material; and when the coating layer sinters, the coating material will react with lithium in the internal material, reducing the available active lithium in the material and the corresponding gram capacity of the material. In the present application, by controlling the thickness of the first coating layer within the above-mentioned predetermined 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.

[0067] 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 not only prevents contact between the second positive electrode active material and the electrolyte, thereby reducing side reactions between the second positive electrode active material and the electrolyte, but also prevents or suppresses the leaching of transition metals or doping elements from the second positive electrode active material, improving its structural stability and further 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. Metal ions are less likely to migrate in pyrophosphate. Selecting pyrophosphate as the coating layer material can effectively isolate the metal ions doped in the positive electrode material from the electrolyte. Furthermore, the pyrophosphate is preferably crystalline, which stabilizes the structure of the crystalline pyrophosphate and effectively suppresses the leaching of transition metals from the active material, improving cycle performance. The phosphate coating can improve the ion transport performance of the positive electrode material and is advantageous for promoting lithium ion transport. Furthermore, the phosphate can be a crystalline phosphate, which has a relatively high lattice match with crystalline pyrophosphate, and has high stability and excellent lithium ion conductivity. Coating the second positive electrode active material with this improves the stability of the positive electrode active material and effectively reduces interfacial side reactions with the electrolyte, thereby improving the high-temperature cycle and storage performance of the battery. The carbon coating can effectively improve the conductive performance and desolvation ability of the positive electrode active material. Carbon materials have good electronic conductivity, and when applied to batteries, electrochemical reactions occur, requiring the participation of electrons. To increase electron transmission between particles and between different locations on the particles, carbon with excellent conductive properties can be used to coat the positive electrode active material.As can be understood, when the second coating layer simultaneously contains pyrophosphate, phosphate, and carbon, the pyrophosphate, phosphate, and carbon may 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 may be formed in this order on the surface of the second positive electrode active material; a phosphate coating layer, a pyrophosphate coating layer, and a carbon coating layer may be formed in this order on the surface of the second positive electrode active material; or a composite coating layer of pyrophosphate and phosphate may be formed on the surface of the second positive electrode active material, and then a carbon coating layer may be formed on the surface of the composite coating layer.

[0068] 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, etc., or may be any range of the above values. Controlling the thickness of the second coating layer within a predetermined range not only effectively inhibits the elution of transition metals or doping elements in the second positive electrode active material and reduces the lattice change rate of the second positive electrode active material, but also prevents an excessive coating thickness from affecting lithium ion migration and battery energy density, and further improves the dynamic performance, cycling performance, and safety of the battery without sacrificing the gram capacity of the second positive electrode active material.

[0069] 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 a crystalline pyrophosphate, the second sub-coating layer may include a crystalline phosphate and coat the first sub-coating layer, and the third sub-coating layer may be carbon and coat the second sub-coating layer. The pyrophosphate, as the first sub-coating layer, can effectively isolate the metal ions doped into the second positive electrode active material from the electrolyte; the crystalline pyrophosphate coating can effectively inhibit the elution of transition metals in the second positive electrode active material and improve cycle performance; the crystalline phosphate, as the second sub-coating layer, has a relatively 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 advantageous for improving the stability of the positive electrode active material and reducing interfacial side reactions between the positive electrode active material and the electrolyte; and the third sub-coating layer strengthens interparticle electron transport, improves the electronic conductivity of the positive electrode active material, and effectively improves the conductive performance and desolvation ability of the positive electrode active material.Furthermore, the thickness of the first sub-coating layer may be 1 nm to 10 nm, for example, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, etc., or may be within any range of the above numerical values. When the thickness of the first sub-coating layer is within the predetermined range, it is possible to avoid the adverse effect on the dynamic performance of the positive electrode active material that may occur when the thickness of the first sub-coating layer is too thick, and it is possible to avoid the problem of not being able to effectively inhibit the migration of transition metal ions when the thickness is too thin. The thickness of the second sub-coating layer may be 2 nm to 15 nm, for example, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, etc., or may be within any range of the above numerical values. When the thickness of the second sub-coating layer is too large, it may affect the plateau voltage of the entire positive electrode active material. When the thickness of the second sub-coating layer is within a predetermined range, its surface structure is stable, side reactions with the electrolyte are small, and interfacial side reactions 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 2 nm to 25 nm, for example, 4 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, etc., or can be any value within the above range. When the thickness of the third sub-coating layer is within the predetermined range, the conductivity of the positive electrode active material and the compaction density of the positive electrode plate can be improved, and at the same time, the problem of an excessive coating thickness affecting the compaction density of the electrode plate when this sub-coating layer contains amorphous carbon can be avoided.

[0070] Here, in the present application, the thickness dimension test of the coating layer may be performed by FIB, and a specific method may include the following steps: a single particle is randomly selected from the positive electrode active material powder to be measured, a thin slice about 100 nm thick is cut from the middle position or near the middle position of the selected particle, and a TEM test is performed on the thin slice to measure the thickness of the coating layer, measuring 3 to 5 points and calculating the average value.

[0071] A second aspect of the present application provides a secondary battery including the positive electrode plate of the first aspect of the present application.

[0072] A secondary battery generally includes a case assembly, a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, with the positive electrode plate, negative electrode plate, separator, and electrolyte positioned within a cavity formed by the case assembly. Depending on the type of battery, the case assembly may be an aluminum plastic film or metal case assembly, and the metal case assembly may further include a prismatic case assembly or a cylindrical case assembly. When the case assembly is a metal case assembly, it generally includes a case with an opening on at least one side and a lid for sealing the opening. Any type of battery may be considered within the technical scope of the battery of the second aspect of the present application as long as its positive electrode plate includes the positive electrode plate of the first aspect of the present application. In addition to the aforementioned characteristics of the active material and the compaction density of the active material layer of the positive electrode plate, other structural characteristics or material selection of the positive electrode plate, and the selection of the negative electrode plate, separator, and electrolyte can all be selected according to common selection methods in the art, and those skilled in the art can flexibly select the appropriate materials according to their actual needs.

[0073] In some embodiments of the present application, the secondary battery may be a laminated battery or a wound battery, and the wound battery may be a prismatic battery or a cylindrical battery, or optionally, the battery may be a cylindrical battery. Depending on the type of battery, the positive electrode plate, the negative electrode plate, and the separator may be stacked to form a stacked unit, or may be stacked and then wound to form a wound body.

[0074] In some embodiments of the present application, the battery may be a single battery core or a battery module assembled with battery cores, and the number of battery cores included in the battery module may be multiple, and the specific number may be adjusted based on the application and capacity of the battery module. Furthermore, the battery module may further include a packaging assembly having an accommodating space, and the packaging assembly may include a bottom plate, a side plate, a cover plate, etc.

[0075] In some embodiments of the present application, the above battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0076] The present application also provides a power consuming device including the positive electrode plate of the first aspect of the present application and / or the secondary battery of the second aspect of the present application.

[0077] The secondary battery, such as a battery core, a battery module, or a battery pack, may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. In one specific example, the power consuming device may be a vehicle.

[0078] The power consuming device can select a specific type of battery according to its usage needs, such as a battery core, a battery module, or a battery pack.

[0079] As an example, the power consuming device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, and a battery pack or battery module may be employed to meet the demand for high power output and high energy density of the battery of the power consuming device.

[0080] As another example, the power consuming device may be a mobile phone, a tablet computer, a laptop computer, etc. The power consuming device generally requires a thin design and may employ a battery core as a power source.

[0081] The following examples of the present application are described. The examples described below are illustrative and are used only to interpret the present application and should not be understood as limitations on the present application. Unless specific techniques or conditions are specified in the examples, they are carried out according to the techniques or conditions described in literature in the field or according to the product instructions. Unless the manufacturer is specified, the reagents or equipment used are all commercially available products.

[0082] Secondary battery manufacturing and testing methods: 1. Pouch laminated battery: (1) Manufacturing of positive electrode plate: The positive electrode active material, polyvinylidene fluoride (PVDF), and conductive carbon were added to a certain amount of N-methylpyrrolidone (NMP) so that the mass ratio of positive electrode active material:polyvinylidene fluoride:conductive carbon was 90:5:5. The mixture was stirred in a drying chamber to produce a uniform slurry, and the viscosity was controlled to 3000-10000 mPa·S. The slurry was then applied to aluminum foil and dried to produce a positive electrode plate.

[0083] (2) Manufacturing of negative electrode plates: Graphite, sodium carboxymethylcellulose (CMC), styrene butadiene rubber (SBR), and conductive carbon were added to a certain amount of deionized water in a mass ratio of 90:2:3:5 (graphite:sodium carboxymethylcellulose:styrene butadiene rubber:conductive carbon). The mixture was stirred to produce a uniform slurry, the viscosity of which was controlled to 3000-10000 mPa·S. The slurry was then applied to copper foil and dried to produce a negative electrode plate.

[0084] (3) Pouch laminate battery manufacturing: The resulting positive and negative electrodes and separator (a polyethylene (PE) porous polymer film) are then stacked in a Z-shaped configuration to form a corresponding battery core. The battery core is then vacuum dried at 90°C for 12 hours. The positive and negative tabs are then ultrasonically welded together, with an aluminum tab for the positive electrode and a nickel tab for the negative electrode. The positive and negative tabs are located on the same side of the battery core. After the tabs are welded, the battery core is then placed in an appropriate-sized aluminum plastic film and top-packaged. The typical packaging temperature is 145°C. The electrolyte is then injected (1 mol / L LiPF6 / (ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1) + 5 wt.% fluoroethylene carbonate (FEC)). The battery is then allowed to stand, undergoes formation, aging, venting, secondary packaging, and capacity testing to produce a pouch-laminated battery.

[0085] 2. Conduct a cycle test at 25°C on the manufactured pouch laminate battery: The pouch laminate battery manufactured as above was charged at 0.5C0 from 2.5 to 4.4V in a constant temperature environment of 25°C up to 4.4V, then constant voltage charged at 4.4V until the current was ≦0.05C0, left to stand for 5 minutes, and then discharged at 1C0 down to 2.5V. The capacity was measured. n (n=1, 2, 3……) and repeat the above operation. The capacity retention rate is C n / C3 ratio, C n When / C3×100%=80%, the corresponding number of cycles is extracted and used as an index for assessing cycle capability.

[0086] 3. Positive electrode plate membrane resistance test: The film resistance was tested using a BER1300 film resistance meter. The test steps were as follows: (a) the electrode plate was fabricated into a wafer with a diameter of 22 mm, (b) the fabricated wafer was placed on the test plate of the BER1300 instrument, (c) the test pressure of the instrument was adjusted to 0.4 T, the test temperature to 25°C, and the test time to 10 seconds, and then the test was started. The obtained resistance value was the film resistance.

[0087] 4. 10%~80% SOC charging time experiment: First, a capacity test was conducted on the pouch laminate battery. The procedure was as follows: constant current charging at 0.33C up to a full charge voltage V1, then switching to constant voltage charging. When the charging current decreased to 0.05C, the constant voltage charging ended, followed by discharging at 0.33C down to a full discharge voltage V2. This procedure was repeated three times, and the capacity result of the third test was used as the basis. At the same time, the gram capacity of the positive electrode was calculated using the third test result.

[0088] Different rates for pouch laminate batteries (C1 <C2<C3<C4<……<C n ) charging test, during which the charge rate must be increased from low to high, and the total electrical voltage of the pouch laminated battery and the negative electrode voltage of the pouch laminated battery must be monitored simultaneously during the charging process. The detailed process is as follows: the pouch laminated battery is charged at C1 until the full charge voltage V1 or the negative electrode voltage reaches 0V, and the battery SOC value at the end of charge is extracted. It is then discharged at 0.33C until the full discharge voltage V2 is reached. By repeating the above process, the SOC value at the end of charge can be obtained at different rates. A scatter plot of the SOC at the end of charge versus the rate is created and fitted to obtain the relationship between the SOC at the end of charge and the rate. 20%, 30%, 40%, 50%, 60%, 70%, and 80% are substituted into the relationship equation to obtain the corresponding rate (C 20% , C 30% , C 40% , C 50% , C 60% , C70% , C 80% After obtaining the value, the 10%~80% SOC charging time can be calculated, where 10%~80% SOC charging time = (60 / C 20% +60 / C 30% +……+60 / C 80% )×10%.

[0089] Example 1 For pouch laminate batteries: (i) Positive electrode plate: The number of layers of the positive electrode plate is 15, the thickness of the single-layer positive electrode plate is 0.13 mm, and the compaction density of the active material layer of the positive electrode plate is 3.1 g / cm 3 The first positive electrode active material is NCM523, the Dv50 particle size of the first positive electrode active material is 4.1 μm, and the specific surface area of ​​the first positive electrode active material is 0.6 m 2 / g, and 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 0.83 μm, and the specific surface area of ​​the second positive electrode active material is 12.5 m 2 / g, and the positive electrode plate has A' as Fe,

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[0090] (ii) Negative electrode plate: The number of layers of the negative electrode plate is 16, the thickness of the single-layer negative electrode plate is 0.13 mm, and the compaction density of the active material layer of the negative electrode plate is 1.68 g / cm 3 is.

[0091] (iii) Separator: The number of layers of the separator is 16, and the thickness of the single-layer separator is 0.011 mm.

[0092] (iv) The thickness of the internal cavity of the battery case is 5.9 mm; (vi) The electrolyte filling coefficient of the secondary battery is 2.73 g / Ah.

[0093] Examples 2 to 16 and Comparative Examples 1 to 4 The differences between Examples 2 to 16 and Comparative Examples 1 to 4 and Example 1 are:

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[0094] The batteries assembled in Examples 1 to 16 and Comparative Examples 1 to 4 were tested, and the test results are shown in Table 1.

[0095] [Table 1-1] [Table 1-2]

[0096] Results and conclusions: As can be seen from the above examples and comparative examples, by adopting the battery design proposal of the present application, the cycle performance and fast charging performance of the battery can be improved.

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[0097] Finally, it should be noted that the above embodiments are merely for illustrating the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications may still be made to the technical solutions described in the above embodiments, or equivalent substitutions may be made for some or all of the technical features therein. Such modifications or substitutions do not deviate from the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and should all be included in the scope of the claims and description of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in the embodiments may be combined in any manner. The present application is not limited to the specific embodiments disclosed in the description, but includes all technical solutions included within the scope of the claims.

Claims

1. A positive electrode plate, wherein the positive electrode plate includes a positive electrode active material layer, the positive electrode active material layer including a first positive electrode active material and a second positive electrode active material; The first positive electrode active material is Li ａ Ni ｂ Co ｃ M １ｄ M ２ｅ O ｆ R' ｇ wherein 0.75≦a≦1.2, 0<b<1, 0<c<1, 0<d<1, 0≦e≦0.2, 1≦f≦2.5, 0≦g≦1, f+g≦3; and M １ is Mn element and / or Al element, M ２ R' includes one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb; and R' includes one or more elements of N, F, S, and Cl; The second positive electrode active material is 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≦1, 0≦z≦0.100, and M ３ comprises one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W; A' comprises one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb and Ge; E comprises one or more elements of B, Si, N, S, F, Cl and Br; The positive electrode plate is [Equation 1] Fulfilling Here, n （Ａ´） is the molar amount of A' in the positive electrode plate, and the unit is mol, and n （Ｎｉ） is the molar amount of Ni in the positive electrode plate, and the unit is mol, and n （Ｍｎ） is the molar amount of Mn in the positive electrode plate, and its unit is mol; R is the resistance of the positive electrode plate at 25° C., and its unit is Ω; 【Request 2】 【Number 2】 and selectively, [Equation 3] where n （Ｐ） is the molar amount of P in the positive electrode plate, and the unit is mol.

3. The second positive electrode active material includes a positive electrode active material that satisfies at least one of the following conditions: (i) y = 1, n = 0, the second positive electrode active material is Li １＋ｘ A'P １－ｚ E ｚ O ４ and A' is an Fe element, or A' is an Fe element and an element comprising one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb, and Ge; (ii) 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 and (iii) 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 O ４ and Optionally, the second cathode active material is: (i) Li １＋ｘ A'P １－ｚ E ｚ O ４ and / or (ii) Li １＋ｘ Mn １－ｙ A' ｙ P １－ｚ E ｚ O ４ The positive electrode plate according to claim 1 or 2, comprising:

4. 4. The positive electrode plate according to claim 1, wherein the second positive electrode active material has a discharge plateau, and a discharge voltage of at least one of the discharge plateaus is equal to or greater than a discharge cutoff voltage of the first positive electrode active material and is equal to or less than 3.5 V.

5. 0.0005≦n （Ｎｉ） ≦0.0025, 0.0005≦n （Ｍｎ） ≦0.0025, 0.00005≦n （Ａ´） 5. The positive electrode plate according to claim 1, wherein the ρ is ≦0.0015.

6. 0.0007≦n （Ｎｉ） ≦0.0016 and 0.0009≦n （Ｍｎ） ≦0.0016 and 0.0002≦n （Ａ´） The positive electrode plate according to claim 1 , wherein at least one of the conditions of ≦0.0006 is satisfied.

7. 7. The positive electrode plate according to claim 1, wherein 0<R≦1.3, and optionally 0<R≦1.

8. M １ The positive electrode plate according to claim 1 , wherein is a Mn element. 【Request 9】 【Number 4】 and selectively, [Equation 5] and, more selectively, [Equation 6] The positive electrode plate according to any one of claims 1 to 8, 【Request 10】 【Number 7】 and selectively, [Equation 8] The positive electrode plate according to any one of claims 1 to 9,

11. The coating mass of the positive electrode active material layer was 15.50 mg / cm ２ ~20.78mg / cm ２ and optionally 16.80 mg / cm ２ ~18.83mg / cm ２ The positive electrode plate according to any one of claims 1 to 10,

12. The compaction density of the positive electrode active material layer is 2.4 g / cm ３ ~3.40 g / cm ３ and optionally 2.6 g / cm ３ ~3.25g / cm ３ The positive electrode plate according to any one of claims 1 to 11,

13. The positive electrode plate according to any one of claims 1 to 12, wherein the Dv50 particle size of the first positive electrode active material is 2.1 μm to 6.3 μm, optionally 3.5 μm to 4.9 μm.

14. The specific surface area of ​​the first positive electrode active material is 0.3 m ２ / g to 1.2m ２ / g, and optionally 0.5m ２ / g to 0.9m ２ The positive electrode plate according to any one of claims 1 to 13, wherein the SiO2 content is 1 / g.

15. The positive electrode plate according to any one of claims 1 to 14, wherein the Dv50 particle size of the second positive electrode active material is 0.25 μm to 1.49 μm, optionally 0.5 μm to 0.9 μm.

16. The specific surface area of ​​the second positive electrode active material is 9.0 m ２ / g to 23.2m ２ / g, and optionally 10.5m ２ / g to 17.9m ２ The positive electrode plate according to any one of claims 1 to 15, wherein the SiO2 content is 1 / g.

17. 17. The positive electrode plate according to claim 1, wherein a first coating layer is provided on a surface of the first positive electrode active material, and optionally the first coating layer contains one or more elements of Ti, Al, B, Nb, Zr, Si, and W.

18. The positive electrode plate according to claim 17, wherein the thickness of the first coating layer is 20 nm to 150 nm.

19. 19. The positive electrode plate according to claim 1, wherein a second coating layer is provided on a surface of the second positive electrode active material, and optionally, the second coating layer includes at least one of pyrophosphate, phosphate, and carbon.

20. The positive electrode plate according to claim 19, wherein the second coating layer has a thickness of 10 nm to 50 nm.

21. 21. The positive electrode plate according to claim 1, wherein, in the second positive electrode active material, E includes at least one of B, Si, N, and S.

22. The positive electrode plate according to claim 1 , wherein in the second positive electrode active material, A′ includes at least one of Fe, Ti, V, and Mg.

23. A secondary battery comprising the positive electrode plate according to any one of claims 1 to 22.

24. 24. A power consuming device comprising the positive electrode plate according to any one of claims 1 to 22 and / or the secondary battery according to claim 23.

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