Secondary battery and electric device

Abstract

The present application provides a secondary battery and an electric device. In particular, the present application provides a lithium-ion secondary battery. The lithium-ion secondary battery comprises a positive electrode sheet. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on the positive electrode current collector and comprising a positive electrode active material, wherein the positive electrode active material comprises a lithium-containing transition metal oxide and a lithium-containing transition metal phosphate. The lithium-containing transition metal oxide comprises a nickel element, a cobalt element, a manganese element and / or an aluminum element, and a silicon element, and an average mass concentration proportion of the silicon element in an outer region corresponding to a primary particle of the lithium-containing transition metal oxide extending from the surface to one quarter of the radius toward the center is greater than an average mass concentration proportion of the silicon element in a core region corresponding to the primary particle extending from the center to one quarter of the radius toward the surface; and the lithium-containing transition metal phosphate comprises an iron element, and the lithium-containing transition metal phosphate comprises secondary particles formed by agglomeration of primary particles.

Description

Secondary batteries and electrical appliances

[0001] Cross-references

[0002] This application incorporates Chinese Patent Application No. 202411524367.3, filed on October 29, 2024, entitled "Secondary Battery and Electrical Device", which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a lithium-ion secondary battery and an electrical device. Background Technology

[0004] Lithium-ion batteries have gradually become the mainstream choice for portable electronic devices, electric vehicles, and hybrid vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. Among various cathode active materials, lithium-containing transition metal oxides (such as ternary cathode materials, lithium nickel cobalt manganese oxide) are widely used due to their high discharge specific capacity. However, in existing technologies, when lithium-containing transition metal oxides are used as cathode active materials for secondary batteries, it is difficult for the secondary batteries to simultaneously achieve high power density and good cycle performance.

[0005] Therefore, there is a need for a lithium-ion secondary battery that includes a lithium-containing transition metal oxide as the positive electrode active material and has both high power density and good cycle performance. Summary of the Invention

[0006] This application is made in view of the above-mentioned issues, and its purpose is to provide a lithium-ion secondary battery and power device that have both high power density and good cycle performance.

[0007] The inventors have discovered that by adopting the technical solution of this application, the above-mentioned objectives can be achieved.

[0008] The first aspect of this application provides a lithium-ion secondary battery, which includes a positive electrode.

[0009] The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector and including a positive active material, wherein,

[0010] The positive electrode active materials include lithium-containing transition metal oxides and lithium-containing transition metal phosphates.

[0011] Lithium-containing transition metal oxides include nickel, cobalt, manganese, and / or aluminum, as well as silicon. The average mass concentration of silicon in the outer region corresponding to 1 / 4 radius from the surface of the primary particle to the center of the lithium-containing transition metal oxide is greater than the average mass concentration of silicon in the core region corresponding to 1 / 4 radius from the center of the primary particle to the surface.

[0012] Lithium-containing transition metal phosphates include iron, and lithium-containing transition metal phosphates also include secondary particles formed by the agglomeration of primary particles.

[0013] The lithium-ion secondary battery of this application has both high power density and good cycle performance.

[0014] In any embodiment, the porosity of the positive electrode, as measured by ion-polished cross-sectional morphology analysis (CP), is 6%-10%. In any embodiment, the porosity of the positive electrode, as measured by ion-polished cross-sectional morphology analysis (CP), is 7%-9%.

[0015] When the porosity of the positive electrode sheet, as measured by ion polishing cross-sectional morphology analysis (CP), is 7%-9%, the lithium-ion secondary battery of this application has a high power density.

[0016] In any embodiment, the average mass concentration of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface of the lithium transition metal oxide is 0.1%-0.7%.

[0017] In any embodiment, the average mass concentration of silicon in the core region corresponding to 1 / 4 radius of the primary particle center of the lithium transition metal oxide is 0%-0.06%.

[0018] In any embodiment, the average particle size of the primary particles containing lithium transition metal oxide is 1 μm to 5 μm.

[0019] In any embodiment, the volume average particle size Dv50 of the lithium transition metal oxide is from 2 μm to 10 μm.

[0020] In any embodiment, the volume average particle size Dv50 of the lithium transition metal phosphate is from 2 μm to 15 μm.

[0021] In any embodiment, the specific surface area of ​​the lithium-containing transition metal phosphate is 2 m². 2 / g to 10m 2 / g.

[0022] In any embodiment, the lithium-containing transition metal phosphate has the molecular formula Li m1 Fe x Mn r P y O j1 Q1 q1Q1 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.6 ≤ m1 ≤ 1.15, x > 0, r ≥ 0, 0.9 ≤ x + r ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j1 ≤ 4, and 0 ≤ q1 ≤ 0.1.

[0023] In any embodiment, the lithium-containing transition metal oxide has the molecular formula Li m2 (Ni a Co b Mn c ) 1-d Si d O j2 Q2 q2 Q2 includes one or more of Zr, Ti, Nb, Al, P, Sr, W, B, Ba, Mg, Sn, Y, Na, S, N, F, Cl, Br and I, 0.6≤m2≤1.5, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1, 0<d≤0.1, 1.8≤j2≤2, 0≤q2≤0.2, j2+q2=2.

[0024] In any embodiment, the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is from 2:1 to 50:1.

[0025] A second aspect of this application provides an electrical device that includes the lithium-ion secondary battery of the first aspect of this application. Attached Figure Description

[0026] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0027] Figure 2 is an exploded view of a secondary battery according to an embodiment of this application shown in Figure 1;

[0028] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0029] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0030] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0031] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0032] Figure 7 is an ion-polished cross-sectional morphology diagram of a lithium-containing transition metal oxide in one embodiment of this application.

[0033] Figure 8 is an ion-polished cross-sectional morphology diagram of a mixture of lithium-containing transition metal oxide and lithium-containing transition metal phosphate in one embodiment of this application.

[0034] Explanation of reference numerals in the attached drawings: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0035] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the lithium-ion secondary battery and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0039] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0041] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0042] Lithium-ion batteries have gradually become the mainstream choice in portable electronic devices, electric vehicles, and hybrid vehicles due to their advantages such as high energy density, long cycle life, and no memory effect. Among various cathode active materials, lithium-containing transition metal oxides (such as ternary cathode materials, such as lithium nickel cobalt manganese oxide) are widely used due to their high discharge specific capacity. However, in existing technologies, when lithium-containing transition metal oxides are used as cathode active materials in secondary batteries, it is difficult for the secondary batteries to simultaneously achieve high power density and good cycle performance. Therefore, there is a need to provide a lithium-ion secondary battery that incorporates lithium-containing transition metal oxides as cathode active materials and possesses both high power density and good cycle performance.

[0043] Based on this, this application proposes a technical solution to solve the above-mentioned technical problems.

[0044] The first aspect of this application provides a lithium-ion secondary battery, the lithium-ion secondary battery comprising a positive electrode.

[0045] The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on the positive current collector and including a positive active material, wherein...

[0046] The positive electrode active material includes lithium-containing transition metal oxides and lithium-containing transition metal phosphates.

[0047] The lithium-containing transition metal oxide includes nickel, cobalt, manganese, and / or aluminum, as well as silicon. The average mass concentration of silicon in the outer region corresponding to 1 / 4 radius from the surface of the primary particle of the lithium-containing transition metal oxide is greater than the average mass concentration of silicon in the core region corresponding to 1 / 4 radius from the center of the primary particle.

[0048] The lithium-containing transition metal phosphate includes iron, and the lithium-containing transition metal phosphate includes secondary particles formed by the agglomeration of primary particles.

[0049] The surface of primary particles containing lithium transition metal oxides is the part that directly contacts the positive electrode active material and the electrolyte. Side reactions occur and byproducts are deposited on this surface. Interfacial stability is crucial for improving the cycle performance and storage life of secondary batteries, especially in high-voltage (~4.5V) systems. The outer region extending from the center of the primary particle surface to 1 / 4 of its radius corresponds to the surface and near-surface of the positive electrode active material, where side reactions are severe under high voltage. Conversely, the core region extending from the center of the primary particle to 1 / 4 of its radius corresponds to the bulk phase of the positive electrode active material, which is less prone to side reactions with the electrolyte. Therefore, controlling the coating of modified elements on the material surface to reduce the exposed surface (i.e., direct contact with the electrolyte) can directly reduce interfacial side reactions and significantly improve the cycle performance and storage life of secondary batteries.

[0050] When the average mass concentration of silicon in the outer region (corresponding to 1 / 4 radius from the center of the primary particle) of a lithium transition metal oxide primary particle is greater than that in the core region (corresponding to 1 / 4 radius from the center of the primary particle), it means that the silicon content in the outer region of the primary particle is higher than that in the core region. This means that silicon is more concentrated on the surface of the primary particle, forming a good coating layer that passivates the surface of the lithium transition metal oxide material. This provides a good physical barrier between the electrode and the electrolyte, reducing side reactions between the positive electrode active material and the electrolyte. This prevents damage to the material structure at high voltages (~4.5V), resulting in better high-temperature storage and cycle performance of the secondary battery. Furthermore, when the positive electrode active material also includes lithium transition metal phosphate, and... Lithium-containing transition metal phosphates include iron. When lithium-containing transition metal phosphates include secondary particles formed by the agglomeration of primary particles, the secondary particles have a smaller specific surface area and a particle size that is closer to that of lithium-containing transition metal oxides. This is more conducive to matching large-scale industrial processing without deteriorating the slurry processing performance. In addition, lithium-containing transition metal oxides have a rapid voltage drop at low SOC, while lithium-containing transition metal phosphates form a small plateau at low SOC. Therefore, by adding lithium-containing transition metal phosphates, the voltage drop in the low SOC segment becomes slower and more gradual, unlike the large voltage drop that occurs directly when using pure lithium-containing transition metal oxides. Thus, it is possible to slow down the voltage drop rate at low SOC, improve kinetic performance, and thereby improve the power performance of secondary batteries.

[0051] Therefore, the lithium-ion secondary battery of this application has both high power density and good cycle performance.

[0052] Lithium-containing transition metal oxides and lithium-containing transition metal phosphates can be distinguished by any means known to those skilled in the art, such as by SEM and / or EDS.

[0053] Whether lithium-containing transition metal phosphates include secondary particles formed by the agglomeration of primary particles can be determined by any means known to those skilled in the art, such as by SEM.

[0054] In this application, lithium-containing transition metal oxides are modified with Si, specifically through doping and / or coating. In some embodiments, the modification is in the form of coating.

[0055] In some embodiments, the porosity of the positive electrode sheet, as measured by ion polishing cross-sectional morphology analysis (CP), is 6%-10%.

[0056] When the porosity of the positive electrode sheet, as measured by ion polishing cross-sectional morphology analysis (CP), is 6%-10%, the high porosity improves the wettability of the electrolyte. The electrolyte provides an ion conduction pathway for the material, improving kinetic performance and thus enhancing the power performance of the lithium-ion secondary battery. Therefore, the lithium-ion secondary battery of this application exhibits a high power density.

[0057] In some embodiments, the porosity of the positive electrode, as measured by ion-polished cross-sectional morphology analysis (CP), is 7%-9%. In some embodiments, the porosity of the positive electrode, as measured by ion-polished cross-sectional morphology analysis (CP), is 6.5%-8.5%. In some embodiments, the porosity of the positive electrode, as measured by ion-polished cross-sectional morphology analysis (CP), is 7%-8.5%.

[0058] In some embodiments, the porosity of the positive electrode, as measured by ion polishing cross-sectional morphology analysis (CP), is 6%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9%, 9.5%, 10%, or a range of any two of the above values ​​or values ​​within that range.

[0059] When the porosity of the positive electrode sheet, as measured by ion polishing cross-sectional morphology analysis (CP), is 7%-9%, the lithium-ion secondary battery of this application has a high power density.

[0060] In some embodiments, the average mass concentration of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface of the lithium transition metal oxide is 0.1%-0.7%.

[0061] In some embodiments, the average mass concentration of silicon in the outer region corresponding to 1 / 4 radius extending from the surface of the primary particles containing lithium transition metal oxide is 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, or any two of the above values ​​or values ​​within that range.

[0062] In some embodiments, the average mass concentration of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface containing lithium transition metal oxide is 0.2%-0.5%.

[0063] When the average mass concentration of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface of the lithium transition metal oxide is 0.2%-0.5%, the lithium-ion secondary battery of this application has good cycle performance and high-temperature storage performance.

[0064] In some embodiments, the average mass concentration of silicon in the core region corresponding to 1 / 4 radius of the primary particle center of the lithium transition metal oxide is 0%-0.06%. In some embodiments, the average mass concentration of silicon in the core region corresponding to 1 / 4 radius of the primary particle center of the lithium transition metal oxide is 0%-0.03%.

[0065] In some embodiments, the average mass concentration of silicon in the core region corresponding to 1 / 4 radius of the primary particle center of the lithium transition metal oxide is 0.06%, 0.05%, 0.04%, 0.03%, 0.02%, 0.01%, 0%, or any range of two of the above values ​​or values ​​within that range.

[0066] In some embodiments, the average particle size of the primary particles containing lithium transition metal oxides is 1 μm to 5 μm. In some embodiments, the average particle size of the primary particles containing lithium transition metal oxides is 2 μm to 3 μm. In some embodiments, the average particle size of the primary particles containing lithium transition metal oxides is 1 μm to 3 μm. In some embodiments, the average particle size of the primary particles containing lithium transition metal oxides is 1.5 μm to 2.5 μm.

[0067] In some embodiments, the average particle size of the primary particles containing lithium transition metal oxides is 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, or 2.9 μm. 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm, 4.5μm, 4.6μm, 4.7μm, 4.8μm, 4.9μm, 5μm, or a range consisting of any two of the above values ​​or a value within that range.

[0068] In some embodiments, the volume average particle size Dv50 of the lithium-containing transition metal oxide is from 2 μm to 10 μm. In some embodiments, the volume average particle size Dv50 of the lithium-containing transition metal oxide is from 3 μm to 6 μm.

[0069] In some embodiments, the volume average particle size Dv50 of the lithium transition metal oxide is 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 4.6 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or a range of any two of the above values ​​or a value within that range.

[0070] In some embodiments, the average particle size of the primary particles containing lithium transition metal phosphate is from 10 nm to 1000 nm. In some embodiments, the average particle size of the primary particles containing lithium transition metal phosphate is from 50 nm to 500 nm. In some embodiments, the average particle size of the primary particles containing lithium transition metal phosphate is from 100 nm to 300 nm.

[0071] In some embodiments, the average particle size of the primary particles containing lithium transition metal phosphate is 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 230nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm, 1000nm, or a range of any two of the above values ​​or a value within that range.

[0072] Lithium-containing transition metal phosphates have primary particles at the nanoscale, with a small average particle size, resulting in shorter lithium-ion transport paths, faster transport speeds, and better kinetic performance. Incorporating such lithium-containing transition metal phosphates into cathode active materials enhances the power performance of secondary batteries. Furthermore, lithium-containing transition metal phosphates are relatively inexpensive, thus enabling cost reduction and making them more suitable for commercial production and applications.

[0073] In some embodiments, the average particle size of the primary particles containing lithium transition metal phosphate is 160 nm to 300 nm.

[0074] When the average particle size of the primary particles containing lithium transition metal phosphate is between 160 nm and 300 nm, the lithium-ion secondary battery of this application has good cycle performance and high-temperature storage performance.

[0075] In some embodiments, the average particle size of the primary particles containing lithium transition metal phosphate is 100 nm to 200 nm.

[0076] When the average particle size of the primary particles containing lithium transition metal phosphate is 100 nm to 200 nm, the lithium-ion secondary battery of this application has a high power density.

[0077] In some embodiments, the volume average particle size Dv50 of the lithium transition metal phosphate is 2 μm to 15 μm. In some embodiments, the volume average particle size Dv50 of the lithium transition metal phosphate is 6 μm to 15 μm. In some embodiments, the volume average particle size Dv50 of the lithium transition metal phosphate is 6.5 μm to 12 μm.

[0078] In some embodiments, the volume average particle size Dv50 of the lithium transition metal phosphate is 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 8.7 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, or a range of any two of the above values ​​or a value within that range.

[0079] In some embodiments, the volume average particle size Dv50 of the lithium transition metal phosphate is 2 μm to 10 μm.

[0080] In some embodiments, the specific surface area of ​​the lithium-containing transition metal phosphate is 2 m². 2 / g to 10m 2 / g. In some embodiments, the specific surface area of ​​the lithium-containing transition metal phosphate is 7m². 2 / g to 9.5m 2 / g. In some embodiments, the specific surface area of ​​the lithium-containing transition metal phosphate is 7m². 2 / g to 9m 2 / g.

[0081] In some embodiments, the specific surface area of ​​the lithium-containing transition metal phosphate is 2 m². 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g、5m 2 / g, 5.5m 2 / g、6m 2 / g, 6.5m 2 / g、7m 2 / g, 7.5m 2 / g、8m2 / g, 8.3m 2 / g, 8.5m 2 / g、9m 2 / g, 9.5m 2 / g, 10m 2 / g, or a range consisting of any two of the above values, or a value within that range.

[0082] In some embodiments, the lithium-containing transition metal phosphate has the molecular formula Li m1 Fe x Mn r P y O j1 Q1 q1 Q1 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.6 ≤ m1 ≤ 1.15, x > 0, r ≥ 0, 0.9 ≤ x + r ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j1 ≤ 4, and 0 ≤ q1 ≤ 0.1.

[0083] In some embodiments, the lithium-containing transition metal phosphate has the molecular formula Li m1 Fe x Mn r P y O j1 Q1 q1 Where m1 can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, or 1.15; x can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 1.0; and r can be 0, 0.05, or 0. 1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, y can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, j1 can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, q1 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1.

[0084] In some embodiments, the lithium-containing transition metal oxide has the molecular formula Li m2 (Ni a Co b Mn c ) 1-d Si d O j2 Q2q2 Q2 includes one or more of Zr, Ti, Nb, Al, P, Sr, W, B, Ba, Mg, Sn, Y, Na, S, N, F, Cl, Br and I, 0.6≤m2≤1.5, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1, 0<d≤0.1, 1.8≤j2≤2, 0≤q2≤0.2, j2+q2=2.

[0085] In some embodiments, the lithium-containing transition metal oxide has the molecular formula Li m2 (Ni a Co b Mn c ) 1-d Si d O j2 Q2 q2 Q2 includes one or more of Zr, Ti, Nb, Al, P, and F.

[0086] In some embodiments, the lithium-containing transition metal oxide has the molecular formula Li m2 (Ni a Co b Mn c ) 1-d Si d O j2 Q2 q2Where m2 can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, 1.18, 1.20, 1.23, 1.25, 1.28, 1.30, 1.33, 1.35, 1.38, or 1.40. 1.43, 1.45, 1.48, 1.50, where a can be 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, and b can be 0.02, 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, d can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, j2 can be 1.8, 1.81, 1.82, 1.83, 1.84, 1.85, 1.86, 1.87, 1.88, 1.89, 1.9, 1.91, 1.92, 1.93, 1.9 4, 1.95, 1.96, 1.97, 1.98, 1.99, 2, where q2 can be 0, 0.01, 0.02, 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, 0.2.

[0087] In some embodiments, the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is from 2:1 to 50:1. In some embodiments, the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is from 2:1 to 40:1.

[0088] In some embodiments, the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 2 6:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, 35:1, 36:1, 37:1, 38:1, 39:1, 40:1, 41:1, 42:1, 43:1, 44:1, 45:1, 46:1, 47:1, 48:1, 49:1, 50:1, or a range consisting of any two of the above values ​​or values ​​within that range.

[0089] In some embodiments, the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is 2:1 to 9:1.

[0090] When the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is 2:1 to 9:1, the lithium-ion secondary battery of this application has a high power density.

[0091] In some embodiments, the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is from 9:1 to 30:1.

[0092] When the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is 9:1 to 30:1, the lithium-ion secondary battery of this application has good cycle performance and high-temperature storage performance.

[0093] A second aspect of this application provides an electrical device comprising the lithium-ion secondary battery described in the first aspect of this application.

[0094] In addition, the lithium-ion secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0095] In one embodiment of this application, a secondary battery is provided.

[0096] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0097] [Positive electrode plate]

[0098] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0099] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0100] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0102] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0104] [Negative electrode plate]

[0105] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0106] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0107] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0108] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0109] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0110] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0112] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0113] [Electrolytes]

[0114] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0115] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0116] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0117] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0118] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0119] [Isolation membrane]

[0120] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0121] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0122] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0123] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0124] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0125] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured secondary battery 5 as an example.

[0126] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0127] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0128] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0129] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0130] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0131] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0132] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0133] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0134] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0135] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0136] Example

[0137] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0138] I. Preparation Method

[0139] Example 1

[0140] (1) Preparation of the positive electrode sheet:

[0141] Nickel sulfate (NiSO4·6H2O), cobalt sulfate (CoSO4·7H2O), and manganese sulfate (MnSO4·H2O) were added to a continuous stirred tank reactor at a molar ratio of Ni:Co:Mn = 55:12:33. Deionized water was added to prepare a transition metal salt solution with a total molar concentration of 2 mol / L. 4 mol / L sodium hydroxide was added as a precipitant, and 0.4 mol / L ammonia was added as a complexing agent. The precursor Ni for the ternary cathode material was prepared by co-precipitation reaction at pH 11.2 for 24 h. 0.55 Co 0.12 Mn0.33 (OH)2.

[0142] First, weigh the above-mentioned precursor Ni according to the molar ratio of Li:(Ni+Co+Mn)=1.06:1. 0.55 Co 0.12 Mn 0.33 (OH)₂ and lithium carbonate (Li₂CO₃) were mixed with 2500 ppm SiO₂ in a high-speed mixer, then sintered at 500°C for 8 hours in a kiln. After cooling to room temperature, the mixture was mechanically ground by an air jet mill for 5 hours to obtain the final product, lithium-containing transition metal oxide. The average mass concentration of silicon (CONC - outer region) in the primary particles of the lithium-containing transition metal oxide extending from the surface to the center to the outer region (corresponding to 1 / 4 of the radius) was 0.21%, and the average mass concentration of silicon (CONC - core region) in the core region extending from the center to the surface to the outer region (corresponding to 1 / 4 of the radius) was 0.011%. The average particle size of the primary particles of the lithium-containing transition metal oxide was 2.2 μm, and the volume average particle size (Dv₅₀) was 4.6 μm.

[0143] Using ferric phosphate and lithium carbonate as raw materials, glucose and polyethylene glycol were added as carbon sources, with the carbon source accounting for 17% of the total raw material mass. The raw materials were mixed in a 3.85:1:1 ratio and wet-milled using water as a solvent. The resulting slurry was spray-dried and then sintered in a roller furnace at 760℃ for 24 hours, with nitrogen gas introduced during the sintering process. After natural cooling to a material temperature <80℃, the material was discharged to obtain calcined feedstock. The calcined feedstock was then subjected to air-jet crushing, sieving, demagnetization, and vacuum packaging. The classifier frequency of the air-jet crusher was controlled at 50Hz–10080Hz, and the induced draft fan frequency was controlled at 20Hz–5040Hz, resulting in primary particles with an average particle size of 180nm, a volume average particle size (Dv50) of 8.7μm, and a BET of 8.3μm. 2 / g of lithium-containing transition metal phosphates.

[0144] Lithium-containing transition metal oxide and lithium-containing transition metal phosphate were mixed uniformly at a mass ratio of 90:10 to obtain the positive electrode active material. This positive electrode active material, conductive carbon black (SP), and binder (PVDF) were then dispersed in solvent NMP at a mass ratio of 95:4:1 and mixed uniformly to obtain the positive electrode slurry. The positive electrode slurry was then coated using a double-sided, dual-control coating device at a rate of 0.24 g / 1540.25 mm. 2 The material is uniformly coated onto the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained. The porosity of the positive electrode sheet is 7.63%.

[0145] (2) Preparation of negative electrode sheet:

[0146] Graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 95:2:2:1. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was then mixed at a rate of 0.16 g / 1540.25 mm. 2 The coating is evenly applied to copper foil; after the copper foil is dried at room temperature, it is transferred to a 120℃ oven to dry for 1 hour, and then cooled, pressed, and cut to obtain the negative electrode sheet.

[0147] (3) Separating membrane:

[0148] A 12μm thick polypropylene separator membrane.

[0149] (4) Electrolyte:

[0150] 1 mol / L lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) + diethyl carbonate (DEC) + methyl ethyl carbonate (EMC) (20:20:60).

[0151] (5) Battery fabrication:

[0152] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to obtain a bare battery cell. The bare battery cell is then placed in an aluminum-plastic film, encapsulated, injected with electrolyte, formed, and tested for capacity to obtain a lithium-ion battery.

[0153] Examples 2-7

[0154] The main differences between Examples 2-7 and Example 1 are shown in Table 1.

[0155] Comparative Example 1

[0156] The main difference between Comparative Example 1 and Example 1 is that the positive electrode active material does not contain lithium-containing transition metal phosphates, and the porosity of the positive electrode sheet measured by ion polishing cross-sectional morphology analysis (CP) is 5.91%.

[0157] Comparative Example 2

[0158] Compared with Example 1, the main difference in Comparative Example 2 is that SiO2 was not used in the preparation of the lithium-containing transition metal oxide. As a result, the average mass concentration ratio of silicon element in the outer region corresponding to 1 / 4 radius from the surface of the primary particles of the lithium-containing transition metal oxide (CONC-outer) and the average mass concentration ratio of silicon element in the core region corresponding to 1 / 4 radius from the center of the primary particles (CONC-core) are both 0. The porosity of the positive electrode sheet measured by CP through ion polishing cross-sectional morphology analysis is 7.62%.

[0159] II. Testing Methods

[0160] 1. The average mass concentration percentage of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface of a lithium transition metal oxide.

[0161] Powder samples were prepared for electron microscopy (EMS) by resin embedding and ion polishing. Prior to testing, carbon spraying was performed to increase the material's conductivity. Particles with good flatness and polishing were selected, and electron probe microanalysis (EPMA) was performed by drawing a line along the center of each particle. This yielded the average mass concentration of silicon in the outer region corresponding to 1 / 4 of the radius of the primary lithium transition metal oxide particle surface.

[0162] 2. The average mass concentration percentage of silicon in the core region corresponding to 1 / 4 radius of the primary particle center of the lithium transition metal oxide.

[0163] Powder samples were prepared for electron microscopy (EMS) by resin embedding and ion polishing. Before testing, carbon spraying was performed to increase the conductivity of the material. Particles with good flatness and polishing were selected, and electron probe microanalysis (EPMA) was performed by drawing a line at the center of the particle. The average mass concentration of silicon in the core region corresponding to 1 / 4 of the radius of the primary lithium transition metal oxide particle was obtained.

[0164] 3. Average particle size of primary particles

[0165] The "LIBMAS Lithium-ion Battery Material Microscopic Intelligent Analysis System" software was used to automatically identify primary particles using AI, draw particle outlines, and obtain particle quantity, number, area, and maximum caliper diameter. 2000 particles were collected, and the average was calculated.

[0166] Average particle size in one measurement = Sum of the sizes (longest diameter) of all measured particles / Sum of the number of all measured particles.

[0167] 4. Volume average particle size Dv50

[0168] The Malvern 3000 (MasterSizer 3000) laser particle size analyzer was used, and the determination was performed according to the standard procedure GB / T19077-2016 / ISO 13320:2009. The specific test procedure is as follows: Take an appropriate amount of the sample to be tested, ensuring the sample concentration is 8% to 12% opacity, add 20 mL of deionized water, and simultaneously ultrasonicate for 5 minutes at a frequency of 53 kHz and a power of 120 W to ensure complete dispersion of the sample. Then, the sample was measured according to the standard GB / T19077-2016 / ISO 13320:2009.

[0169] 5. Specific surface area

[0170] The specific surface area and porosity analyzer was used for determination according to the standard procedure GB / T19587-2017 / ISO 9277:2010. The specific test procedure is as follows: An appropriate amount of sample was placed in a dedicated sample tube, heated, and evacuated under vacuum for 2 hours. After cooling to room temperature, the total weight was weighed, and the sample mass was obtained by subtracting the mass of the sample tube. The sample tube was then placed in the workstation, and the amount of gas adsorbed on the solid surface under different adsorption pressures was measured at a constant low temperature. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption capacity of the sample was calculated, thereby determining the specific surface area per unit mass of the solid sample.

[0171] 6. Porosity of the positive electrode sheet measured by CP was analyzed by ion polishing cross-sectional morphology.

[0172] The positive electrode sheet was cut into 6mm*6mm samples using ceramic scissors and attached to the sample stage, with the sample slightly protruding from the edge of the sample stage (<1mm). Cutting was performed at 7.5kV for 50 minutes. The morphology was captured at 1500x magnification using a field emission scanning electron microscope (FET), and the porosity was calculated using Avizo software.

[0173] Porosity = Pore area / Total area

[0174] 7. 30S 10% SOC power density

[0175] Place the battery in a constant temperature room at 25℃ and let it stand for 2 hours. Once the battery temperature remains at 25℃, perform the following tests: Charge the battery with a constant current of 1 / 3C to 4.5V, then continue charging with a constant voltage until the charging current is less than 0.05C, then stop. Pause for 30 minutes; discharge the battery with a constant current of 1 / 3C to 0.9C0 (C0 is the battery capacity), i.e., adjust to 10% SOC, and let it stand for 2 hours. Discharge the battery with a current of X1 A for 30 seconds, and record this step capacity as C1. Let it stand for 5 minutes, then recharge the battery with a current of 1 / 20C to recharge the C1 capacity. Discharge the battery with a current of X2 A for 30 seconds, and record this step capacity as C2. Let it stand for 5 minutes, then recharge the battery with a current of 1 / 20C to recharge the C2 capacity. Repeat the above steps until the final voltage is 2.8±0.05V. At this point, the current is Xn. Calculate the power density using this current.

[0176] Power density = Power (W) / Discharge capacity (Wh) = Discharge voltage (V) * Test current (A) / Discharge capacity (Wh)

[0177] 8. Cyclic performance

[0178] Place the battery in a 45℃ constant temperature chamber and let it stand for 2 hours. Once the battery temperature remains at 45℃, conduct a charge-discharge test. Charge the battery with a 1 / 3C constant current to 4.5V, then continue charging with a constant voltage until the charging current is less than 0.05C, then stop; pause for 30 minutes; discharge the battery with a 1 / 3C constant current to 2.8V; pause for 10 minutes. This constitutes one charge-discharge cycle. Repeat this process continuously until the battery capacity decreases to 80% of its initial value, and record the number of cycles.

[0179] 9. High-temperature storage performance

[0180] High-temperature storage performance was characterized by the capacity retention rate of the battery after 100 days of high-temperature storage. At 25°C, the battery was charged at a constant current rate of 1 / 3C to 4.5V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 30 minutes, it was discharged at a constant current rate of 1 / 3C to 2.8V, and the initial discharge capacity was measured. After resting for 30 minutes, the battery was charged at a constant current rate of 1 / 3C to 4.5V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. The fully charged battery was then stored in a 60°C oven for 100 days. The battery, after being stored at high temperature for 100 days, was removed and allowed to cool naturally to 25°C. It was then discharged at a constant current rate of 1 / 3C to 2.8V, charged at a constant current rate of 1 / 3C to 4.5V, charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged at a constant current rate of 1 / 3C to 2.8V. The discharge capacity of the battery after being stored at high temperature for 100 days was then measured.

[0181] Battery capacity retention rate (%) after 100 days of high-temperature storage = Discharge capacity after 100 days of high-temperature storage / Initial discharge capacity × 100%.

[0182] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0183] Lithium-ion batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The relevant parameters of the positive electrode active material and the positive electrode sheet are shown in Table 1, and the performance test results of the secondary battery are shown in Table 2.

[0184] Table 1: Relevant parameters of positive electrode active material and positive electrode sheet

[0185] Table 2: Performance Test Results of Secondary Batteries

[0186] Based on the above results, it can be seen that the secondary batteries in Examples 1-7 all include a positive electrode sheet, which includes a positive current collector and a positive electrode film layer disposed on the positive current collector and including a positive electrode active material. The positive electrode active material includes lithium-containing transition metal oxides and lithium-containing transition metal phosphates. The lithium-containing transition metal oxides include nickel, cobalt, manganese, and / or aluminum, as well as silicon. The average mass concentration of silicon in the outer region corresponding to 1 / 4 radius from the surface of the primary particles of the lithium-containing transition metal oxide is greater than the average mass concentration of silicon in the core region corresponding to 1 / 4 radius from the center of the primary particles. The lithium-containing transition metal phosphate includes iron and includes secondary particles formed by the agglomeration of primary particles. A comparison of Examples 1-7 with Comparative Examples 1-2 shows that the lithium-ion secondary batteries of this application have both high power density and good cycle performance.

[0187] The lithium-containing transition metal oxide from Example 1 was prepared into a positive electrode sheet according to the method described in the example. After ion polishing, the sheet was observed using a field emission microscope (Zeiss Sigma 300). The morphology of the ion-polished cross-section is shown in Figure 7. The lithium-containing transition metal oxide from Example 1 was mixed with a lithium-containing transition metal phosphate and prepared into a positive electrode sheet according to the method described in the example. After ion polishing, the sheet was observed using a field emission microscope (Zeiss Sigma 300). The morphology of the ion-polished cross-section is shown in Figure 8.

[0188] As can be seen from the comparison between Examples 1-5, 7 and Example 6, when the porosity of the positive electrode sheet is 7%-9% as measured by ion polishing cross-sectional morphology analysis (CP), the secondary battery of this application embodiment has a high power density.

[0189] As can be seen from the comparison between Examples 1 and 3 and Example 2, when the average mass concentration of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface containing lithium transition metal oxide is 0.2%-0.5%, the lithium-ion secondary battery of this application embodiment has good cycle performance and high-temperature storage performance.

[0190] As can be seen from the comparison between Examples 1 and 5 and Example 4, when the average particle size of the primary particles containing lithium transition metal phosphate is 160 nm to 300 nm, the lithium-ion secondary battery of this application has good cycle performance and high-temperature storage performance.

[0191] As can be seen from the comparison between Examples 1-4 and Example 5, when the average particle size of the primary particles containing lithium transition metal phosphate is 100nm to 200nm, the lithium-ion secondary battery of this application embodiment has a high power density.

[0192] As can be seen from the comparison between Examples 1 and 7 and Example 6, when the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is 2:1 to 9:1, the lithium-ion secondary battery of this application embodiment has a high power density.

[0193] As can be seen from the comparison of Examples 1, 6 and 7, when the mass ratio of lithium-containing transition metal oxide to lithium-containing transition metal phosphate is 9:1 to 30:1, the lithium-ion secondary battery of this application has good cycle performance and high-temperature storage performance.

[0194] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium-ion secondary battery, characterized in that, The lithium-ion secondary battery includes a positive electrode. The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on the positive current collector and including a positive active material, wherein... The positive electrode active material includes lithium-containing transition metal oxides and lithium-containing transition metal phosphates. The lithium-containing transition metal oxide includes nickel, cobalt, manganese, and / or aluminum, as well as silicon. The average mass concentration of silicon in the outer region corresponding to 1 / 4 radius from the surface of the primary particle of the lithium-containing transition metal oxide is greater than the average mass concentration of silicon in the core region corresponding to 1 / 4 radius from the center of the primary particle. The lithium-containing transition metal phosphate includes iron, and the lithium-containing transition metal phosphate includes secondary particles formed by the agglomeration of primary particles.

2. The lithium-ion secondary battery according to claim 1, wherein, The porosity of the positive electrode sheet, as determined by ion polishing cross-sectional morphology analysis (CP), is 6%-10%.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein, The porosity of the positive electrode sheet, as determined by ion polishing cross-sectional morphology analysis (CP), is 7%-9%.

4. The lithium-ion secondary battery according to any one of claims 1-3, wherein, The average mass concentration of silicon in the outer region corresponding to 1 / 4 radius of the primary particle surface of the lithium-containing transition metal oxide is 0.1%-0.7%.

5. The lithium-ion secondary battery according to any one of claims 1-4, wherein, The average mass concentration of silicon in the core region corresponding to 1 / 4 radius of the primary particle center of the lithium-containing transition metal oxide is 0%-0.06%.

6. The lithium-ion secondary battery according to any one of claims 1-5, wherein, The average particle size of the primary particles of the lithium-containing transition metal oxide is 1 μm to 5 μm.

7. The lithium-ion secondary battery according to any one of claims 1-6, wherein, The volume average particle size Dv50 of the lithium-containing transition metal oxide is 2 μm to 10 μm.

8. The lithium-ion secondary battery according to any one of claims 1-7, wherein, The volume average particle size Dv50 of the lithium-containing transition metal phosphate is 2 μm to 15 μm.

9. The lithium-ion secondary battery according to any one of claims 1-8, wherein, The specific surface area of ​​the lithium-containing transition metal phosphate is 2m². 2 / g to 10m 2 / g.

10. The lithium-ion secondary battery according to any one of claims 1-9, wherein, The lithium-containing transition metal phosphate has the molecular formula Li m1 Fe x Mn r P y O j1 Q1 q1 Q1 includes at least one of Al, Na, K, Mg, Cu, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.6 ≤ m1 ≤ 1.15, x > 0, r ≥ 0, 0.9 ≤ x + r ≤ 1, 0.95 ≤ y ≤ 1, 3.5 ≤ j1 ≤ 4, and 0 ≤ q1 ≤ 0.

1.

11. The lithium-ion secondary battery according to any one of claims 1-10, wherein, The lithium-containing transition metal oxide has the molecular formula Li m2 (Ni a Co b Mn c ) 1-d Si d O j2 Q2 q2 Q2 includes one or more of Zr, Ti, Nb, Al, P, Sr, W, B, Ba, Mg, Sn, Y, Na, S, N, F, Cl, Br and I, 0.6≤m2≤1.5, 0.3≤a≤0.7, 0.02≤b≤0.15, a+b+c=1, 0<d≤0.1, 1.8≤j2≤2, 0≤q2≤0.2, j2+q2=2.

12. The lithium-ion secondary battery according to any one of claims 1-11, wherein, The mass ratio of the lithium-containing transition metal oxide to the lithium-containing transition metal phosphate is from 2:1 to 50:

1.

13. An electrical device comprising a lithium-ion secondary battery as described in any one of claims 1-12.

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