A secondary battery and electrical device

Abstract

This application provides a secondary battery and an electrical device. The secondary battery includes a positive electrode sheet, which includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; the positive active layer includes a positive active material composition; the positive active material composition includes lithium transition metal phosphate and lithium nickel cobalt manganese oxide; the positive active layer satisfies: 0.10 ≤ [Ni 3+ ] / [Ni 4+ ]≤0.95, where, [Ni 3+ [] indicates the Ni in the positive electrode active layer in the XPS spectrum. 3+ The peak area of ​​[Ni] 4+ [] indicates the Ni in the positive electrode active layer in the XPS spectrum. 4+ The peak area of ​​Ni in the positive electrode active layer of this application. 3+ and Ni 4+ Within a specific range, the ratio can simultaneously improve the fast charging performance and energy density of secondary batteries.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] With the advancement of science and technology, lithium-ion batteries, as a highly efficient energy storage technology, are widely used in consumer electronics, electric vehicles, and large-scale energy storage devices. Simultaneously, the requirements for lithium-ion batteries are becoming increasingly stringent, particularly regarding their fast-charging performance and cycle life. However, during fast charging, the rapid migration of lithium ions can easily lead to localized overheating due to intensified polarization, damaging the structure of the electrode active materials. Furthermore, the lithium-ion insertion rate lags behind the migration rate, easily causing lithium dendrites to precipitate at the negative electrode, piercing the separator and consuming active materials. In addition, high current can accelerate electrolyte decomposition and disrupt the stability of the SEI film on the electrode surface. These accumulated damages ultimately lead to a decrease in cycle life.

[0003] Therefore, there is a need to develop a rechargeable battery that combines fast charging and long cycle life. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery that combines fast charging and long cycle life.

[0005] To achieve the above objectives, a first aspect of this application provides a secondary battery, the secondary battery comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; the positive active layer comprising a positive active material composition; The positive electrode active material composition includes lithium transition metal phosphate and lithium nickel cobalt manganese oxide; The positive electrode active layer satisfies: 0.10 ≤ [Ni 3+ ] / [Ni 4+ ]≤0.95, where, [Ni 3+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 3+ The peak area of ​​[Ni] 4+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 4+ The peak area.

[0006] As an embodiment of this application, the positive electrode active material layer further includes a lithium replenishing agent, which includes lithium-rich nickel oxide.

[0007] As an embodiment of this application, the mass ratio of the lithium-rich nickel oxide and the positive electrode active material composition is A, which satisfies: 0.01≤A≤0.12.

[0008] As an embodiment of this application, the mass ratio of the lithium-rich nickel oxide to the lithium nickel cobalt manganese oxide is 1:(1~5).

[0009] As an embodiment of this application, the general structural formula of the lithium-rich nickel oxide is Li X NiO2, 1≤x≤2.

[0010] As an embodiment of this application, the general structural formula of the lithium nickel cobalt manganese oxide is Li a Ni b Co c Mn d M e O2, wherein 0.9≤a≤1.1, 0<b<1, 0<c<1, 0<d<1, 0≤e≤0.3, b+c+d+e=1, and M is selected from at least one element from Y, Ti, Na, Fe, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, and V.

[0011] As an embodiment of this application, the lithium transition metal phosphate includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

[0012] As an embodiment of this application, the positive electrode active material composition satisfies: 2.0≤T=(Dv90-Dv10) / Dv50≤3.1, where Dv10 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material composition reaching 10%, in μm; Dv50 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material composition reaching 50%, in μm; and Dv90 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material composition reaching 90%, in μm.

[0013] As an embodiment of this application, the positive electrode active material composition satisfies: 0.3μm≤Dv10≤1μm.

[0014] As an embodiment of this application, the positive electrode active material composition satisfies: 1μm≤Dv50≤3μm.

[0015] As an embodiment of this application, the positive electrode active material composition satisfies: 2μm≤Dv90≤7μm.

[0016] As an embodiment of this application, the secondary battery further includes a negative electrode sheet, the negative electrode sheet including a negative current collector, and a first negative active layer and a second negative active layer disposed on at least one side surface of the negative current collector, the first negative active layer being disposed between the negative current collector and the second negative active layer; the porosity of the first negative active layer is P1%, the porosity of the second negative active layer is P2%, and P1 < P2.

[0017] As an embodiment of this application, the porosity of the first negative electrode active layer satisfies: 25%≤P1%≤35%.

[0018] As an embodiment of this application, the porosity of the second negative electrode active layer satisfies: 30%≤P2%≤45%.

[0019] As an embodiment of this application, the first negative electrode active layer includes a first negative electrode active material, which comprises a first graphite and a silicon-based material, wherein the median particle size of the first graphite is [missing information]. 1 Dv50; The second negative electrode active layer contains a second negative electrode active material, which includes a second graphite, the median particle size of which is... 2 Dv50; satisfies: 1 Dv50> 2 Dv50; where, 1 Dv50 represents the particle size corresponding to when the cumulative volume percentage of the first graphite reaches 50%, in μm; 2 Dv50 represents the particle size corresponding to when the cumulative volume percentage of the second graphite reaches 50%, in μm.

[0020] As an embodiment of this application, the median particle size of the first graphite 1 Dv50 satisfies: 13μm≤ 1 Dv50≤17μm.

[0021] As an embodiment of this application, the median particle size of the second graphite 2 Dv50 satisfies: 10μm≤ 2 Dv50≤14μm.

[0022] As an embodiment of this application, the mass percentage of the silicon-based material is 1% to 10% based on the total mass of the first negative electrode active material.

[0023] As an embodiment of this application, the silicon-based material includes a silicon oxide compound, wherein the median particle size of the silicon oxide compound is... 3 Dv50 is 1~3μm. 3 Dv50 represents the particle size corresponding to a cumulative volume percentage of 50% for the silicon oxide compound.

[0024] A second aspect of this application also provides an electrical device, the electrical device comprising the secondary battery described in the first aspect of this application.

[0025] Compared with the prior art, the beneficial effects of this application are: The positive electrode active layer of this application satisfies: 0.10 ≤ [Ni 3+ ] / [Ni4+ The concentration of lithium ions is ≤0.95, which allows some lithium ions to participate in the formation of the SEI film on the negative electrode during the battery cycle, thus compensating for the initial efficiency. The other part is pre-existing in the negative electrode as active lithium. The active lithium pre-existing in the negative electrode can be slowly released during subsequent cycles to improve the cycle and storage life of the secondary battery, as well as to improve the energy density. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0028] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] A first aspect of this application provides a secondary battery, the secondary battery including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; the positive active layer includes a positive active material composition; The positive electrode active material composition includes lithium transition metal phosphate and lithium nickel cobalt manganese oxide; The positive electrode active layer satisfies: 0.10 ≤ [Ni 3+ ] / [Ni 4+ ]≤0.95, where, [Ni 3+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 3+ The peak area of ​​[Ni] 4+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 4+ The peak area.

[0030] Ni in the positive electrode active layer of this application 3+ and Ni 4+When the peak area ratio in the XPS spectrum is within a suitable range, a redox reaction will occur inside the cathode material composition, thereby slowly releasing lithium ions from the cathode active material layer. Some of the lithium ions will participate in the formation of the anode SEI film, which can compensate for the initial efficiency; the other part will be pre-existing in the anode as active lithium. The active lithium pre-existing in the anode can be slowly released during subsequent cycles, improving the cycle and storage life of the secondary battery and simultaneously increasing the energy density.

[0031] In some embodiments of this application, the positive electrode active material layer further includes a lithium replenishing agent, which includes lithium-rich nickel oxide. The lithium replenishing agent can further replenish lithium ions, thereby optimizing the battery's initial efficiency and cycle life.

[0032] In some embodiments of this application, the mass ratio A of the lithium-rich nickel oxide and the positive electrode active material composition satisfies: 0.01 ≤ A ≤ 0.12. Maintaining this suitable mass ratio within this range allows for further improvement of the cycle life of the secondary battery while preserving its high energy density. Specifically, A can be any value from 0.01, 0.05, 0.11, and 0.12, or any value within the range formed by any two of the aforementioned values.

[0033] In some embodiments of this application, the mass ratio of the lithium-rich nickel oxide to the lithium nickel cobalt manganese oxide is 1:(1~5). A mass ratio of lithium-rich nickel oxide to lithium nickel cobalt manganese oxide within the aforementioned suitable range is beneficial for improving the lithium replenishment effect, thereby increasing the energy density of the secondary battery, and also for improving the cycle life of the secondary battery. Specifically, the mass ratio of lithium-rich nickel oxide to lithium nickel cobalt manganese oxide can be any ratio selected from 1:1, 1:3, and 1:5, or fall within the range formed by any two of the aforementioned ratios.

[0034] In some embodiments of this application, the general structural formula of the lithium-rich nickel oxide is Li. X For NiO2, 1 ≤ x ≤ 2. This can improve the lithium replenishment effect.

[0035] In some embodiments of this application, the mass percentage of lithium transition metal phosphate in the positive electrode active material composition is 2% to 98%; In some embodiments of this application, the mass percentage of lithium transition metal phosphate in the positive electrode active material composition is 30% to 96%; In some embodiments of this application, the mass percentage of lithium transition metal phosphate in the positive electrode active material composition is 70% to 94%.

[0036] In some embodiments of this application, the general structural formula of the lithium nickel cobalt manganese oxide is Li a Nib Co c Mn d M e O2, where 0.9≤a≤1.1, 0<b<1, 0<c<1, 0<d<1, 0≤e≤0.3, b+c+d+e=1, and M represents the doping element, which is selected from at least one element from Y, Ti, Na, Fe, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, and V. This can improve the energy density of the battery.

[0037] In some embodiments of this application, the lithium transition metal phosphate includes at least one of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP). This can improve the cycle life of the battery.

[0038] In some embodiments of this application, the positive electrode active material composition satisfies: 2.0 ≤ T = (Dv90 - Dv10) / Dv50 ≤ 3.1, where Dv10 is the particle size corresponding to a cumulative volume percentage of 10% of the positive electrode active material composition, in μm; Dv50 is the particle size corresponding to a cumulative volume percentage of 50% of the positive electrode active material composition, in μm; and Dv90 is the particle size corresponding to a cumulative volume percentage of 90% of the positive electrode active material composition, in μm. By designing the size of the positive electrode active material composition, the particle size of the positive electrode active material composition satisfies this relationship range, indicating that the volume distribution ratio of large particles in the positive electrode active material composition is relatively high. This can slow down the lithium-ion insertion / extraction rate of lithium transition metal phosphate, achieving a slow release of lithium ions, and further improving the cycle and storage life of the secondary battery. The value of T can be any one of 1.7, 2.0, 2.8, 3.1, 3.7, or any value within the range formed by any two of the above values.

[0039] In some embodiments of this application, the positive electrode active material composition satisfies the following condition: 0.3 μm ≤ Dv10 ≤ 1 μm. Specifically, the value of Dv10 of the positive electrode active material composition can be any one of 0.3 μm, 0.4 μm, 0.5 μm, 0.8 μm, and 1 μm, or any value within the range formed by any two of the above values.

[0040] In some embodiments of this application, the positive electrode active material composition satisfies: 1μm≤Dv50≤3μm. Specifically, the Dv50 value of the positive electrode active material composition can be any one of 1μm, 1.2μm, 1.6μm, 1.8μm, 2μm, and 3μm, or any value within the range formed by any two of the above values.

[0041] In some embodiments of this application, the positive electrode active material composition satisfies: 2μm≤Dv90≤7μm. Specifically, the Dv10 value of the positive electrode active material composition can be any one of 2μm, 4.6μm, 4.8μm, 5.5μm, 6μm, 6.4μm, and 7μm, or any value within the range formed by any two of the above values.

[0042] In some embodiments of this application, the positive electrode active layer further includes a conductive agent, a binder, and a dispersant. This application does not specifically limit the types of conductive agents, binders, and dispersants in the positive electrode active layer. Commonly used positive electrode conductive agents, binders, and dispersants in the art can all be used in this application to prepare the positive electrode active layer. For example, the conductive agent may be at least one of carbon black, graphene, carbon nanotubes (CNT), and acetylene black (ACET), including but not limited to the listed conductive agents; the binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), 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), including but not limited to the listed binders; the dispersant includes, but is not limited to, polyvinylpyrrolidone (PVP).

[0043] In some embodiments of this application, the thickness of the positive electrode active layer is 170~220μm, specifically any value among 170μm, 190μm, and 220μm, or any value within the range formed by any two of the above values.

[0044] In some embodiments of this application, the compaction density of the positive electrode active layer is 2.4~2.6 g / cm³. 3 Specifically, it could be 2.4 g / cm³ 3 2.5g / cm 3 2.6g / cm 3 The value can be any one of the values ​​in the range or any value within the range formed by any two of the above values. A compaction density within this range is beneficial for electrolyte wetting and shortens the migration path of lithium ions in the positive electrode, thereby improving the fast-charging performance and energy density of the secondary battery.

[0045] In some embodiments of this application, the porosity of the positive electrode active layer is 25-45%, specifically any value from 25%, 26%, 27%, 28%, 29%, 30%, 33%, and 45%, or any value within the range formed by any two of the above values. A porosity within this range is beneficial for electrolyte wetting, ensuring uniform electrolyte distribution within the positive electrode sheet to reduce localized side reactions. It also allows for sufficient reaction of the positive electrode active material composition, slowing down the battery capacity decay rate and improving the cycle life and storage life of the secondary battery.

[0046] In some embodiments of this application, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a first negative active layer and a second negative active layer disposed on at least one side surface of the negative current collector. The first negative active layer is disposed between the negative current collector and the second negative active layer. The porosity of the first negative active layer is P1%, and the porosity of the second negative active layer is P2%, where P1 < P2. The second negative active layer is located on the surface of the negative electrode sheet. A larger porosity can increase the number of active sites on the surface of the negative electrode sheet. More active sites can improve the charge exchange rate between active ions and electrons in the secondary battery, thereby improving the fast-charging performance of the secondary battery. The first negative electrode active layer is located at the bottom of the negative electrode sheet. Compared with the second negative electrode active layer, the first negative electrode active layer has a smaller porosity. This relatively dense structure can not only accommodate more negative electrode active material to improve the energy density of the secondary battery, but also improve the peel force between the second negative electrode active layer and the negative electrode current collector, preventing the negative electrode active layers (including the first and second negative electrode active layers) from falling off the negative electrode current collector during the cycle and storage of the secondary battery, thereby improving the cycle and storage life of the secondary battery. With the P1 < P2 setting, the porosity of the negative electrode sheet increases gradually from the side closer to the current collector to the side farther away from the current collector in the thickness direction of the negative electrode sheet. This gradient porosity can improve the wettability of the negative electrode sheet in the electrolyte, allowing the negative electrode sheet to adsorb more active lithium and pre-store the active lithium in the second negative electrode active layer with relatively low porosity on the negative electrode sheet, so that it can be slowly released during subsequent cycles, further improving the cycle life of the secondary battery.

[0047] In some embodiments of this application, the porosity P1% of the first negative electrode active layer satisfies: 25%≤P1%≤35%. The specific value of the porosity P1% of the first negative electrode active layer can be any one of 25%, 28%, 30%, 31%, 32%, 33%, 35%, or any value within the range formed by any two of the above values.

[0048] In some embodiments of this application, the porosity P2% of the second negative electrode active layer satisfies: 30% ≤ P2% ≤ 45%. The specific value of the porosity P2% of the second negative electrode active layer can be any one of 30%, 40%, 42%, 45%, or any value within the range formed by any two of the above values.

[0049] In this application, the porosity of the positive electrode active layer, the porosity P1% of the first negative electrode active layer, and the porosity P2% of the second negative electrode active layer are obtained by testing using a "cross-sectional imaging combined with image analysis method". Specifically, the electrode sheet is first brittle-broken with liquid nitrogen or cut with FIB to obtain a flat cross-section. Then, the cross-section is treated with gold / carbon spraying to enhance conductivity. The upper and lower layer structures are observed using SEM / FIB-SEM at low magnification (500×) and high magnification (10000×), respectively. Finally, imageJ, Fiji and other software are used for binarization to distinguish pores from the substrate, and the porosity can be calculated.

[0050] In some embodiments of this application, the first negative electrode active layer includes a first negative electrode active material, which comprises a first graphite and a silicon-based material, wherein the median particle size of the first graphite is [missing information]. 1 Dv50; The second negative electrode active layer contains a second negative electrode active material, which includes a second graphite, the median particle size of which is... 2 Dv50; satisfies: 1 Dv50> 2 Dv50; where, 1 Dv50 represents the particle size corresponding to when the cumulative volume percentage of the first graphite reaches 50%, in μm; 2 Dv50 represents the particle size corresponding to a cumulative volume percentage of 50% for the second graphite, expressed in μm. The second negative electrode active layer contains second graphite with a smaller median particle size, which helps to reduce the impedance of the negative electrode surface. The first negative electrode active layer contains first graphite with a larger median particle size, which has stronger structural stability and a relatively lower volume expansion rate during lithium intercalation, thus helping to alleviate electrode cracking, improve the structural stability of the negative electrode, and enhance the cycle life of the secondary battery.

[0051] In some embodiments of this application, the median particle size of the first graphite 1 Dv50 satisfies: 13μm≤ 1 Dv50 ≤ 17μm. The median particle size of the first graphite is within the aforementioned suitable range, enabling the secondary battery to possess both long cycle life and fast-charging performance. Median particle size of the first graphite. 1The specific value of Dv50 can be any one of 13μm, 15μm, and 17μm, or any value within the range formed by any two of the above values.

[0052] In some embodiments of this application, the median particle size of the second graphite 2 Dv50 satisfies: 10μm≤ 2 Dv50 ≤ 14μm. The median particle size of the first type of graphite, within the aforementioned suitable range, enables the secondary battery to possess both long cycle life and fast-charging performance. The median particle size of the second type of graphite... 2 The specific value of Dv50 can be any one of 10μm, 12μm, 14μm, or any value within the range formed by any two of the above values.

[0053] In some embodiments of this application, the mass percentage of the silicon-based material is 1% to 10% based on the total mass of the first negative electrode active material. Specifically, the mass percentage of the silicon-based material can be any one of 1%, 5%, or 10%, or any value within the range formed by any two of the above values.

[0054] In some embodiments of this application, the silicon-based material comprises a silicon oxide compound, and the median particle size of the silicon oxide compound is... 3 Dv50 is 1~3μm. 3 Dv50 represents the particle size corresponding to a cumulative volume percentage of 50% for the silicon oxide compound. The median particle size of the silicon oxide compound. 3 The value of Dv50 can be any one of 1μm, 2μm, and 3μm, or any value within the range formed by any two of the above values. The silicon oxide compound includes, but is not limited to, at least one of SiO2 and SiO.

[0055] The first negative electrode active layer of this application comprises relatively large-particle-size first graphite and small-particle-size silicon-based material. The addition of the first graphite contributes to the cycle stability of the negative electrode active layer, while the small-particle-size silicon-based material fills the gaps in the first graphite, reducing the porosity of the first negative electrode active layer and further improving the energy density of the secondary battery. When the mass ratio of the first graphite to the silicon-based material is within a suitable range, the energy density and cycle life of the secondary battery can be further improved.

[0056] In some embodiments of this application, the thickness of the first negative electrode active layer is 64~90μm, specifically any value among 64μm, 65μm, 72μm, 83μm, and 90μm, or any value within the range formed by any two of the above values.

[0057] In some embodiments of this application, the thickness of the second negative electrode active layer is 64~90μm, specifically any value among 64μm, 65μm, 72μm, 83μm, and 90μm, or any value within the range formed by any two of the above values.

[0058] In some embodiments of this application, the compaction density of the first negative electrode active layer is 1.4~1.6 g / cm³. 3 Specifically, it could be 1.4 g / cm³ 3 1.6g / cm 3 It can be any value in the range or any value within the interval formed by any two of the above values.

[0059] In some embodiments of this application, the compaction density of the second negative electrode active layer is 1.4~1.6 g / cm³. 3 Specifically, it could be 1.4 g / cm³. 3 1.6g / cm 3 It can be any value in the range or any value within the interval formed by any two of the above values.

[0060] In some embodiments of this application, the peel force between the first negative electrode active layer and the negative electrode current collector is FN / m, where 10N / m ≤ FN / m ≤ 80N / m. Specifically, it can be any value among 10N / m, 30N / m, 40N / m, 48N / m, 50N / m, 55N / m, 60N / m, and 80N / m, or any value within the range formed by any two of the above values.

[0061] In some embodiments of this application, the first and second negative electrode active layers may also independently include conductive agents, binders, and thickeners, depending on performance requirements. This application does not specifically limit the types of conductive agents, binders, and thickeners in the negative electrode active layer; commonly used negative electrode conductive agents, binders, and thickeners in the art can all be used to prepare the negative electrode active layer in this application. For example, the conductive agent may be at least one of carbon black, graphene, carbon nanotubes, and acetylene black, including but not limited to the listed conductive agents; the thickener may include but is not limited to sodium carboxymethyl cellulose (CMC); and the binder may include but is not limited to polyacrylic acid (PAA).

[0062] In some embodiments of this application, there are no restrictions on the type of solvent used to form the positive electrode slurry and / or negative electrode slurry, as long as it is a solvent that can dissolve or disperse the positive electrode active material, the negative electrode active material, the conductive agent, the binder, or the thickener.

[0063] Commonly used positive and negative current collectors in this field can be used to prepare the secondary battery described in this application. The negative current collector can be copper foil or carbon-coated copper foil. The positive current collector can be made of metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; or composite materials formed by polymers and metal layers. In some embodiments of this application, carbon-coated aluminum foil is used as the positive current collector.

[0064] In some embodiments of this application, the electrolyte includes lithium salts and organic solvents, and may also contain additives. The types and compositions of the lithium salts and organic solvents are not particularly limited and can be selected according to actual needs. The lithium salts may include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, etc.; the organic solvents may include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propyl propionate, etc.; and the additives may include lithium difluorophosphate, lithium bis(oxalato)borate, succinate, 1,3-propanesulfonyl lactone, and ethylene sulfate, etc.

[0065] In this application, the type of diaphragm is not particularly limited and can be selected according to actual needs. The diaphragm can be a polypropylene membrane, a polyethylene membrane, a polyvinylidene fluoride membrane, a spandex membrane, an aramid membrane, or a multilayer composite membrane modified with a coating.

[0066] In some embodiments of this application, the preparation of the secondary battery includes: stacking the positive electrode, separator, and negative electrode in sequence, so that the separator is positioned between the positive and negative electrode to act as a separator, then winding it into a square bare cell, installing it into a battery casing, then baking it at 65~95°C to remove water, injecting electrolyte, sealing it, and then undergoing processes such as standing, hot and cold pressing, formation, clamping, and capacity testing to obtain the secondary battery.

[0067] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft pack, such as a pouch-type soft pack. The soft pack may be made of plastic, such as one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, or an aluminum-plastic film, such as an aluminum-plastic film formed by a composite of a PA layer, an aluminum layer, and a PP layer. The shape of the secondary battery is not particularly limited; it may be cylindrical, square, or any other arbitrary shape.

[0068] In some embodiments of this application, the secondary battery satisfies: 40≤Z=0.8×A×T+2×(1-P)×F≤80 T=(Dv90-Dv10) / Dv50 Wherein, A represents the mass ratio of the lithium-rich nickel oxide to the positive electrode active material composition; Dv10 represents the particle size corresponding to a cumulative volume percentage of 10% for the positive electrode active material composition, in μm. Dv50 represents the particle size corresponding to a cumulative volume percentage of 50% for the positive electrode active material composition, in μm. Dv90 represents the particle size corresponding to a cumulative volume percentage of 90% for the positive electrode active material composition, in μm. P represents the porosity of the negative electrode active layer, in %; the negative electrode active layer includes a first negative electrode active layer and a second negative electrode active layer. F represents the peeling force between the first negative electrode active layer and the negative electrode current collector, in N / m.

[0069] The secondary battery of this application satisfies the above relationship, which can further improve the fast charging performance of the secondary battery (especially reduce the fast charging DCR growth rate) and energy density.

[0070] A second aspect of this application provides an electrical device comprising the secondary battery described in the first aspect of this application. The electrical device can be an application device such as a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool. Vehicles can be new energy vehicles, including pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles; spacecraft include airplanes, rockets, space shuttles, and spacecraft; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. This application does not impose special limitations on the above-described device.

[0071] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0072] Examples 1-14, Comparative Examples 1-3 Example 1: A series of secondary batteries are provided, and the preparation method includes the following steps: Preparation of positive electrode sheet Lithium-containing active particles, conductive agent acetylene black (ACET), binder PVDF, and dispersant PVP were mixed evenly in a mass ratio of 95:2:1.5:1.5, and then uniformly dispersed in the solvent 1-methyl-2-pyrrolidone (NMP) to prepare a uniform black positive electrode slurry (solid content of 62wt%). The mixed positive electrode slurry was coated on one side with a surface density of σ=218g / m². 2 After coating both sides of the positive electrode current collector aluminum foil, the material is baked, rolled, and cut into sheets to obtain the positive electrode sheet. The thickness of the positive electrode active layer on the positive electrode sheet is 190 μm, and the compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 ; Among them, lithium-containing active particles include lithium transition metal phosphates, lithium nickel cobalt manganese oxides and lithium-rich nickel oxides. For details on the specific types, particle size parameters and dosage ratios, please refer to Table 1. Preparation of negative electrode sheet The first negative electrode active material (see Table 2), binder PVDF, dispersant (PVP), conductive agent (CNT), and thickener (CMC) were mixed at a mass ratio of 96:1.0:1.0:1.7:0.3 to obtain a mixed slurry, which was used as the first negative electrode active layer slurry. The second negative electrode active material (see Table 2), binder (PVDF), dispersant (PVP), and conductive agent (CNT) were mixed at a mass ratio of 96.5:2:0.5:1 to obtain a mixed slurry, which was used as the second negative electrode active layer slurry. A double-layer coating method is used, with the first negative electrode active layer slurry (single-sided coating surface density of 0.005 g / cm³) applied. 2 The second negative electrode active layer slurry (single-sided coating surface density of 0.005 g / cm³) 2 The coating is applied to both sides of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain the negative electrode sheet. In the obtained negative electrode sheet: the thickness of the first negative electrode active layer is 64 μm and the compaction density is 1.6 g / cm³. 3 The porosity is shown in Table 2. The thickness of the second negative electrode active layer is 64 μm and the compaction density is 1.6 g / cm³. 3 Porosity is shown in Table 2; Preparation of electrolyte At room temperature (25°C), in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), EC and EMC were mixed uniformly at a mass ratio of 3:7. Water was removed using a 4 Å molecular sieve to obtain a mixed solvent. 12.5 wt% (based on the total mass of the electrolyte) of lithium salt LiPF6 was added to the mixed solvent. The mixture was stirred continuously and cooled with dry ice to ensure that the electrolyte temperature rise did not exceed 2°C. Finally, a colorless and transparent liquid was obtained, which is the electrolyte. Assemble secondary batteries The prepared positive electrode sheet, separator (10μm thick PE base film), and negative electrode sheet are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. After winding, hot pressing and shaping, and electrode tab welding, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 90±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery. After top and side sealing, electrolyte injection, formation and capacity testing, a secondary battery can be obtained. The above-mentioned capacity allocation steps are as follows: 1) After formation, let the battery cell stand for 10 minutes. 2) Then charge at a constant current of 0.5C for 60 minutes, then charge at a constant current of 0.3C until 3.65V is cut off, then charge at a constant current and voltage of 0.1C until 4.25V is cut off, and finally charge at a current of 0.01C. 3) After charging is complete, let it stand for 3 minutes, then discharge it at a constant current of 0.33C until it cuts off at 2.5V.

[0073] Examples 2-14 The secondary battery is provided, and the preparation method is basically the same as that of the comparative example. The difference is that the parameters of the preparation process are adjusted, and the specific adjustments are shown in Table 1.

[0074] Comparative Examples 1-3 The secondary battery is provided, and the preparation method is basically the same as that of the comparative examples, except that the parameters of the preparation process are adjusted, as shown in Table 1. In addition to adjusting the parameters of the positive and negative electrode preparation processes, comparative examples 1-3 also adjusted the parameters of the battery capacity testing process, specifically: Comparative Example 1 Battery Capacity Testing Step 2) is as follows: First, charge at a constant current of 0.5C for 60 minutes, then charge at a constant current of 0.3C until 3.65V is cut off, then charge at a constant current and voltage of 0.1C until 3.8V is cut off, and finally charge at a current of 0.01C is cut off.

[0075] Comparative Example 2 Battery Capacity Testing Step 2) is as follows: First, charge at a constant current of 0.5C for 60 minutes, then charge at a constant current of 0.3C until 3.65V is cut off, then charge at a constant current and voltage of 0.1C until 4.3V is achieved, and finally charge at a current of 0.01C until the charging is cut off.

[0076] Comparative Example 3 Battery Capacity Testing Step 2) is as follows: First, charge at a constant current of 0.5C for 60 minutes, then charge at a constant current of 0.3C until 3.65V is cut off, then charge at a constant current and voltage of 0.1C until 4.35V is achieved, and finally charge at a current of 0.01C until the charging is cut off.

[0077] Table 1 Parameters of the positive electrode active layer It should be noted that in Table 1: (1) The particle size (Dv10, Dv50, Dv90) of the positive electrode active material composition was obtained by particle size analyzer; (2) T=(Dv90-Dv10) / Dv50; (3) A represents the mass ratio of lithium-rich nickel oxide to the positive electrode active material composition; (4) [Ni 3+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 3+ The peak area of ​​[Ni] 4+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 4+ The peak area; (5) The porosity of the positive electrode active layer was obtained by cross-sectional imaging combined with image analysis. Specifically, the positive electrode sheet was first brittlely broken with liquid nitrogen to obtain a flat cross-section. Then, the cross-section was sputtered with gold to enhance conductivity. The structure of the positive electrode active layer was observed by SEM at low magnification (500×) and high magnification (10000×). Finally, ImageJ and Fiji software were used for binarization to distinguish between pores and the substrate, and the porosity could be calculated.

[0078] Table 2 Parameters of the negative electrode active layer It should be noted that in Table 2: (1) The weight percentage of the first graphite and SiO2 refers to the weight percentage based on the total weight of the first negative electrode active material; (2) The median particle size of the first graphite 1 Dv50, median particle size of second graphite 2 Median particle size of Dv50 and SiO2 3 Dv50 was obtained by particle size analyzer; (3) The porosity P1% of the first negative electrode active layer, the porosity P2% of the second negative electrode active layer, and the porosity P% of the negative electrode active layer (including the first negative electrode active layer and the second negative electrode active layer) were obtained by cross-sectional imaging combined with image analysis. Specifically, the negative electrode sheet was first brittlely broken with liquid nitrogen to obtain a flat cross-section. Then, the cross-section was sprayed with gold to enhance conductivity. The structure of the negative electrode active layer was observed by SEM at low magnification (500×) and high magnification (10000×). Finally, ImageJ and Fiji software were used for binarization to distinguish the pores from the substrate, and the porosity could be calculated.

[0079] Application performance testing 1. Dissipative resistance (DCR) of a secondary battery: At 25±2℃, the secondary battery obtained in the above embodiment or comparative example was charged to 3.65V at 0.5C, then discharged at 1C current density for 30min, adjusted to 50% SOC, and then discharged at 2C constant current pulse for 10s and charged for 10s. The DCR0 was calculated as (voltage before pulse discharge – voltage after pulse discharge) / 2C × 100%. 2. Fast charging cycle performance of secondary batteries: At 25°C, the secondary batteries prepared in the above embodiments or comparative examples were charged at a rate of 2.2C and discharged at a rate of 2.2C, and charge-discharge cycled in the range of 10% SOC to 90% SOC until the capacity of the secondary battery was less than 80% of the initial capacity, and the number of cycles N was recorded. Then, at 25±2℃, the secondary battery, after N cycles (with the secondary battery capacity less than 80% of the initial capacity), was charged to 3.65V at 0.5C, then discharged at 1C current density for 30 minutes, adjusted to 50% SOC, and then discharged at 2C constant current pulse discharge for 10 seconds and charged for 10 seconds. The DCR was calculated. N = (Voltage before pulse discharge – Voltage after pulse discharge) / 2C × 100%; The calculated cyclic DCR growth rate = (DCR) N -DCR0) / DCR0×100%.

[0080] 3. Storage life test of secondary batteries: The secondary batteries prepared in the example were stored in a constant temperature chamber at 25°C. Every 30 days, they were taken out of the chamber for a re-capacity test until the battery capacity was less than 80% of the initial capacity. The number of storage days was recorded.

[0081] 4. Energy density test of secondary batteries: The secondary battery is weighed to obtain its mass m. The secondary battery is charged at a rate of 0.33C to 4.25V and discharged at a rate of 0.33C to 2.5V to obtain its discharge capacity. The mass energy density is calculated as discharge capacity × (4.25 - 2.5) / m.

[0082] 5. Testing of the peel force (F) between the negative electrode active layer and the negative electrode current collector in the negative electrode sheet: The negative electrode sheet was removed from the secondary battery. A sample measuring 40 × 10 cm (length × width) was cut from the negative electrode sheet. The sample was then fixed in a testing fixture. The tensile testing machine was started, and the upper fixture was moved at a constant speed of 400 mm / min to apply a peeling force to the sample. The force-displacement curve during the peeling process was recorded using the instrument's software or data acquisition system. The formula for calculating the peeling force is: Peel force (N / m) = Maximum peel force (N) / Sample width (m).

[0083] Table 3 Performance Test Results The above results indicate that: The positive electrode active layer of this application satisfies: 0.10 ≤ [Ni3+ ] / [Ni 4+ The concentration of lithium ions is ≤0.95, which allows some lithium ions to participate in the formation of the SEI film on the negative electrode during the battery cycle; the other part is pre-existing in the negative electrode as active lithium. The active lithium pre-existing in the negative electrode can be slowly released during subsequent cycles to improve the cycle performance of the secondary battery at a 2C current density, storage life, and at the same time improve the energy density.

[0084] This application further discovers that when a secondary battery satisfies the empirical formula: 40≤Z=0.8×A×T+2×(1-P)×F≤80, the cycle life, fast charging performance, and energy density of the secondary battery can be further improved. For example, the Z values ​​of Examples 12 and 14 fall outside the range of 40~80, and compared with other examples, the DCR cycle growth rate is higher.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, characterized in that, The secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector; the positive active layer includes a positive active material composition; The positive electrode active material composition includes lithium transition metal phosphate and lithium nickel cobalt manganese oxide; The positive electrode active layer satisfies: 0.10 ≤ [Ni 3+ ] / [Ni 4+ ]≤0.95, where, [Ni 3+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 3+ The peak area of ​​[Ni] 4+ The image shows the Ni content of the positive electrode active layer in the XPS spectrum. 4+ The peak area.

2. The secondary battery according to claim 1, characterized in that, The positive electrode active material layer also includes a lithium replenishing agent, which includes lithium-rich nickel oxide.

3. The secondary battery according to claim 2, characterized in that, In the positive electrode active layer, the mass ratio of the lithium-rich nickel oxide and the positive electrode active material composition is A, which satisfies: 0.01≤A≤0.

12.

4. The secondary battery according to claim 2, characterized in that, The mass ratio of the lithium-rich nickel oxide to the lithium nickel cobalt manganese oxide is 1:(1~5).

5. The secondary battery according to claim 1, characterized in that, It satisfies at least one of the following characteristics: (1) The general structural formula of the lithium-rich nickel oxide is Li X NiO2, 1≤x≤2; (2) The general structural formula of the lithium nickel cobalt manganese oxide is Li a Ni b Co c Mn d M e O2, where 0.9≤a≤1.1, 0<b<1, 0<c<1, 0<d<1, 0≤e≤0.3, b+c+d+e=1, and M is selected from at least one element from Y, Ti, Na, Fe, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, and V; (3) The lithium transition metal phosphate includes at least one of lithium iron phosphate and lithium manganese iron phosphate.

6. The secondary battery according to claim 1, characterized in that, The positive electrode active material composition satisfies: 2.0≤T=(Dv90-Dv10) / Dv50≤3.1 Wherein, Dv10 is the particle size corresponding to a cumulative volume percentage of 10% for the positive electrode active material composition, in μm; Dv50 is the particle size corresponding to a cumulative volume percentage of 50% in the positive electrode active material composition, in μm. Dv90 is the particle size corresponding to a cumulative volume percentage of 90% for the positive electrode active material composition, expressed in μm.

7. The secondary battery according to claim 6, characterized in that, The positive electrode active material composition satisfies at least one of the following characteristics: (1) 0.3μm≤Dv10≤1μm; (2) 1μm≤Dv50≤3μm; (3) 2μm≤Dv90≤7μm.

8. The secondary battery according to claim 1, characterized in that, The secondary battery further includes a negative electrode sheet, which includes a negative current collector and a first negative active layer and a second negative active layer disposed on at least one side surface of the negative current collector, wherein the first negative active layer is disposed between the negative current collector and the second negative active layer. The porosity of the first negative electrode active layer is P1, and the porosity of the second negative electrode active layer is P2, where P1 < P2.

9. The secondary battery according to claim 8, characterized in that, It satisfies at least one of the following characteristics: （1）25%≤P1%≤35%； （2）30%≤P2%≤45%。 10. The secondary battery according to claim 8, characterized in that, The first negative electrode active layer includes a first negative electrode active material, which comprises first graphite and silicon-based material, wherein the median particle size of the first graphite is [missing information]. 1 Dv50; The second negative electrode active layer contains a second negative electrode active material, which includes a second graphite, the median particle size of which is... 2 Dv50; satisfies: 1 Dv50> 2 Dv50; in, 1 Dv50 represents the particle size corresponding to when the cumulative volume percentage of the first graphite reaches 50%, in μm; 2 Dv50 represents the particle size corresponding to when the cumulative volume percentage of the second graphite reaches 50%, in μm.

11. The secondary battery according to claim 10, characterized in that, It satisfies at least one of the following characteristics: (1)13μm≤ 1 Dv50≤17μm; (2)10μm≤ 2 Dv50≤14μm。 12. The secondary battery according to claim 10, characterized in that, Based on the total mass of the first negative electrode active material, the mass percentage of the silicon-based material is 1% to 10%.

13. The secondary battery according to claim 8, characterized in that, The silicon-based material includes silicon oxide compounds, and the median particle size of the silicon oxide compounds is... 3 Dv50 is 1~3μm. 3 Dv50 represents the particle size corresponding to a cumulative volume percentage of 50% for the silicon oxide compound.

14. An electrical appliance, characterized in that, The electrical equipment includes a secondary battery as described in any one of claims 1 to 13.

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