Positive electrode sheet, secondary battery, and electric device

Abstract

A positive electrode sheet, a secondary battery, and an electric device. The positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer located on at least one side of the positive electrode current collector, and a base coating located between the positive electrode current collector and the positive electrode active material layer; the base coating comprises an additive, and the additive comprises a compound containing at least one group among a carboxylic acid group, a phosphate group, and a fluoro group. The provision of the base coating between the positive electrode current collector and the positive electrode active material layer can effectively reduce corrosion of an electrolyte to the positive electrode current collector. Moreover, the additive comprised in the base coating contains at least one group among the carboxylic acid group, the phosphate group, and the fluoro group and thus the additive can effectively complex and / or capture free aluminum ions, so that the effect of protecting the positive electrode current collector can be further achieved, and free aluminum ions can be prevented from migrating to a negative electrode, thereby avoiding damage to an SEI membrane by the free aluminum ions.

Description

Positive electrode sheet, secondary battery and electrical device

[0001] This application claims priority to Chinese patent application number 202311330871.5, filed on October 16, 2023, entitled “Positive Electrode Sheet, Secondary Battery and Electrical Device,” the entire text of which is hereby incorporated by reference. Technical Field

[0002] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0003] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0004] In recent years, the application of lithium-ion batteries has become increasingly widespread. They are widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. The development of lithium-ion battery technology has led to higher requirements for specific energy. High-energy-density battery designs typically utilize a high-nickel-silicon system and employ processes such as high-pressure densification and thick coating to achieve high specific energy. Because high-nickel materials have poor high-temperature stability and readily release oxygen at high temperatures, their lifespan decays rapidly and their safety is compromised. Adding lithium bis(fluorosulfonyl)imide to the electrolyte can effectively improve storage life and enhance safety. However, high-pressure densification damages the oxide film on the aluminum foil, exposing the fresh aluminum layer. The lithium bis(fluorosulfonyl)imide in the electrolyte corrodes the aluminum foil, causing it to fracture brittlely and raising safety concerns for lithium-ion batteries.

[0005] Summary of the Invention

[0006] The present application provides a positive electrode plate, a secondary battery and an electrical device to improve the high-temperature stability and storage life of the secondary battery, especially significantly improve the high-temperature stability and storage life of the secondary battery using a high-nickel and silicon system.

[0007] In order to achieve the above-mentioned object, the first aspect of the present application provides a positive electrode plate, comprising:

[0008] positive electrode current collector;

[0009] a positive electrode active material layer, located on at least one side of the positive electrode current collector; and

[0010] The undercoat layer is located between the positive electrode current collector and the positive electrode active material layer, and the undercoat layer contains an additive. The additive includes a compound containing at least one of a carboxylic acid group, a phosphoric acid group, and a fluorine group.

[0011] Therefore, by providing a primer layer between the positive electrode current collector and the positive electrode active material layer, the corrosion of the electrolyte on the positive electrode current collector can be effectively reduced; and since the additive contained in the primer layer includes at least one of a carboxylic acid group, a phosphoric acid group and a fluorine group, the additive can effectively complex and / or capture free aluminum ions. On the one hand, the free aluminum ions can be fixed between the positive electrode current collector and the primer layer, further playing a role in protecting the positive electrode current collector; on the other hand, the free aluminum ions can be prevented from migrating to the negative electrode, avoiding the free aluminum ions from damaging the SEI film; thereby improving the high temperature stability and storage life of the secondary battery and reducing the degree of damage to the battery at high temperatures.

[0012] In some embodiments, the additive has at least one of the following characteristics:

[0013] (1) the compound containing at least one of the carboxylic acid group and the phosphoric acid group includes one or more of ethylenediaminetetraacetic acid, cyclohexanecarboxylic acid, 3,5-dinitrosalicylic acid, glutamic acid, histidine, polybutylene phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2-phosphonobutane-1,2,4-tricarboxylic acid, 5-sulfosalicylic acid and 3-hydroxyphenylphosphatopropionic acid;

[0014] (2) The compound containing the fluorine group includes at least one of lithium hexafluorophosphate, fluorocarbonate, fluorophosphate, fluorocyclotriphosphazene and fluoroether.

[0015] In some embodiments, the fluorocarbonate includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoromethyl ethyl carbonate, and 2,2,2-trifluorodiethyl carbonate.

[0016] In some embodiments, the fluorophosphate includes one or more of tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methylphosphate, and bis(2,2,2-trifluoroethyl)ethylphosphate.

[0017] In some embodiments, the fluorinated cyclotriphosphazene includes one or more of methoxypentafluorocyclotriphosphazene, trifluoromethoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and 2,2,2-trifluoroethoxypentafluorocyclotriphosphazene.

[0018] In some embodiments, the fluoroether includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1,1,1,3,3,3-hexafluoroisopropyl methyl ether.

[0019] In some embodiments, the additive accounts for 5% to 25% by weight of the primer layer.

[0020] In some embodiments, the thickness of the primer layer is ≤ 4 μm.

[0021] In some embodiments, the first end of the positive electrode current collector is a tab production part for producing a tab. Along the length direction, the first end face of the positive electrode active material layer and the first end face of the primer layer are respectively adjacent to the end faces of the tab production part. The distance between the first end face of the primer layer and the end face of the tab production part is recorded as m1, and the distance between the first end face of the positive electrode active material layer and the end face of the tab production part is recorded as m2, 0mm≤m2-m1≤5mm.

[0022] In some embodiments, the second end face of the positive electrode active material layer and the second end face of the undercoat layer are respectively away from the end face of the tab making portion, the distance between the second end face of the undercoat layer and the end face of the tab making portion is recorded as m3, the distance between the second end face of the positive electrode active material layer and the end face of the tab making portion is recorded as m4, and the length of the positive electrode active material layer is recorded as L, 0≤m4-m3<L.

[0023] In some embodiments, 1 / 3L≤m4-m3<L.

[0024] In some embodiments, the primer layer further comprises a conductive agent and a binder; the conductive agent comprises one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene, and carbon fibers; and the binder comprises one or more of polyglutamic acid, styrene-butadiene rubber, olefin resins, and acrylic resins.

[0025] In some embodiments, the conductive agent accounts for 40%-70% by weight of the primer layer, and the binder accounts for 20%-50% by weight of the primer layer.

[0026] In some embodiments, the positive electrode active material layer comprises a positive electrode active material; the positive electrode active material comprises at least one of the following features:

[0027] (1) The positive electrode active material includes a lithium transition metal oxide having the following chemical formula: Li a Ni b Co c Mn d O2, 0.2<a≤1.2, 0.8≤b≤1, 0≤c≤0.1, 0≤d≤0.1, and b+c+d=1;

[0028] (2) the volume average particle size Dv50 of the positive electrode active material is ≥3 μm;

[0029] (3) The positive electrode active material includes one or more of single crystal particles and polycrystalline particles.

[0030] In some embodiments, the volume average particle size Dv50 of the positive electrode active material is 5 μm-9 μm.

[0031] In some embodiments, the compaction density of the positive electrode sheet is 3.5 g / cm 3 -3.8g / cm 3 .

[0032] The second aspect of the present application provides a secondary battery comprising the positive electrode sheet of the first aspect of the present application. The high temperature stability and storage life of the secondary battery comprising the positive electrode sheet can be significantly improved.

[0033] In some embodiments, the secondary battery further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode active material, wherein the negative electrode active material comprises one or more of a silicon-containing material and a carbon-based material;

[0034] Among them, the silicon-containing material includes one or more of silicon oxide and carbon-coated silicon oxide; the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon; the negative electrode active material includes silicon-containing material and carbon-based material, and the mass proportion of the silicon-containing material in the negative electrode active material is 3%-12%.

[0035] In some embodiments, the secondary battery further includes an electrolyte, the electrolyte comprising a first lithium salt and a second lithium salt; the first lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalatoborate); the second lithium salt comprises one or more of lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethylsulfonyl imide);

[0036] The electrolyte has at least one of the following characteristics:

[0037] (1) The mass of the first lithium salt accounts for 20% to 70% of the total mass of the first lithium salt and the second lithium salt;

[0038] (2) The total molar concentration of the first lithium salt and the second lithium salt is 0.5M-1.5M.

[0039] In some embodiments, the energy density of the secondary battery is ≥280Wh / Kg.

[0040] A third aspect of the present application provides an electrical device comprising the secondary battery of the second aspect of the present application.

[0041] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more of the accompanying drawings. The additional details or examples used to describe the accompanying drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes currently understood for these applications. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the accompanying drawings:

[0043] FIG1 is a schematic cross-sectional view of a positive electrode sheet along the length direction according to one embodiment of the present application.

[0044] FIG2 is a schematic cross-sectional view of a positive electrode sheet along the length direction according to an embodiment of the present application.

[0045] FIG3 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0046] FIG. 4 is an exploded view of the battery cell shown in FIG. 3 according to an embodiment of the present application.

[0047] FIG5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0048] FIG6 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0049] FIG. 7 is an exploded view of the battery pack shown in FIG. 6 according to an embodiment of the present application.

[0050] FIG8 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0051] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 housing; 52 electrode assembly; 53 cover plate; 6 electrical device. DETAILED DESCRIPTION

[0052] Below, some embodiments of the battery cells, secondary batteries, and electrical devices of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0053] " scope " disclosed in the present application can be limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are also listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is merely an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to listing the parameter as, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on. For example, when a parameter is expressed as an integer selected from "2-10", this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0054] In this application, "a plurality of" or "a plurality of" refers to a number greater than or equal to 2 unless otherwise specified. For example, "one or more" means one or more than or equal to two.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0056] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of such phrases in various locations in the specification does not necessarily refer to the same embodiment, nor does it necessarily refer to independent or alternative embodiments that are mutually exclusive with other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments. References to "implementations" herein have a similar understanding.

[0057] It will be appreciated by those skilled in the art that, in the methods of various embodiments or examples, the order in which the steps are written does not imply a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible inherent logic. Unless otherwise specified, all steps of the present 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 steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0058] In this application, in the open technical features or technical solutions described with words such as "contain", "include", and "include", unless otherwise specified, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions that also include additional members in addition to the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2, and a3" and the feature or solution of "A includes not only a1, a2, and a3, but also other members". In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0059] In this application, the terms "optionally," "optional," and "optional" are optional and refer to either option being present or absent. If a technical solution contains multiple "options," each option is considered independent unless otherwise specified and there are no conflicts or constraints.

[0060] In related technologies, high-energy-density battery designs usually use a high-nickel and silicon system design, and adopt processes such as high-pressure density and thick coating to achieve high-energy-density. In addition, lithium bis(fluorosulfonyl)imide is added to the electrolyte. When high-pressure density destroys the oxide film on the surface of the aluminum foil, lithium bis(fluorosulfonyl)imide may corrode the fresh aluminum foil, causing safety problems for lithium-ion batteries.

[0061] In addition, due to the large expansion of the silicon system, the pulling effect on the tabs and corners is large, so the electrolyte may cause more serious corrosion to the aluminum foil at the tabs and corners.

[0062] As the compaction density increases, the energy density increases, but the electrolyte corrodes the aluminum foil, the tensile strength of the positive electrode sheet decreases, the shallow puncture boundary worsens, the battery internal resistance increases, and the battery storage life deteriorates. As the silicon content of the negative electrode increases, the energy density increases, but the expansion of the negative electrode sheet increases, which also leads to worsening electrolyte corrosion of the aluminum foil, reduced tensile strength of the positive electrode sheet, worsening shallow puncture boundary, and worsening battery storage life. As the amount of lithium bis(fluorosulfonyl)imide in the electrolyte increases, the electrolyte corrosion of the aluminum foil will further worsen.

[0063] In response to the above problems, the present application provides a positive electrode plate. By setting a primer layer between the positive electrode collector and the positive electrode active material layer of the positive electrode plate, the probability of the positive electrode collector being corroded by the electrolyte can be effectively reduced; and the additives in the primer layer contain groups that can effectively complex and / or capture aluminum ions, which can reduce damage to the negative electrode SEI film.

[0064] The first aspect of the present application provides a positive electrode plate, comprising a positive electrode current collector, a positive electrode active material layer located on at least one side of the positive electrode current collector, and a primer layer located between the positive electrode current collector and the positive electrode active material layer; the primer layer contains an additive, and the additive includes a compound containing at least one of a carboxylic acid group, a phosphoric acid group, and a fluorine group.

[0065] It can be understood that by providing a primer layer between the positive electrode current collector and the positive electrode active material layer, the corrosion of the electrolyte on the positive electrode current collector can be effectively reduced; and since the additive contained in the primer layer contains at least one of a carboxylic acid group, a phosphoric acid group and a fluorine group, the additive can effectively complex and / or capture free aluminum ions. On the one hand, the free aluminum ions can be fixed between the positive electrode current collector and the primer layer, further playing a role in protecting the positive electrode current collector; on the other hand, it can also prevent the free aluminum ions from migrating to the negative electrode, avoiding the free aluminum ions from damaging the SEI film; thereby improving the high temperature stability and storage life of the secondary battery and reducing the degree of damage to the battery at high temperatures.

[0066] In addition, by providing a primer layer, the tensile strength of the electrode can be increased, the discharge DCR of the secondary battery can be reduced, and the storage life of the secondary battery can be increased.

[0067] As a possible embodiment, the compound containing at least one of a carboxylic acid group and a phosphoric acid group includes one or more of ethylenediaminetetraacetic acid, cyclohexanecarboxylic acid, 3,5-dinitrosalicylic acid, glutamic acid, histidine, polybutylene phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2-phosphonobutane-1,2,4-tricarboxylic acid, 5-sulfosalicylic acid and 3-hydroxyphenylphosphatopropionic acid.

[0068] As a possible implementation, the compound containing a fluorine group includes at least one of lithium hexafluorophosphate, fluorocarbonate, fluorophosphate, fluorocyclotriphosphazene and fluoroether.

[0069] In some optional embodiments, the fluorinated carbonate includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoroethyl methyl carbonate and 2,2,2-trifluorodiethyl carbonate.

[0070] In some optional embodiments, the fluorophosphate includes one or more of tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methylphosphate and bis(2,2,2-trifluoroethyl)ethylphosphate.

[0071] In some optional embodiments, the fluorinated cyclotriphosphazene includes one or more of methoxypentafluorocyclotriphosphazene, trifluoromethoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene and 2,2,2-trifluoroethoxypentafluorocyclotriphosphazene.

[0072] In some optional embodiments, the fluoroether includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,1,3,3,3-hexafluoroisopropyl methyl ether.

[0073] As an example, the types of groups and compounds contained in the additives in the above-mentioned primer layer can be determined by infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS); the specific method is as follows: take a small amount of positive electrode sheet, scrape off the powder, place it in a 100°C oven to dry for 12 hours, and set aside; use an infrared spectrometer to determine whether there is 3500-3300cm -1 The peak at 1600 cm -1 The C=O characteristic peak at 288.4 eV was determined by X-ray electron spectroscopy (XPS) to determine whether there was a carboxylic acid group; the infrared spectrometer was used to determine whether there was a C=O characteristic peak at 1350-1250 cm -1 The peak at 2700-2200 cm -1 The hydroxyl characteristic peak at 531.3 eV was determined by X-ray electron spectroscopy (XPS) to determine whether there was a P=O characteristic peak at 531.3 eV to determine whether there was a phosphate group; the infrared spectrometer was used to determine whether there was a 1350-1000 cm -1 The presence of a CF bond characteristic peak at 290 eV was determined by X-ray electron spectroscopy (XPS) to determine whether there was a CF bond characteristic peak at 290 eV to determine whether there was a fluorine group.

[0074] In some embodiments, the weight percentage of the additive in the primer layer is 5%-25%. For example, it can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or a range between any two of the foregoing values. When the weight percentage of the additive in the primer layer is within the above range, the corrosion and dissolution of Al can be effectively suppressed, the DCR is reduced, and the service life is improved.

[0075] It should be noted that the primer layer also contains a conductive agent and a binder, and the mass ratio of the additive, conductive agent, and binder in the primer layer can be determined simultaneously. As an example, the mass ratio of the additive, conductive agent, and binder in the primer layer can be determined by the following method: take the positive electrode sheet containing the primer layer, scrape off the powder, wash the powder with DME, dry it, and weigh the powder mass m0; add "aqua regia" to the powder, and digest it with microwave high temperature (~200℃) and high pressure (~120bar) for 6h, and separate the digestion product into liquid and residue; weigh the residue to obtain the mass m1 of the conductive agent; measure the P and N content in the liquid by inductively coupled plasma emission spectrometry (ICP), and deduce the mass m2 of the additive; the mass of the binder is m0-m1-m2; further calculate the mass ratio of the additive, conductive agent, and binder in the primer layer.

[0076] In some embodiments, the thickness of the primer layer is ≤ 4 μm; for example, the thickness can be, but is not limited to, 0.01 μm, 0.05 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, 1.8 μm, 2 μm, 2.3 μm, 2.5 μm, 2.7 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, or a range between any two of the foregoing values. When the thickness of the primer layer is set within the above range, it effectively prevents the electrolyte from corroding the current collector while also improving the energy density and cycle life of the secondary battery.

[0077] As an example, the thickness of the primer layer mentioned above can be measured by the following method: take a pole piece and measure the thickness of the primer layer of the pole piece by cross-sectional polishing-scanning electron microscopy (CP-SEM).

[0078] In some embodiments, the first end of the positive electrode current collector is a tab fabrication portion for fabricating a tab. Along the length direction, the first end surface of the positive electrode active material layer and the first end surface of the undercoat layer are respectively adjacent to the end surface of the tab fabrication portion. The distance between the first end surface of the undercoat layer and the end surface of the tab fabrication portion is recorded as m1, and the distance between the first end surface of the positive electrode active material layer and the end surface of the tab fabrication portion is recorded as m2, 0 mm ≤ m2 - m1 ≤ 5 mm.

[0079] Optionally, the second end face of the positive electrode active material layer and the second end face of the undercoat layer are respectively away from the end face of the tab making portion, the distance between the second end face of the undercoat layer and the end face of the tab making portion is recorded as m3, the distance between the second end face of the positive electrode active material layer and the end face of the tab making portion is recorded as m4, and the length of the positive electrode active material layer is recorded as L, 0≤m4-m3<L; it can be optionally 1 / 3L≤m4-m3<L.

[0080] It should be noted that the “first end”, “first end face” and “second end face” mentioned above are for descriptive purposes only and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features.

[0081] The m2-m1 mentioned above can be, but is not limited to, 0 mm, 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 1.3 mm, 1.5 mm, 1.7 mm, 2 mm, 2.3 mm, 2.5 mm, 2.7 mm, 3 mm, 3.3 mm, 3.5 mm, 3.7 mm, 4 mm, 4.3 mm, 4.5 mm, 4.7 mm, 5 mm, or a range between any two of the above values. The m2-m1 being within the above range indicates that the first end face of the undercoat layer is closer to the end face of the tab fabrication portion than the positive electrode active material layer, thereby improving the protective effect of the undercoat layer on the positive electrode current collector.

[0082] The m4-m3 mentioned above can be but not limited to 0, 5 / 100L, 10 / 100L, 15 / 100L, 20 / 100L, 25 / 100L, 30 / 100L, 1 / 3L, 35 / 100L, 40 / 100L, 45 / 100L, 50 / 100L, 55 / 100L, 60 / 100L, 65 / 100L, 70 / 100L, 75 / 100L, 80 / 100L, 85 / 100L, 90 / 100L, 95 / 100L, 96 / 100L, 97 / 100L, 98 / 100L, 99 / 100L or a range between any two of the above values. When m4-m3 is 0, it indicates that the second end face of the positive electrode active material layer is flush with the second end face of the undercoat layer; when 0<m4-m3<L, it indicates that compared with the positive electrode active material layer, the second end face of the undercoat layer is closer to the end face of the tab production part; usually, the aluminum foil near the tab or corner is more severely corroded by the electrolyte. Therefore, by arranging the undercoat layer at the end face close to the tab production part, the corrosion of the electrolyte on the positive electrode current collector can also be effectively reduced, thereby improving the safety of the secondary battery.

[0083] Figure 1 is a schematic cross-sectional view of a positive electrode sheet along its length, provided in one embodiment of the present application. As shown in Figure 1 , a primer layer 112 is disposed on one surface of a positive electrode current collector 113, and a positive electrode active material layer 111 is disposed on a surface of the primer layer 112 away from the positive electrode current collector 113. The primer layer 112 does not completely coat the positive electrode current collector 113; at least one side of the primer layer 112 is exposed to form a tab portion.

[0084] In the example shown in Figure 1, the first end face 111a of the positive electrode active material layer 111 and the first end face 112a of the primer layer 112 are close to the end face 113a of the tab production part of the positive electrode current collector 113, and the second end face 111b of the positive electrode active material layer 111 and the second end face 112b of the primer layer 112 are flush.

[0085] FIG2 is a schematic cross-sectional view of a positive electrode sheet along its length, provided in another embodiment of the present application. The example shown in FIG2 is substantially the same as FIG1 , with the primary difference being that the positive electrode active material layer 211 is not entirely located on the undercoat layer 212. Instead, a portion of the positive electrode active material layer 211 is located on the undercoat layer 212, and a portion is directly in contact with the positive electrode current collector 213. The positive electrode current collector 213 is exposed on one side of the undercoat layer 212 to form the tab formation portion.

[0086] In the example shown in Figure 2, the first end face 211a of the positive electrode active material layer 211 and the first end face 212a of the undercoat layer 212 are close to the end face 213a of the tab production part of the positive electrode current collector 213, and compared with the second end face 211b of the positive electrode active material layer 211, the second end face 212b of the undercoat layer 212 is closer to the end face 213a of the tab production part of the positive electrode current collector 213.

[0087] The "length direction" mentioned above refers to the direction from one side of the positive electrode current collector where the tab is formed to the other side. It should be noted that the "length" and "length direction" mentioned above are only used to describe the relative positional relationship between the positive electrode current collector, the positive electrode active material layer, and the undercoat layer, and are not intended to limit the positive electrode sheet. For descriptive purposes, the "width" and "width direction" may also be used to describe the corresponding terms, without specific limitation.

[0088] In some embodiments, the primer layer further comprises a conductive agent and a binder.

[0089] In some optional embodiments, the conductive agent includes one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0090] In some optional embodiments, the binder includes one or more of polyglutamic acid, styrene-butadiene rubber, olefin resin and acrylic resin.

[0091] In some optional embodiments, the weight percentage of the conductive agent in the primer layer is 40%-70%. For example, it can be, but is not limited to, 40%, 43%, 45%, 48%, 50%, 52%, 55%, 57%, 60%, 63%, 65%, 68%, 70%, or a range between any two of the foregoing values. When the weight percentage of the conductive agent in the primer layer is within the above range, the conductivity of the primer layer is improved while facilitating the function of the additive in the primer layer.

[0092] In some optional embodiments, the binder accounts for 20% to 50% by weight of the primer layer; for example, it can be, but is not limited to, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, 40%, 43%, 45%, 48%, 50%, or a range between any two of the foregoing values. When the binder accounts for a mass fraction of the primer layer within the foregoing range, it facilitates uniform dispersion of the conductive agent and additives in the primer layer, and can provide the primer layer with both strong adhesion and good conductivity.

[0093] In some embodiments, the positive active material layer includes a positive active material.

[0094] In some optional embodiments, the positive electrode active material includes a lithium transition metal oxide having the following chemical formula: Li a (A b Co c Mn d Al e )O2, wherein the element A includes at least one of Ni and Fe; 0.2<a≤1.2, 0≤b≤1, 0≤c≤0.2, 0≤d≤0.2, 0≤e≤0.2, and b+c+d+e=1;

[0095] Optionally, the positive electrode active material includes a lithium transition metal oxide having the following chemical formula: Li a Ni b Co c Mn d O2, 0.2<a≤1.2, 0.8≤b≤1, 0≤c≤0.1, 0≤d≤0.1, and b+c+d=1.

[0096] It should be noted that the above definition of a includes the molar content of Li in different charge and discharge states of the battery (usually the battery voltage is between 2-5V).

[0097] It is understandable that the battery will be accompanied by lithium (Li) deintercalation and consumption during the charge and discharge process, and the content of Li in the positive electrode plate is different when the battery is discharged to different states. In the list of positive electrode materials in this application, unless otherwise specified, the Li content is the initial state of the material. The positive electrode material is applied to the positive electrode plate in the battery system, and after the charge and discharge cycle, the Li content in the positive electrode material contained in the plate will usually change. Among them, the Li content can be measured by molar content, but is not limited to this. Regarding "the Li content is the initial state of the material", the initial state of the material refers to the state before the material is added to the positive electrode slurry. It is understandable that new materials obtained by appropriate modification on the basis of the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode materials, and non-limiting examples include coating modification.

[0098] In the examples of positive electrode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual O content will fluctuate. The O content can be measured by molar content, but is not limited to this.

[0099] In some embodiments, the positive electrode active material may also be a positive electrode active material for batteries known in the art. As non-limiting examples, the positive electrode active material may also include one or more of the following materials: olivine-structured lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of olivine-structured lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.80 Co 0.15 Al 0.05 O2.

[0100] In some optional embodiments, the volume average particle size Dv50 of the positive electrode active material is ≥3 μm, which can be 5 μm-9 μm; for example, it can be but is not limited to 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm or a range between any two of the above values.

[0101] As an example, the volume average particle size Dv50 of the positive electrode active material mentioned above can be conveniently measured with a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, with reference to GB / T 19077-2016 particle size distribution laser diffraction method.

[0102] In some optional embodiments, the positive electrode active material includes one or more of single crystal particles and polycrystalline particles. Using a positive electrode active material containing both single crystal particles and polycrystalline particles can improve both the cycle performance and specific capacity of the secondary battery. The combination of large and small particles can effectively increase the specific energy of the secondary battery.

[0103] In some embodiments, the positive electrode 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 material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0104] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0105] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0106] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the additives, conductive agent, and binder for preparing the primer layer, are dispersed in water to form a primer slurry; the primer slurry is applied to at least one side of the positive electrode current collector and dried to obtain the primer layer; the positive electrode active material, conductive agent, binder, and any other components for preparing the positive electrode active material layer are then dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is applied to the primer layer surface, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from, but not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the primer slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector. The solid content of the primer slurry can be 20wt%-30wt%. The viscosity of the primer slurry at room temperature can be adjusted to 1500-3000mPa·s. The solid content of the positive electrode slurry may be 40 wt%-80 wt% and the viscosity of the positive electrode slurry at room temperature may be adjusted to 5000-25000 mPa·s.

[0107] In some embodiments, the compacted density of the positive electrode sheet is ≥3.5 g / cm 3 , optional 3.5g / cm 3 -3.8g / cm 3 ; For example, it can be but not limited to 3.5g / cm 3 、3.55g / cm 3 、3.6g / cm 3 、3.65g / cm 3 、3.7g / cm 3 、3.75g / cm 3 、3.8g / cm 3 Or the range between any two of the above values.

[0108] As an example, the compaction density of the positive electrode sheet mentioned above can be measured by the following method: take a circular positive electrode sheet with a diameter of 14 mm, calculate the area S of the positive electrode sheet, measure its thickness d, weigh the weight m of the active material layer excluding the positive electrode current collector, and thus calculate the compaction density of the positive electrode sheet PD = m / Sd.

[0109] The second aspect of the present application provides a secondary battery comprising the positive electrode sheet of the first aspect. The high-temperature stability and storage life of the secondary battery comprising the positive electrode sheet can be significantly improved.

[0110] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0111] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte in the electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0112] In some embodiments, the secondary battery further comprises a negative electrode plate containing a negative electrode active material, which includes one or more of a silicon-containing material and a carbon-based material. The negative electrode active material includes a silicon-containing material, i.e., the introduction of a silicon system into the negative electrode plate can increase the negative electrode plate's energy density. Combined with the use of a high-nickel material as the positive electrode active material, the secondary battery's energy density can reach 280Wh / Kg or higher.

[0113] In some optional embodiments, the silicon-containing material includes one or more of silicon oxide and carbon-coated silicon oxide.

[0114] In some optional embodiments, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0115] In some optional embodiments, the negative electrode active material includes a silicon-containing material and a carbon-based material, and the weight percentage of the silicon-containing material in the negative electrode active material is 3%-12%. For example, it can be, but is not limited to, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, or a range between any two of the above values. When the weight percentage of the silicon-containing material in the negative electrode active material is within the above range, it can meet high capacity requirements while avoiding electrode rupture caused by expansion of the silicon-containing material.

[0116] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0117] As a non-limiting example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on either or both of the two facing surfaces of the negative electrode current collector.

[0118] In some of these embodiments, the negative electrode active material may also be a negative electrode active material for a battery that is well known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may include one or more of elemental silicon, silicon-nitrogen complexes, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional 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.

[0119] 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 material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0120] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more 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).

[0121] In some embodiments, the negative electrode active material layer may optionally include other conductive agents known in the art for negative electrode sheets. The conductive agent may include one or more of superconducting carbon, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the negative electrode active material layer may optionally further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the graded porous carbon tube, the second conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or two surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000-10000mPa·s. The compaction density of the negative electrode sheet can be 1.0g / cm 3 -1.8g / cm 3 .

[0124] In some embodiments, the secondary battery further includes an electrolyte comprising a first lithium salt and a second lithium salt. The first lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(oxalatoborate), and the second lithium salt comprises one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide. Including both the first and second lithium salts in the electrolyte can improve the stability of the electrolyte system and reduce corrosion to the substrate.

[0125] In some optional embodiments, the mass percentage of the first lithium salt to the total mass of the first lithium salt and the second lithium salt is 20%-70%; for example, it can be, but is not limited to, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range between any two of the foregoing values. When the mass percentage of the first lithium salt to the total mass of the first lithium salt and the second lithium salt is within the above range, the stability of the electrolyte system can be improved while also reducing corrosion to the substrate.

[0126] In some optional embodiments, the total molar concentration of the first lithium salt and the second lithium salt is 0.5M-1.5M; for example, it can be but is not limited to 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M or a range between any two of the above values.

[0127] As an example, the percentage of the mass of the first lithium salt to the total mass of the first lithium salt and the second lithium salt, and the total molar concentration of the first lithium salt and the second lithium salt mentioned above can be determined by the following method: taking an electrolyte sample, volatilizing to remove the solvent, and measuring the content of the first lithium salt characteristic elements (P, B, F) and the second lithium salt characteristic elements (N, S) in the electrolyte by inductively coupled plasma emission spectrometry (ICP), and then calculating the percentage of the mass of the first lithium salt to the total mass of the first lithium salt and the second lithium salt, as well as the total molar concentration of the first lithium salt and the second lithium salt.

[0128] In some embodiments, the energy density of the secondary battery is ≥ 280 Wh / Kg.

[0129] In some embodiments, the electrolyte salt in the electrolyte may further include one or more of lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium difluorodioxalatophosphate (LiDFOP), and lithium tetrafluorooxalatophosphate (LiTFOP). The electrolyte has the function of conducting ions between the positive electrode and the negative electrode.

[0130] In some embodiments, the solvent in the electrolyte may include ethylene carbonate (EC, ), propylene carbonate (PC, ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate One or more of fluoroethylene carbonate (FEC), 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.

[0131] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0132] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0133] Isolation film

[0134] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0135] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0136] In some embodiments, the isolation film has a thickness of 6 μm-40 μm, and optionally 12 μm-20 μm.

[0137] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0138] In some embodiments, the battery cell may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0139] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the battery cell may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic. Non-limiting examples of the plastic include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0140] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0141] In this application, unless otherwise specified, a "battery cell" refers to a basic unit that can achieve the mutual conversion of chemical energy and electrical energy. Further, generally speaking, it includes at least a positive electrode plate, a negative electrode plate, and an electrolyte. During the battery's charge and discharge process, active ions are embedded in and out of the positive and negative electrode plates. The electrolyte plays the role of conducting active ions between the positive and negative electrode plates.

[0142] The present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. For example, FIG3 shows a battery cell 5 with a square structure as an example.

[0143] In some embodiments, referring to FIG4 , the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to actual needs.

[0144] The secondary battery may be a battery module or a battery pack.

[0145] A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0146] FIG5 shows an example battery module 4. Referring to FIG5 , in the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0147] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0148] In some embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select an appropriate number based on the application and capacity of the battery pack.

[0149] Figures 6 and 7 illustrate an example battery pack 1. Referring to Figures 6 and 7 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be positioned over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0150] In addition, the present application also provides an electrical device, which includes at least one of the battery cell and secondary battery provided in the present application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices can be, for example, mobile phones, laptops, etc.; electric vehicles can be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0151] As an electrical device, a battery cell or a secondary battery can be selected according to its usage requirements.

[0152] FIG8 shows an example of an electric device 6. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0153] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0154] Example

[0155] Below, the embodiment of the present application is described. The embodiment described below is exemplary, is only used to explain the present application, and is not to be construed as limiting the present application. Where the technology or conditions are not specified in the embodiment, the technology or conditions described in the literature in this area or the product instructions are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0156] Preparation of 1. Secondary Battery

[0157] Example 1

[0158] 1. Preparation of positive electrode sheet

[0159] Fluoroethylene carbonate (as an additive), acetylene black (as a conductive agent), and polyacrylic acid (as a binder) were mixed at mass percentages of 25 wt%, 55 wt%, and 20 wt%, respectively, and water was added to prepare a primer slurry with a solid content of 25%. The primer slurry was evenly coated on both sides of an aluminum foil, and dried to obtain an aluminum foil with a primer layer.

[0160] LiNi 0.95 Co 0.03 Mn 0.02O2 (as the positive electrode active material), acetylene black (as the conductive agent), and polyvinylidene fluoride (PVDF, as the binder) were dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 96.5:1.5:2 and thoroughly stirred to form a positive electrode slurry. This slurry was then evenly coated onto aluminum foil with a primer layer. The cathode sheet was then dried, cold-pressed, and slit. The thickness of the primer layer in the positive electrode sheet was measured to be 1 μm, and the compacted density of the positive electrode sheet was 3.5 g / cc.

[0161] 2. Preparation of negative electrode sheet

[0162] The active material graphite, silicon oxide, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 90:5:2:2:1, and are evenly mixed to prepare a negative electrode slurry. The slurry is coated on both sides of the copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0163] 3. Diaphragm

[0164] It uses PE diaphragm with PVDF and alumina coating on the surface to improve adhesion and heat resistance.

[0165] 4. Electrolyte

[0166] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then LiPF6:LiFSI (2:8) are uniformly dissolved in the above solution to obtain an electrolyte; the concentration of lithium salt in the electrolyte is 1 mol / L.

[0167] The positive electrode sheet, separator, and negative electrode sheet are stacked in order. The separator acts as an insulator between the positive and negative electrode sheets. The cells are then wound to form bare cells. The lugs are welded to the bare cells and placed in aluminum shells. The cells are then baked at 80°C to remove moisture. Electrolyte is randomly injected and sealed to produce an uncharged battery. The uncharged batteries undergo a series of processes, including resting, hot and cold pressing, formation, shaping, and capacity sequencing, to produce lithium-ion batteries.

[0168] Example 2-19

[0169] The preparation methods of the secondary batteries in Examples 2-19 are substantially the same as those in Example 1, with the main differences being at least one of the thickness of the primer layer, the mass ratio of the additive in the primer layer, and the type of additive. See Table 1 for details.

[0170] It should be noted that, in the bottom coating layer of the positive electrode sheet of Example 7, the mass proportion of the conductive agent is 50%, and the mass proportion of the binder is 20%.

[0171] In the bottom coating layer of the positive electrode sheet of Example 8, the mass proportion of the conductive agent is 60%, and the mass proportion of the binder is 20%.

[0172] In the bottom coating layer of the positive electrode sheet of Example 9, the mass proportion of the conductive agent is 40%, and the mass proportion of the binder is 50%.

[0173] In the bottom coating layer of the positive electrode sheet of Example 10, the mass proportion of the conductive agent is 70%, and the mass proportion of the binder is 25%.

[0174] In the bottom coating layer of the positive electrode sheet of Example 11, the mass proportion of the conductive agent is 50%, and the mass proportion of the binder is 47%.

[0175] In the bottom coating layer of the positive electrode plate of Example 12, the mass proportion of the conductive agent is 40%, and the mass proportion of the binder is 50%.

[0176] Comparative Example 1

[0177] The main differences between the secondary battery preparation method in Comparative Example 1 and the secondary battery preparation method in Example 1 are that only a conductive agent and a binder are added to the primer slurry, without any additives; the mass ratio of the conductive agent to the binder is 7:3; all other conditions are the same. See Table 1 for details.

[0178] Comparative Example 2

[0179] The difference between the preparation method of the secondary battery in Comparative Example 2 and the preparation method of the secondary battery in Comparative Example 1 is that no primer layer is prepared on the positive electrode sheet, and all other aspects are the same. Detailed information is shown in Table 1.

[0180] Comparative Example 3

[0181] The difference between the preparation method of the secondary battery in Comparative Example 3 and the preparation method of the secondary battery in Comparative Example 2 is that the ratio of LiPF6:LiFSI in the electrolyte is 7:3, and all other aspects are the same. See Table 1 for details.

[0182] Comparative Example 4

[0183] The difference between the preparation method of the secondary battery in Comparative Example 4 and the preparation method of the secondary battery in Comparative Example 2 is that the mass proportion of silicon oxide in the active material layer of the negative electrode is 20%, and all other aspects are the same. See Table 1 for details.

[0184] Comparative Example 5

[0185] The difference between the preparation method of the secondary battery in Comparative Example 5 and the preparation method of the secondary battery in Comparative Example 2 is that silicon oxide is not added to the active material layer of the negative electrode, and graphite of the same mass is used instead of silicon oxide. See Table 1 for details.

[0186] Comparative Example 6

[0187] The difference between the preparation method of the secondary battery in Comparative Example 6 and the preparation method of the secondary battery in Comparative Example 5 is that the compaction density of the positive electrode sheet is 3.6 g / cc, and all other aspects are the same. See Table 1 for details.

[0188] Comparative Example 7

[0189] The difference between the preparation method of the secondary battery in Comparative Example 7 and the preparation method of the secondary battery in Comparative Example 5 is that the compaction density of the positive electrode sheet is 3.7 g / cc, and all other aspects are the same. See Table 1 for details.

[0190] Comparative Example 8

[0191] The main difference between the preparation method of the secondary battery in Comparative Example 8 and the preparation method of the secondary battery in Example 1 is the type of additives; all other details are the same. See Table 1 for details.

[0192] The structural parameters of the secondary batteries in the above embodiments and comparative examples are shown in Table 1.

[0193] Table 1

[0194] Among them, w1 represents the mass proportion of the additive in the undercoat layer, w2 represents the mass proportion of the silicon-containing material in the negative electrode active material, w3 represents the mass proportion of LiFSI in the total lithium salt in the electrolyte, d represents the thickness of the undercoat layer, cd represents the compaction density of the positive electrode sheet, and FEC represents fluoroethylene carbonate.

[0195] It should be noted that the thickness of the undercoat layer in the above-mentioned positive electrode sheet is measured by the following method: take the positive electrode sheet and measure the thickness of the undercoat layer of the positive electrode sheet by cross-sectional polishing-scanning electron microscopy (CP-SEM).

[0196] The compaction density of the positive electrode sheet mentioned above is determined by the following method: take a circular positive electrode sheet with a diameter of 14 mm, calculate the area S of the positive electrode sheet, measure its thickness d, weigh the weight m of the active material layer excluding the positive electrode current collector, and thus calculate the compaction density of the positive electrode sheet PD = m / Sd.

[0197] 2. Secondary Battery Performance Test

[0198] 1. Shallow puncture test

[0199] The secondary batteries in the above embodiments and comparative examples were discharged at a rate of 1 / 3C to 2.8V at 25°C, allowed to stand for 60 minutes, and then charged at a rate of 1 / 3C to 4.25V, and then charged to a constant voltage of 0.05C. After standing for 60 minutes, part of the battery shell was removed, and the voltage, internal resistance, and weight of the battery cell were recorded.

[0200] The nail penetration test was carried out at 25°C. The nail had a diameter of 1 mm and was inserted at a speed of 0.1 mm / s at a uniform speed perpendicular to the direction of the battery plate. The penetration position was close to the geometric center of the punctured surface. The penetration depth was 4 mm, and the voltage drop was monitored. The battery was observed under the test environment for 1 hour. If there was no failure, the penetration depth was increased to 5 mm, and the above steps were repeated until failure occurred. The voltage, internal resistance, and weight of the battery cell at the time of failure were recorded. The results are shown in Table 2.

[0201] 2. Storage days test

[0202] The secondary batteries in the above examples and comparative examples were stored at 60°C and 97% SOC. Before and during storage, the initial reversible capacity (C0) and actual reversible capacity (Cn) of the battery cells were measured, respectively. The batteries were removed and tested every 15 days. The testing process was as follows: Each secondary battery was allowed to rest at 25°C for 30 minutes, then charged at a rate of 1 / 3C to 4.25V, then charged to 0.05C at constant voltage. The battery was allowed to rest for 30 minutes, then discharged at a rate of 1 / 3C to 2.8V, and the initial reversible capacity (C0) was recorded. Testing was performed every 15 days, and Cn (n = 1, 2, 3, 4, 5, ...) was recorded. When Cn / C0 ≤ 80%, n was recorded. The number of days of end-of-life storage (EOL) = 15*n. The results are shown in Table 2.

[0203] 3. Tensile strength test

[0204] During the tensile process, the positive electrode plate undergoes a tensile strength test. After the material passes through the yielding stage and enters the strengthening stage, as the cross-sectional dimensions significantly decrease, the maximum force (Fb) it withstands at break is divided by the original cross-sectional area (So) of the specimen. This stress (σ) is called the tensile strength or ultimate strength, and is measured in N / m² (or MPa). It represents the maximum ability of a metal material to resist damage under tension. The results are shown in Table 2.

[0205] The calculation formula for tensile strength is: σ=Fb / So

[0206] Where: Fb is the maximum force that the specimen can withstand when it is broken, N (Newton); So is the original cross-sectional area of ​​the specimen, mm2.

[0207] The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0208] Table 2

[0209] From the comparison of the results of Example 1-19 and Comparative Example 1-8, it can be seen that the positive electrode plate provided by the present application has a higher tensile strength, and can also improve the storage life of the secondary battery and increase the shallow puncture depth of the secondary battery.

[0210] The main difference between Examples 1-6 lies in the thickness of the primer layer; Example 6 has the thickest primer layer. Comparing the results of Examples 1-6, we can see that when the primer layer thickness is ≤4μm, the positive electrode sheet has higher tensile strength and deeper shallow penetration depth, and the secondary battery has a longer cycle life. This shows that when the primer layer thickness is ≤4μm, it can effectively prevent electrolyte corrosion of the current collector while also improving the tensile strength and cycle life of the positive electrode sheet and increasing the shallow penetration depth of the secondary battery.

[0211] The main difference between Example 2 and Examples 7-11 is that the mass proportion of the additives in the primer layer is different; the mass proportion of the additives in Example 7 is the largest, and the mass proportion of the additives in Example 11 is the smallest; compared with the results of Example 7 and Examples 7-11, it can be seen that when the mass proportion of the additives in the primer layer is 5%-25%, while protecting the current collector from corrosion by the electrolyte, it can also take into account the improvement of the tensile strength and shallow puncture depth of the positive electrode sheet and the storage life of the secondary battery.

[0212] The above description of the various embodiments tends to emphasize the differences between the various embodiments. The same or similar aspects can be referenced with each other and will not be repeated herein for the sake of brevity.

[0213] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode sheet, comprising: Positive electrode current collector; A positive electrode active material layer, located on at least one side of the positive electrode current collector; as well as The undercoat layer is located between the positive electrode current collector and the positive electrode active material layer, and the undercoat layer contains an additive, wherein the additive includes a compound containing at least one of a carboxylic acid group, a phosphoric acid group and a fluorine group.

2. The positive electrode sheet according to claim 1, wherein: The additive has at least one of the following characteristics: (1) the compound containing at least one of the carboxylic acid group and the phosphoric acid group includes one or more of ethylenediaminetetraacetic acid, cyclohexanecarboxylic acid, 3,5-dinitrosalicylic acid, glutamic acid, histidine, polybutylene phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 2-phosphonobutane-1,2,4-tricarboxylic acid, 5-sulfosalicylic acid and 3-hydroxyphenylphosphorylpropionic acid; (2) The fluorine group-containing compound includes at least one of lithium hexafluorophosphate, fluorinated carbonate, fluorinated phosphate, fluorinated cyclotriphosphazene and fluorinated ether.

3. The positive electrode sheet according to claim 2, wherein: The fluorocarbonate includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoroethyl methyl carbonate and 2,2,2-trifluorodiethyl carbonate.

4. The positive electrode sheet according to any one of claims 2 to 3, wherein: The fluorophosphate ester includes one or more of tris(2,2,2-trifluoroethyl)phosphate, bis(2,2,2-trifluoroethyl)methylphosphate and bis(2,2,2-trifluoroethyl)ethylphosphate.

5. The positive electrode sheet according to any one of claims 2 to 4, wherein: The fluorinated cyclotriphosphazene includes one or more of methoxypentafluorocyclotriphosphazene, trifluoromethoxypentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene and 2,2,2-trifluoroethoxypentafluorocyclotriphosphazene.

6. The positive electrode sheet according to any one of claims 2 to 5, wherein: The fluorinated ether includes one or more of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,1,3,3,3-hexafluoroisopropyl methyl ether.

7. The positive electrode sheet according to any one of claims 1 to 6, wherein: The additive accounts for 5% to 25% by weight of the primer layer.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein: The thickness of the primer layer is ≤4 μm.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein: The first end of the positive electrode current collector is a tab making part for making a tab, and along the length direction, the first end face of the positive electrode active material layer and the first end face of the primer layer are respectively adjacent to the end faces of the tab making part, the distance between the first end face of the primer layer and the end face of the tab making part is recorded as m1, and the distance between the first end face of the positive electrode active material layer and the end face of the tab making part is recorded as m2, 0mm≤m2-m1≤5mm.

10. The positive electrode sheet according to claim 9, wherein: The second end face of the positive electrode active material layer and the second end face of the undercoat layer are respectively far away from the end face of the tab making part, the distance between the second end face of the undercoat layer and the end face of the tab making part is denoted as m3, the distance between the second end face of the positive electrode active material layer and the end face of the tab making part is denoted as m4, the length of the positive electrode active material layer is denoted as L, 0≤m4-m3<L.

11. The positive electrode sheet according to claim 10, wherein: 1 / 3L≤m4-m3<L.

12. The positive electrode sheet according to any one of claims 1 to 11, wherein: The primer layer also contains a conductive agent and a binder; the conductive agent includes one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene and carbon fiber; the binder includes one or more of polyglutamic acid, styrene-butadiene rubber, olefin resin and acrylic resin.

13. The positive electrode sheet according to claim 12, wherein: The conductive agent accounts for 40%-70% by weight in the primer layer, and the binder accounts for 20%-50% by weight in the primer layer.

14. The positive electrode sheet according to any one of claims 1 to 13, wherein: The positive electrode active material layer comprises a positive electrode active material; the positive electrode active material comprises at least one of the following features: (1) The positive electrode active material includes a lithium transition metal oxide having the following chemical formula: Li a Ni b Co c Mn d O2, 0.2<a≤1.2, 0.8≤b≤1, 0≤c≤0.1, 0≤d≤0.1, and b+c+d=1; (2) The volume average particle size Dv50 of the positive electrode active material is ≥3 μm; (3) The positive electrode active material includes one or more of single crystal particles and polycrystalline particles.

15. The positive electrode sheet according to claim 14, wherein: The volume average particle size Dv50 of the positive electrode active material is 5 μm-9 μm.

16. The positive electrode sheet according to any one of claims 1 to 15, wherein: The compaction density of the positive electrode sheet is 3.5 g / cm 3 -3.8g / cm 3 .

17. A secondary battery comprising the positive electrode sheet according to any one of claims 1 to 16.

18. The secondary battery according to claim 17, wherein The secondary battery also includes a negative electrode plate, which contains a negative electrode active material, and the negative electrode active material includes one or more of a silicon-containing material and a carbon-based material; wherein the silicon-containing material includes one or more of silicon oxide and carbon-coated silicon oxide; the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon; the negative electrode active material includes a silicon-containing material and a carbon-based material, and the mass proportion of the silicon-containing material in the negative electrode active material is 3%-12%.

19. The secondary battery according to any one of claims 17 to 18, wherein: The secondary battery further includes an electrolyte, the electrolyte comprising a first lithium salt and a second lithium salt; the first lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate and lithium bis(oxalato)borate, and the second lithium salt comprises one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonylimide; the electrolyte has at least one of the following characteristics: (1) The mass of the first lithium salt accounts for 20% to 70% of the total mass of the first lithium salt and the second lithium salt; (2) The total molar concentration of the first lithium salt and the second lithium salt is 0.5M-1.5M.

20. The secondary battery according to any one of claims 17 to 19, wherein: The energy density of the secondary battery is ≥280Wh / Kg.

21. An electric device comprising the secondary battery according to any one of claims 17 to 20.

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