Positive electrode sheet, secondary battery, and electric device

Abstract

The application relates to a positive electrode sheet, a secondary battery and an electric device, wherein 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 primer layer located between the positive electrode current collector and the positive electrode active material layer; the primer layer comprises an additive, and the additive comprises a compound containing at least one of a carboxylic acid group, a phosphoric acid group and a fluorine group. By arranging the primer layer between the positive electrode current collector and the positive electrode active material layer, the corrosion of the positive electrode current collector by electrolyte can be effectively reduced; and since the additive contained in the primer layer comprises 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, can further play a role in protecting the positive electrode current collector; on the other hand, can also prevent the free aluminum ions from migrating to the negative electrode, so as to avoid the free aluminum ions from damaging the SEI film.

Description

[0001] Related applications

[0002] This application is a divisional application of Chinese patent application No. 2023113308715, filed on October 16, 2023, entitled "Positive electrode sheet, secondary battery and power supply device", the entire contents of which are incorporated herein by reference. Technical Field

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

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. The development of lithium-ion battery technology has led to higher demands on their specific energy. High-energy-density battery designs typically employ a high-nickel combined with a silicon system, using high pressure density and thick coating processes to achieve high energy density. However, high-nickel materials have poor high-temperature stability, are prone to oxygen release at high temperatures, experience rapid lifespan decay, and reduced safety. Adding lithium bis(fluorosulfonyl)imide to the electrolyte can effectively improve storage life and enhance safety. However, high pressure density damages the oxide film on the aluminum foil surface, exposing a fresh aluminum layer. The lithium bis(fluorosulfonyl)imide in the electrolyte will corrode the aluminum foil, causing it to become brittle and break, thus triggering lithium-ion battery safety issues. Summary of the Invention

[0006] This application provides a positive electrode, a secondary battery, and an electrical device to improve the safety of secondary batteries, especially significantly improving the safety of secondary batteries using a high-nickel silicon system.

[0007] To achieve the above objectives, the first aspect of this application provides a positive electrode sheet, comprising:

[0008] Positive current collector;

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

[0010] An undercoat layer, located between the positive electrode current collector and the positive electrode active material layer, comprises an additive, the additive including a compound containing at least one of a carboxylic acid group, a phosphate group, and a fluorine group.

[0011] Therefore, by setting an undercoat layer between the positive electrode current collector and the positive electrode active material layer, the corrosion of the positive electrode current collector by the electrolyte can be effectively reduced. Furthermore, since the additives contained in the undercoat layer include at least one of carboxylic acid groups, phosphate groups, and fluorine groups, these additives can effectively complex and / or capture free aluminum ions. On the one hand, this fixes the free aluminum ions between the positive electrode current collector and the undercoat layer, further protecting the positive electrode current collector; on the other hand, it prevents free aluminum ions from migrating to the negative electrode, avoiding damage to the SEI film by free aluminum ions, thereby improving the safety of the secondary battery.

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

[0013] (1) A compound containing at least one of the carboxylic acid group and the phosphate 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-hydroxyphenylphosphonopropionic 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, methyl ethyl 2,2,2-trifluorocarbonate and diethyl 2,2,2-trifluorocarbonate.

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

[0017] In some embodiments, the fluorocyclic triphosphazene includes one or more of methoxypentafluorocyclic triphosphazene, trifluoromethoxypentafluorocyclic triphosphazene, ethoxypentafluorocyclic triphosphazene, and 2,2,2-trifluoroethoxypentafluorocyclic triphosphazene.

[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-hexafluoroisopropylmethyl ether.

[0019] In some embodiments, the additive accounts for 5%-25% of the mass of the base coating.

[0020] In some embodiments, the thickness of the base coating is ≤4μm.

[0021] In some embodiments, the first end of the positive current collector is a tab-making part for making tabs. Along the length direction, the first end face of the positive active material layer and the first end face of the base layer are respectively adjacent to the end face of the tab-making part. The distance between the first end face of the base layer and the end face of the tab-making part is denoted as m1, and the distance between the first end face of the positive active material layer and the end face of the tab-making part is denoted as m2, where 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 base coating layer are respectively far away from the end face of the tab forming part. The distance between the second end face of the base coating layer and the end face of the tab forming 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 forming part is denoted as m4, and the length of the positive electrode active material layer is denoted as L, where 0 ≤ m4 - m3 < L.

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

[0024] In some embodiments, the base coating further comprises a conductive agent and a binder; the conductive agent includes one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene, and carbon fibers; the binder includes 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% of the mass of the base coating, and the adhesive accounts for 20%-50% of the mass of the base coating.

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

[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 ≥3μm;

[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 / cm³. 3 -3.8 g / cm 3 .

[0032] A second aspect of this application provides a secondary battery including the positive electrode of the first aspect of this application. The safety of the secondary battery including this positive electrode is significantly improved.

[0033] In some embodiments, the secondary battery further includes a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material, the negative electrode active material comprising one or more of silicon-containing materials and carbon-based materials;

[0034] The silicon-containing material includes one or more of silicon suboxide and carbon-coated silicon suboxide; 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 percentage 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 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 dioxolaneborate, and the second lithium salt comprises one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

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

[0037] (1) 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%;

[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 this application provides an electrical device, including a secondary battery as described in the second aspect of this application.

[0041] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0042] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0043] Figure 1 This is a cross-sectional schematic diagram of the positive electrode sheet along the length direction according to an embodiment of this application.

[0044] Figure 2 This is a cross-sectional schematic diagram of the positive electrode sheet along the length direction according to an embodiment of this application.

[0045] Figure 3 This is a schematic diagram of a battery cell according to one embodiment of this application.

[0046] Figure 4 for Figure 3 An exploded view of a battery cell according to one embodiment of this application is shown.

[0047] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0048] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0049] Figure 7 for Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0050] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Electrical device. Detailed Implementation

[0053] Hereinafter, some embodiments of the battery cell, secondary battery, and electrical device of this application are described in detail with appropriate reference to the accompanying drawings. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0054] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0055] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0058] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] In this application, open-ended technical features or solutions described using terms such as "containing," "including," or "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if A includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both the feature or solution that "A consists of a1, a2, and a3" and the feature or solution that "A includes not only a1, a2, and a3, but also other members." In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0060] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0061] In related technologies, high-energy-density battery designs typically employ a high-nickel-silicon system and utilize high-pressure density and thick coating processes to achieve high energy density. Furthermore, lithium bisfluorosulfonylimide is added to the electrolyte. Under the damage to the oxide film on the aluminum foil surface caused by high pressure density, lithium bisfluorosulfonylimide may corrode fresh aluminum foil, leading to safety issues in lithium-ion batteries.

[0062] In addition, due to the large expansion of the silicon system, the pulling effect on the tabs and corners is significant, so the electrolyte may cause more severe corrosion of the aluminum foil at the tabs and corners.

[0063] As compaction density increases, energy density increases, but electrolyte corrosion of the aluminum foil worsens, leading to decreased tensile strength of the positive electrode, deterioration of shallow barbed edges, increased internal resistance, and reduced battery life. Similarly, as silicon content in the negative electrode increases, energy density also increases, but increased negative electrode expansion similarly exacerbates electrolyte corrosion of the aluminum foil, reduces tensile strength of the positive electrode, worsens shallow barbed edges, and reduces battery life. Furthermore, increasing lithium difluorosulfonamide in the electrolyte further worsens electrolyte corrosion of the aluminum foil.

[0064] To address the aforementioned issues, this application provides a positive electrode sheet. By setting an undercoat layer between the positive current collector and the positive active material layer of the positive electrode sheet, the probability of the positive current collector being corroded by the electrolyte can be effectively reduced. Furthermore, the additives in the undercoat layer contain groups that can effectively complex and / or capture aluminum ions, thereby reducing damage to the negative electrode SEI film.

[0065] A first aspect of this application provides a positive electrode sheet, including a positive current collector, a positive active material layer located on at least one side of the positive current collector, and a base coating layer located between the positive current collector and the positive active material layer; the base coating layer includes an additive, the additive including a compound containing at least one group selected from carboxylic acid groups, phosphate groups, and fluorine groups.

[0066] Understandably, by setting an undercoat layer between the positive electrode current collector and the positive electrode active material layer, the corrosion of the positive electrode current collector by the electrolyte can be effectively reduced. Furthermore, since the additives contained in the undercoat layer include at least one of carboxylic acid groups, phosphate groups, and fluorine groups, these additives can effectively complex and / or capture free aluminum ions. On the one hand, this fixes the free aluminum ions between the positive electrode current collector and the undercoat layer, further protecting the positive electrode current collector; on the other hand, it prevents free aluminum ions from migrating to the negative electrode, avoiding damage to the SEI film, thereby improving the safety of the secondary battery.

[0067] In addition, by applying an undercoat, the tensile strength of the electrode can be improved, the discharge discharge rate (DCR) of the secondary battery can be reduced, and the storage life of the secondary battery can be increased.

[0068] As one possible implementation, the compound containing at least one of a carboxylic acid group and a phosphate 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-hydroxyphenylphosphonopropionic acid.

[0069] As one possible implementation, the fluorine-containing compound includes at least one of lithium hexafluorophosphate, fluorocarbonate, fluorophosphate, fluorocyclotriphosphazene, and fluoroether.

[0070] In some alternative embodiments, the fluorocarbonate includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, methyl ethyl 2,2,2-trifluorocarbonate and diethyl 2,2,2-trifluorocarbonate.

[0071] In some alternative embodiments, the fluorophosphate includes one or more of tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, and bis(2,2,2-trifluoroethyl) ethyl phosphate.

[0072] In some alternative embodiments, the fluorocyclic triphosphazene includes one or more of methoxypentafluorocyclic triphosphazene, trifluoromethoxypentafluorocyclic triphosphazene, ethoxypentafluorocyclic triphosphazene, and 2,2,2-trifluoroethoxypentafluorocyclic triphosphazene.

[0073] In some alternative embodiments, the fluoroether comprises 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-hexafluoroisopropylmethyl ether.

[0074] As an example, the types of functional groups and compounds contained in the additives in the aforementioned base coating can be determined using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). The specific method is as follows: Take a small amount of the positive electrode sheet, scrape off the powder, and dry it in a 100℃ oven for 12 hours. Then, determine the presence of a 3500-3300 cm⁻¹ region using an infrared spectrometer. -1 The peak at 1600 cm -1 The presence of a C=O characteristic peak at 288.4 eV was determined by X-ray electron spectroscopy (XPS) to identify the presence of a C=O characteristic peak at 288.4 eV, thus indicating the presence of a carboxylic acid group. The presence of a C=O characteristic peak at 1350-1250 cm⁻¹ was also determined by infrared spectroscopy. -1 The peak at 2700-2200 cm -1 The presence of a hydroxyl characteristic peak at 531.3 eV was determined by X-ray electron spectroscopy (XPS) to identify the presence of a P=O characteristic peak at 531.3 eV, thus determining the presence of a phosphate group. The presence of a phosphate group was also determined by infrared spectroscopy in the 1350-1000 cm⁻¹ region. -1 The presence of a CF bond characteristic peak at 290 eV was determined by X-ray electron spectroscopy (XPS) to identify the presence of a CF bond characteristic peak at 290 eV.

[0075] In some embodiments, the additive constitutes 5%-25% of the primer coating by mass; 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 any two of the above values. When the additive constitutes a portion of the primer coating by mass within the above range, it effectively inhibits the corrosion and dissolution of Al, resulting in a lower DCR and improved lifespan.

[0076] It should be noted that the primer layer also contains conductive agents and binders, and the mass percentages of additives, conductive agents, and binders in the primer layer can be determined simultaneously. As an example, the mass percentages of additives, conductive agents, and binders in the primer layer can be determined using the following method: Take a 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 using microwave high temperature (~200℃) and high pressure (~120 bar) for 6 hours, separating the digestion products into liquid and residue; weigh the residue to obtain the mass m1 of the conductive agent; determine the P and N content in the liquid using inductively coupled plasma optical emission spectrometry (ICP) to deduce the mass m2 of the additive; the mass of the binder is m0 - m1 - m2; further calculate the mass percentages of the additive, conductive agent, and binder in the primer layer separately.

[0077] In some embodiments, the thickness of the undercoating layer is ≤4 μm; for example, it 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 any two of the above values. When the thickness of the undercoating 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.

[0078] As an example, the thickness of the aforementioned base coating can be determined by the following method: take an electrode and measure the thickness of the base coating of the electrode using a cross-sectional polishing-scanning electron microscope (CP-SEM).

[0079] In some embodiments, the first end of the positive current collector is a tab-making part for making tabs. Along the length direction, the first end face of the positive active material layer and the first end face of the base layer are respectively adjacent to the end face of the tab-making part. The distance between the first end face of the base layer and the end face of the tab-making part is denoted as m1, and the distance between the first end face of the positive active material layer and the end face of the tab-making part is denoted as m2, where 0mm≤m2-m1≤5mm.

[0080] Optionally, the second end face of the positive electrode active material layer and the second end face of the base coating layer are respectively far away from the end face of the electrode tab making part. The distance between the second end face of the base coating layer and the end face of the electrode 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 electrode tab making part is denoted as m4, and the length of the positive electrode active material layer is denoted as L, where 0≤m4-m3<L; or optionally 1 / 3L≤m4-m3<L.

[0081] It should be noted that the terms "first end", "first end face" and "second end face" mentioned above are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0082] The m2-m1 mentioned above can be, but is not limited to, 0mm, 0.3mm, 0.5mm, 0.8mm, 1mm, 1.3mm, 1.5mm, 1.7mm, 2mm, 2.3mm, 2.5mm, 2.7mm, 3mm, 3.3mm, 3.5mm, 3.7mm, 4mm, 4.3mm, 4.5mm, 4.7mm, 5mm, or any two of the above values. m2-m1 falling within the above range indicates that, compared to the positive electrode active material layer, the first end face of the undercoating layer is closer to the end face of the tab fabrication portion, which can improve the protective effect of the undercoating layer on the positive electrode current collector.

[0083] The m4-m3 mentioned above can be, but is 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 any 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 bottom coating layer; when 0 < m4-m3 < L, it indicates that the second end face of the bottom coating layer is closer to the end face of the tab fabrication part than the positive electrode active material layer. Usually, the aluminum foil near the tab or corner is more severely corroded by the electrolyte. Therefore, by setting the bottom coating layer at the end face near the tab fabrication part, the corrosion of the positive electrode current collector by the electrolyte can be effectively reduced, and the safety of the secondary battery can be improved.

[0084] Figure 1 This is a schematic cross-sectional view of the positive electrode sheet along its length provided in one embodiment of this application. Figure 1As shown, the base coating 112 is disposed on one surface of the positive current collector 113, and the positive active material layer 111 is disposed on the surface of the base coating 112 away from the positive current collector 113. The base coating 112 does not completely coat the positive current collector 113, and the positive current collector 113 is exposed on at least one side of the base coating 112 to form the tab fabrication part.

[0085] In such Figure 1 In the example shown, the first end face 111a of the positive electrode active material layer 111 and the first end face 112a of the base coating layer 112 are close to the end face 113a of the tab fabrication portion 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 base coating layer 112 are flush.

[0086] Figure 2 This is a cross-sectional schematic diagram of the positive electrode sheet along its length, provided for another embodiment of this application. Figure 2 The example shown is the same as Figure 1 They are basically the same, with the main difference being that the positive electrode active material layer 211 is not entirely located on the base coating layer 212; part of it is located on the base coating layer 212, and part of it is in direct contact with the positive electrode current collector 213. The positive electrode current collector 213 is exposed on one side of the base coating layer 212, forming the tab fabrication section.

[0087] In such Figure 2 In the example shown, the first end face 211a of the positive electrode active material layer 211 and the first end face 212a of the base coating layer 212 are close to the end face 213a of the tab forming part of the positive electrode current collector 213, and the second end face 212b of the base coating layer 212 is closer to the end face 213a of the tab forming part of the positive electrode current collector 213 than the second end face 211b of the positive electrode active material layer 211.

[0088] The "length direction" mentioned above refers to the method from one side of the positive current collector where the tab is fabricated 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 of the positive current collector, the positive active material layer, and the base coating layer, and are not used to limit the positive electrode sheet; for descriptive purposes, "width" and "width direction" may also be used accordingly, and there is no specific limitation.

[0089] In some embodiments, the primer layer also includes a conductive agent and a binder.

[0090] In some alternative embodiments, the conductive agent includes one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0091] In some alternative embodiments, the binder includes one or more of polyglutamic acid, styrene-butadiene rubber, olefin resins, and acrylic resins.

[0092] In some optional embodiments, the conductive agent constitutes 40%-70% of the primer coating by mass; for example, it can be, but is not limited to, 40%, 43%, 45%, 48%, 50%, 52%, 55%, 57%, 60%, 63%, 65%, 68%, 70%, or any two of the above values. When the conductive agent constitutes a portion of the primer coating by mass within the above range, it improves the conductivity of the primer coating while also facilitating the effectiveness of additives in the primer coating.

[0093] In some optional embodiments, the binder comprises 20%-50% by mass in 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 any two of the above values. When the mass percentage of the binder in the primer layer is within the above range, it facilitates the uniform dispersion of conductive agents and additives in the primer layer, and enables the primer layer to have both strong adhesion and good conductivity.

[0094] In some embodiments, the positive electrode active material layer comprises a positive electrode active material.

[0095] In some alternative embodiments, the positive electrode active material comprises a lithium transition metal oxide having the following chemical formula: Li a (A b Co c Mn d Al e O2, wherein 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;

[0096] Optionally, the positive electrode active material comprises 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.

[0097] It should be noted that the above limitation on 'a' includes the molar content of Li under different charge and discharge states of the battery (typically the battery voltage is between 2-5V).

[0098] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. Unless otherwise specified, the Li content in the examples of positive electrode materials listed in this application refers to the initial state of the material. When a positive electrode material is applied to a positive electrode in a battery system, the Li content in the positive electrode material typically changes after charge-discharge cycles. The Li content can be measured using molar content, but is not limited to this. Regarding "Li content refers to the initial state of the material," the initial state of the material refers to its state before being added to the positive electrode slurry. It is understood that new materials obtained by appropriately modifying the listed positive electrode materials are also within the scope of positive electrode materials. The aforementioned appropriate modification refers to acceptable modification methods for the positive electrode material; non-limiting examples include coating modification.

[0099] In the examples of cathode materials in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in molar content, but is not limited to this.

[0100] In some embodiments, the positive electrode active material may also be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may also include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries 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 include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. 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 known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM)523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0101] In some optional embodiments, the volume average particle size Dv50 of the positive electrode active material is ≥3μm, and can be selected as 5μm-9μm; for example, it can be, but is not limited to, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm or any two of the above values.

[0102] As an example, the volume average particle size Dv50 of the aforementioned positive electrode active material can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0103] In some alternative embodiments, the positive electrode active material includes one or more of monocrystalline and polycrystalline particles. Using a positive electrode active material that simultaneously comprises monocrystalline 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.

[0104] 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 substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0105] In some embodiments, the positive electrode active material layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0106] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, 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.

[0107] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as additives, conductive agents, and binders used to prepare the base coating, in water to form a base coating slurry; coating the base coating slurry onto at least one surface of the positive electrode current collector and drying it to obtain the base coating layer; then dispersing the positive electrode active material, conductive agent, binder, and any other components used to prepare the positive electrode active material layer in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto the surface of the base coating layer, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the base coating 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 base coating slurry can be 20wt%-30wt%. The viscosity of the base coating slurry at room temperature can be adjusted to 1500-3000 mPa·s. The solid content of the cathode slurry can be 40wt%-80wt%. The viscosity of the cathode slurry at room temperature can be adjusted to 5000-25000 mPa·s.

[0108] In some embodiments, the compaction density of the positive electrode sheet is ≥3.5 g / cm³. 3 3.5g / cm³ is an option. 3 -3.8g / cm 3 For example, it can be, but is not limited to, 3.5 g / cm³. 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.

[0109] As an example, the compaction density of the aforementioned positive electrode sheet can be 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 current collector, and then calculate the compaction density PD=m / Sd of the positive electrode sheet.

[0110] A second aspect of this application provides a secondary battery, including the positive electrode of the first aspect. The safety of the secondary battery including this positive electrode is significantly improved.

[0111] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0112] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte in the electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0113] In some embodiments, the secondary battery further includes a negative electrode sheet containing a negative electrode active material, which includes one or more of silicon-containing materials and carbon-based materials. The inclusion of silicon-containing materials in the negative electrode active material, i.e., introducing a silicon system into the negative electrode sheet, can improve the energy density of the negative electrode sheet. Combined with the use of high-nickel materials as the positive electrode active material, the energy density of the secondary battery can reach 280Wh / Kg or higher.

[0114] In some alternative embodiments, the silicon-containing material includes one or more of silicon suboxide and carbon-coated silicon suboxide.

[0115] In some alternative implementations, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0116] In some optional embodiments, the negative electrode active material includes silicon-containing materials and carbon-based materials, with the silicon-containing material accounting for 3%-12% of the mass of the negative electrode active material; 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 any two of the above values. When the mass percentage of silicon-containing material in the negative electrode active material is within the above range, it can meet the high capacity requirements while avoiding electrode breakage due to the expansion of the silicon-containing material.

[0117] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0118] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0119] In some embodiments, the negative electrode active material may also be a known battery negative electrode active material. 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, etc. Silicon-based materials may include one or more of elemental silicon, silicon-nitrogen compounds, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0120] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0121] In some embodiments, the negative electrode active material layer may optionally 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).

[0122] In some embodiments, the negative electrode active material layer may optionally include other conductive agents known in the art for use in negative electrode sheets. The conductive agents may include one or more of superconducting carbon, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0123] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0124] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, hierarchical porous carbon nanotubes, a second conductive agent, a binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of a negative electrode current collector, and then drying, cold pressing, etc., to obtain the negative electrode sheet. 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 both 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 2000-10000 mPa·s. The compacted density of the negative electrode sheet can be 1.0 g / cm³. 3 -1.8 g / cm 3 .

[0125] In some embodiments, the secondary battery further includes an electrolyte comprising a first lithium salt and a second lithium salt; the first lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium dioxalate borate, and the second lithium salt includes one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. The simultaneous inclusion of both the first and second lithium salts in the electrolyte improves the stability of the electrolyte system and reduces corrosion to the substrate.

[0126] In some optional embodiments, the mass percentage of the first lithium salt to the total mass of the first and second lithium salts 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 any two of the above values. When the mass percentage of the first lithium salt to the total mass of the first and second lithium salts is within the above range, the stability of the electrolyte system can be improved while corrosion of the substrate can be reduced.

[0127] In some alternative 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 any two of the above values.

[0128] As an example, the percentage of the mass of the first lithium salt relative to the total mass of the first and second lithium salts, and the total molar concentration of the first and second lithium salts, can be determined by the following method: take an electrolyte sample, evaporate the solvent, and determine the content of characteristic elements (P, B, F) of the first lithium salt and characteristic elements (N, S) of the second lithium salt in the electrolyte using an inductively coupled plasma optical emission spectrometer (ICP). Then, calculate the percentage of the mass of the first lithium salt relative to the total mass of the first and second lithium salts, and the total molar concentration of the first and second lithium salts.

[0129] In some implementations, the energy density of the secondary battery is ≥280Wh / Kg.

[0130] 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 difluorooxalate borate (LiDFOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The electrolyte functions as a conductor of ions between the positive and negative electrodes.

[0131] In some embodiments, the solvent in the electrolyte may include ethylene carbonate (EC). ), propylene carbonate (PC, ), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethylene carbonate ( One or more of the following: 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.

[0132] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0133] 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), trifluoromethyl ethylene carbonate (TFPC), etc.

[0134] Separating membrane

[0135] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0136] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven 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.

[0137] In some embodiments, the thickness of the isolation membrane is 6 μm-40 μm, optionally 12 μm-20 μm.

[0138] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0139] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0140] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0141] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0142] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0143] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 The example shown is a square-structured battery cell 5.

[0144] In some of these embodiments, reference is made to Figure 4The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0145] Secondary batteries can be battery modules or battery packs.

[0146] A battery module includes at least one battery cell. The number of battery cells 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.

[0147] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0148] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0149] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0150] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] In addition, this application also provides an electrical device, which includes at least one of the battery cell and secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may 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.

[0152] As an electrical device, you can choose between single-cell batteries or rechargeable batteries depending on your usage requirements.

[0153] Figure 8 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0154] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0155] Example

[0156] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0157] Preparation of primary and secondary batteries

[0158] Example 1

[0159] 1. Preparation of positive electrode sheet

[0160] 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 uniformly coated on both sides of the aluminum foil and dried to obtain an aluminum foil with a primer coating.

[0161] LiNi 0.95 Co 0.03 Mn 0.02O2 (as the positive electrode active material), acetylene black (as a conductive agent), and polyvinylidene fluoride (PVDF, as a binder) were dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 96.5:1.5:2. After thorough mixing, a positive electrode slurry was obtained. The positive electrode slurry was then uniformly coated onto an aluminum foil with a base coating. After drying, cold pressing, and slitting, the positive electrode sheet was obtained. The thickness of the base coating in the positive electrode sheet was measured to be 1 μm, and the compaction density of the positive electrode sheet was 3.5 g / cc.

[0162] 2. Preparation of negative electrode sheet

[0163] The active material graphite, silicon suboxide, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water in a weight ratio of 90:5:2:2:1 and mixed evenly to prepare a negative electrode slurry. The slurry is then coated on both sides of a copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0164] 3. Diaphragm

[0165] It uses a PE diaphragm with a PVDF and alumina coating on the surface to improve adhesion and heat resistance.

[0166] 4. Electrolyte

[0167] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. Then, LiPF6:LiFSI (2:8) was uniformly dissolved in the above solution to obtain an electrolyte. The concentration of lithium salt in the electrolyte was 1 mol / L.

[0168] The positive electrode, separator, and negative electrode are stacked in sequence. The separator acts as a barrier between the positive and negative electrodes. The cells are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is randomly injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to produce a lithium-ion battery.

[0169] Example 2-19

[0170] The preparation methods of the secondary batteries in Examples 2-19 are basically the same as those in Example 1, with the main differences being at least one of the following: the thickness of the base coating, the mass ratio of the additives in the base coating, and the type of additives. See Table 1 for details.

[0171] It should be noted that in the bottom coating of the positive electrode sheet in Example 7, the mass ratio of the conductive agent is 50% and the mass ratio of the binder is 20%.

[0172] In Example 8, the conductive agent in the bottom coating of the positive electrode sheet accounts for 60% by mass, and the binder accounts for 20% by mass.

[0173] In Example 9, the conductive agent in the bottom coating of the positive electrode sheet accounts for 40% by mass, and the binder accounts for 50% by mass.

[0174] In Example 10, the conductive agent in the bottom coating of the positive electrode sheet accounts for 70% by mass, and the binder accounts for 25% by mass.

[0175] In Example 11, the conductive agent in the bottom coating of the positive electrode sheet accounts for 50% by mass and the binder accounts for 47% by mass.

[0176] In Example 12, the conductive agent in the bottom coating of the positive electrode sheet accounts for 40% by mass, and the binder accounts for 50% by mass.

[0177] Comparative Example 1

[0178] The main difference between the preparation method of the secondary battery in Comparative Example 1 and the preparation method of the secondary battery in Example 1 is that only conductive agent and binder are added to the primer slurry, and no additives are added; the mass ratio of conductive agent to binder is 7:3; all other aspects are the same. See Table 1 for details.

[0179] Comparative Example 2

[0180] The difference between the preparation method of the secondary battery in Comparative Example 2 and that in Comparative Example 1 is that no bottom coating was prepared in the positive electrode sheet; all other aspects are the same. See Table 1 for details.

[0181] Comparative Example 3

[0182] The difference between the preparation method of the secondary battery in Comparative Example 3 and that in Comparative Example 2 is that the ratio of LiPF6:LiFSI in the electrolyte is 7:3, while all other aspects are the same. See Table 1 for details.

[0183] Comparative Example 4

[0184] 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 ratio of silicon suboxide in the active material layer of the negative electrode is 20%, while all other aspects are the same. See Table 1 for details.

[0185] Comparative Example 5

[0186] The difference between the preparation method of the secondary battery in Comparative Example 5 and that in Comparative Example 2 is that silicon oxide was not added to the active material layer of the negative electrode; instead, graphite of the same mass was used to replace silicon suboxide. See Table 1 for details.

[0187] Comparative Example 6

[0188] The difference between the preparation method of the secondary battery in Comparative Example 6 and that in Comparative Example 5 is that the compaction density of the positive electrode sheet is 3.6 g / cc, while all other aspects are the same. See Table 1 for details.

[0189] Comparative Example 7

[0190] 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, while all other aspects are the same. See Table 1 for details.

[0191] Comparative Example 8

[0192] 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 that the types of additives are different; everything else is the same. See Table 1 for details.

[0193] The structural parameters of the secondary batteries in the above embodiments and comparative examples are shown in Table 1.

[0194] Table 1

[0195]

[0196] Where w1 represents the mass percentage of the additive in the base coating, w2 represents the mass percentage of silicon-containing materials in the negative electrode active material, w3 represents the mass percentage of LiFSI in the total lithium salt in the electrolyte, d represents the thickness of the base coating, cd represents the compaction density of the positive electrode sheet, and FEC represents fluoroethylene carbonate.

[0197] It should be noted that the thickness of the bottom coating in the positive electrode mentioned above was determined by the following method: take the positive electrode and measure the thickness of the bottom coating of the positive electrode by cross-sectional polishing-scanning electron microscopy (CP-SEM).

[0198] The compaction density of the aforementioned positive electrode sheet was determined using the following method: a circular positive electrode sheet with a diameter of 14 mm was taken, the area S of the positive electrode sheet was calculated, its thickness d was measured, and the weight m of the active material layer excluding the positive current collector was weighed, thereby calculating the compaction density PD = m / Sd of the positive electrode sheet.

[0199] II. Secondary Battery Performance Testing

[0200] 1. Shallow prick test

[0201] The secondary batteries in the above embodiments and comparative examples were discharged to 2.8V at 25°C at a rate of 1 / 3C, left to stand for 60 minutes, charged to 4.25V at a rate of 1 / 3C, and kept at a constant voltage until 0.05C was reached. After standing for 60 minutes, part of the casing was removed, and the voltage, internal resistance, and weight of the battery cell were recorded at this time.

[0202] A nail penetration test was conducted at 25℃. The nail diameter was 1 mm, the speed was 0.1 mm / s, and the nail was inserted at a constant speed perpendicular to the direction of the battery plate, with the insertion position close to the geometric center of the punctured surface. The insertion depth was 4 mm, and the voltage drop was monitored. The test was observed for 1 hour. If there was no failure, the insertion depth was changed to 5 mm, and the above steps were repeated until failure occurred. The voltage, internal resistance, and weight of the cell at the time of failure were recorded, and the results are shown in Table 2.

[0203] 2. Storage Days Test

[0204] The secondary batteries in the above embodiments and comparative examples were stored at 60℃ and 97% SOC, respectively. Before and during storage, the initial reversible capacity and actual reversible capacity of the cells were recorded for C0 and Cn, respectively. The batteries were tested every 15 days. The testing process was as follows: Each secondary battery was left to stand at 25℃ for 30 minutes, charged at a rate of 1 / 3C to 4.25V, kept constant at 0.05C, left to stand for 30 minutes, and then discharged at a rate of 1 / 3C to 2.8V. The initial reversible capacity C0 was recorded. Testing was conducted every 15 days, and Cn was recorded (n=1, 2, 3, 4, 5…). When Cn / C0 ≤ 80%, n was recorded. The EOL storage days = 15 * n. The results are shown in Table 2.

[0205] 3. Tensile strength test

[0206] During the tensile process of the positive electrode sheet, after the material passes through the yielding stage and enters the strengthening stage, the cross-sectional dimensions of the material decrease significantly. The maximum force (Fb) that the material can withstand at the point of fracture is divided by the original cross-sectional area (So) of the specimen, resulting in stress (σ). This stress is called the tensile strength or ultimate tensile strength, and its unit is N / m2 (or MPa). It represents the maximum ability of a metallic material to resist fracture under tensile force, as shown in Table 2.

[0207] The formula for calculating tensile strength is: σ = Fb / So

[0208] In the formula: Fb represents the maximum force that the specimen can withstand when it breaks, N (Newtons); So represents the original cross-sectional area of ​​the specimen, mm².

[0209] The performance test results of the above embodiments and comparative examples are shown in Table 2.

[0210] Table 2

[0211]

[0212] As can be seen from the comparison of the results of Examples 1-19 and Comparative Examples 1-8, the positive electrode sheet provided in this application has high tensile strength, and can improve the storage life of the secondary battery and enhance the safety of the secondary battery.

[0213] The main difference between Examples 1-6 lies in the thickness of the undercoating layer. Example 6 has the thickest undercoating layer. A comparison of the results from Examples 1-6 shows that when the undercoating layer thickness is ≤4μm, the positive electrode exhibits higher tensile strength and deeper shallow burr depth, resulting in a longer cycle life for the secondary battery. This indicates that when the undercoating layer thickness is ≤4μm, it effectively prevents electrolyte corrosion of the current collector while simultaneously improving the tensile strength and cycle life of the positive electrode, thus enhancing the safety of the secondary battery.

[0214] The main difference between Example 2 and Examples 7-11 is that the mass percentage of the additive in the base coating is different; the mass percentage of the additive is the largest in Example 7 and the mass percentage of the additive is the smallest in Example 11. A comparison with the results of Examples 7 and 7-11 shows that when the mass percentage of the additive in the base coating is 5%-25%, it can protect the current collector from corrosion by the electrolyte while also improving the tensile strength and shallow burr depth of the positive electrode and the storage life of the secondary battery.

[0215] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0216] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode and an electrolyte, wherein the positive electrode includes: Positive current collector; A positive electrode active material layer is located on at least one side of the positive electrode current collector; and An undercoating layer is located between the positive electrode current collector and the positive electrode active material layer. The undercoating layer contains an additive, which includes a compound containing at least one group selected from carboxylic acid groups, phosphate groups, and fluorine groups. The electrolyte comprises a first lithium salt and a second lithium salt; the first lithium salt comprises one or more of lithium hexafluorophosphate, lithium tetrafluoroborate and lithium dioxalate borate, and the second lithium salt comprises one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

2. The secondary battery as described in claim 1, characterized in that, The additive has at least one of the following characteristics: (1) A compound containing at least one of the carboxylic acid group and the phosphate 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-hydroxyphenylphosphonopropionic acid; (2) The compounds containing the fluorine group include at least one of lithium hexafluorophosphate, fluorocarbonate, fluorophosphate, fluorocyclotriphosphazene and fluoroether.

3. The secondary battery as described in claim 2, characterized in that, The fluorocarbonate includes one or more of the following: fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, methyl ethyl 2,2,2-trifluorocarbonate and diethyl 2,2,2-trifluorocarbonate.

4. The secondary battery as described in claim 2, characterized in that, The fluorophosphates include one or more of tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, and bis(2,2,2-trifluoroethyl) ethyl phosphate.

5. The secondary battery as described in claim 2, characterized in that, The fluorocyclic triphosphazene includes one or more of methoxypentafluorocyclic triphosphazene, trifluoromethoxypentafluorocyclic triphosphazene, ethoxypentafluorocyclic triphosphazene, and 2,2,2-trifluoroethoxypentafluorocyclic triphosphazene.

6. The secondary battery as described in claim 2, characterized in that, The fluoroethers include 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-hexafluoroisopropylmethyl ether.

7. The secondary battery according to any one of claims 1 to 6, characterized in that, The additive accounts for 5%-25% of the mass of the base coating.

8. The secondary battery according to any one of claims 1 to 7, characterized in that, The thickness of the base coating is ≤4μm.

9. The secondary battery according to any one of claims 1 to 8, characterized in that, The first end of the positive current collector is the tab-making part for making tabs. Along the length direction, the first end face of the positive active material layer and the first end face of the base coating layer are respectively adjacent to the end face of the tab-making part. The distance between the first end face of the base coating layer and the end face of the tab-making part is denoted as m1, and the distance between the first end face of the positive active material layer and the end face of the tab-making part is denoted as m2. 0mm≤m2-m1≤5mm.

10. The secondary battery as described in claim 9, characterized in that, The second end face of the positive electrode active material layer and the second end face of the base coating layer are respectively away from the end face of the tab forming part. The distance between the second end face of the base coating layer and the end face of the tab forming 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 forming part is denoted as m4, and the length of the positive electrode active material layer is denoted as L, where 0 ≤ m4 - m3 < L.

11. The secondary battery as described in claim 10, characterized in that, 1 / 3L≤m4-m3<L.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The base coating also includes a conductive agent and a binder; the conductive agent includes one or more of carbon black, graphite, Ketjen black, carbon nanotubes, graphene, and carbon fibers; the binder includes one or more of polyglutamic acid, styrene-butadiene rubber, olefin resins, and acrylic resins.

13. The secondary battery as described in claim 12, characterized in that, The conductive agent accounts for 40%-70% of the mass of the base coating, and the adhesive accounts for 20%-50% of the mass of the base coating.

14. The secondary battery according to any one of claims 1 to 13, characterized in that, The positive electrode active material layer comprises a positive electrode active material; the positive electrode active material includes at least one of the following characteristics: (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 ≥3μm; (3) The positive electrode active material includes one or more of single crystal particles and polycrystalline particles.

15. The secondary battery as described in claim 14, characterized in that, The volume average particle size Dv50 of the positive electrode active material is 5μm-9μm.

16. The secondary battery according to any one of claims 1 to 15, characterized in that, The positive current collector includes aluminum or an aluminum alloy.

17. The secondary battery according to any one of claims 1 to 16, characterized in that, The compaction density of the positive electrode sheet is 3.5 g / cm³. 3 -3.8 g / cm 3 .

18. The secondary battery according to any one of claims 1 to 17, characterized in that, The secondary battery further includes a negative electrode sheet, which contains a negative electrode active material, including one or more of silicon-containing materials and carbon-based materials; wherein the silicon-containing material includes one or more of silicon suboxide and carbon-coated silicon suboxide; and the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

19. The secondary battery as described in claim 18, characterized in that, The negative electrode active material includes silicon-containing materials and carbon-based materials, and the silicon-containing materials account for 3%-12% of the mass of the negative electrode active material.

20. The secondary battery according to any one of claims 1 to 19, characterized in that, The electrolyte has at least one of the following characteristics: (1) 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%, and can be selected as 20%-30%; (2) The mass percentage of the second lithium salt to the total mass of the first lithium salt and the second lithium salt is 30%-80%, and can be selected as 70%-80%; (3) In the electrolyte, the total molar concentration of the first lithium salt and the second lithium salt is 0.5M-1.5M.

21. The secondary battery according to any one of claims 1 to 20, characterized in that, The energy density of the secondary battery is ≥280Wh / Kg.

22. An electrical appliance, characterized in that, Includes the secondary battery as described in any one of claims 1 to 21.

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