Positive pole piece, battery and electric equipment

Abstract

The invention discloses a positive pole piece, a battery and electric equipment, the positive pole piece comprises a positive active material layer, the positive active material layer comprises a first positive active material layer and a second positive active material layer, the second positive active material layer is located at the outer side of the first positive active material layer, and the second positive active material layer comprises a second positive active material; wherein the proportion of the thickness of the first positive electrode active material layer in the total thickness of the positive electrode active material layer is H, and the unit is%; the lattice volume shrinkage rate of the second positive electrode active material is V, and the unit is%; v and H satisfy the following relation. According to the positive electrode plate, the ratio of the lattice shrinkage rate of the positive electrode active material on the outer side to the thickness ratio of the active material layer on the inner side is regulated and controlled to meet a certain range, so that the adjacent active material layers have relatively matched charging and discharging capacities, and the improvement of the cycling stability is facilitated.

Description

[0001] This application is a divisional application of the application filed on July 11, 2023, with application number 202310847346.4 and the invention title "Positive electrode sheet, battery and electrical device". Technical Field

[0002] This application relates to the field of battery technology, and more specifically, to a positive electrode, a battery, and an electrical device. Background Technology

[0003] With increasing demands for energy density and stability, some technical solutions propose using layered positive electrode active materials with different properties. However, the charge-discharge capabilities of the layered active material layers are often poorly matched, affecting cycle stability. Summary of the Invention

[0004] In view of the above problems, this application provides a positive electrode sheet, a battery and an electrical device, wherein the charge and discharge capabilities of the layered active material layers are well matched, which can improve cycle stability.

[0005] The embodiments of this application are implemented as follows: In a first aspect, embodiments of this application provide a positive electrode sheet, which includes a positive electrode active material layer. The positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, with the second positive electrode active material layer located outside the first positive electrode active material layer. The second positive electrode active material layer includes a second positive electrode active material. The thickness of the first positive electrode active material layer accounts for H (in %) of the total thickness of the positive electrode active material layer. The lattice volume shrinkage rate of the second positive electrode active material is V (in %). The relationship between V and H satisfies: .

[0006] In the technical solution of this application embodiment, the ratio between the lattice shrinkage rate of the outer positive electrode active material and the thickness ratio of the inner active material layer is adjusted to meet a certain range, so that the adjacent active material layers have a better matching charge and discharge capability, which is beneficial to improving cycle stability.

[0007] In some embodiments, V and H satisfy the following relationship: .

[0008] In these embodiments, the ratio of V value to H value meets a further range, so that adjacent active material layers have a more matched charge and discharge capability, which is beneficial to improve cycle stability.

[0009] In some embodiments, the value of V satisfies: 2% ≤ V ≤ 4%; alternatively, the value of V satisfies: 2% ≤ V ≤ 3%.

[0010] In these embodiments, the second positive electrode active material has a small lattice shrinkage rate, which is beneficial for improving the phenomenon of cracking and breakage of the second positive electrode active material; at the same time, it is beneficial for controlling the ratio of V value to H value within a suitable range, which can improve cycle stability. In addition, under the condition of satisfying this V value, there are more ternary positive electrode materials (such as nickel-cobalt-manganese ternary materials) to choose from, which is beneficial for improving energy density.

[0011] In some embodiments, the value of H satisfies: 14% ≤ H ≤ 61%; alternatively, the value of H satisfies: 14% ≤ H ≤ 39%.

[0012] In these embodiments, the thickness ratio of the inner active material layer meets a certain range. When the ratio requirement of V value and H value is met, the V value can meet a suitable range, which is beneficial to improving cycle stability. At the same time, it is beneficial to better match the first positive electrode active material layer and the second positive electrode active material layer and perform their respective functions. When the first positive electrode active material in the first positive electrode active material layer includes a highly stable lithium phosphate, the thickness ratio of the first positive electrode active material layer is above a certain standard, which also enables the first positive electrode active material layer to have a certain charge and discharge capability, which is beneficial to improving cycle stability.

[0013] In some embodiments, the first positive electrode active material layer includes a first positive electrode active material, and the specific surface area BET of the first positive electrode active material satisfies: 7 m² 2 / g≤BET≤24m 2 / g; Optionally, BET satisfies: 9m 2 / g≤BET≤22m 2 / g.

[0014] In these embodiments, the specific surface area (BET) of the first positive electrode active material is above a certain standard, giving it good electrochemical activity; the specific surface area (BET) of the first positive electrode active material is below a certain standard, which can improve the deterioration of cycle stability caused by water absorption of the material.

[0015] In some embodiments, the first positive electrode active material layer includes a first positive electrode active material, which includes a doped or undoped lithium phosphate; and / or the second positive electrode active material includes a ternary positive electrode material.

[0016] In these embodiments, lithium phosphate has good stability, and ternary cathode materials have high energy density, which is beneficial for balancing good cycle stability and energy density.

[0017] In some embodiments, lithium phosphates include Li 1+x Mn 1-y A y P 1-z E zO4, -0.100 ≤ x ≤ 0.100, 0.001 ≤ y ≤ 0.500, 0.001 ≤ z ≤ 0.100, element A comprises one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb or Ge; element E comprises one or more of B, Si, N, S, F, Cl or Br; and / or the ternary cathode material comprises Li a Ni b Co c M1 d M2 e O f R g , 0.75 ≤ a ≤ 1.2, 0.4 < b < 0.7, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, element M1 comprises Mn and / or Al, element M2 comprises one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb, element R comprises one or more of N, F, S or Cl.

[0018] In these embodiments, the lithium-containing phosphate has good electrochemical performance, such as good stability.

[0019] In these embodiments, the ternary cathode material has good electrochemical performance, such as high energy density, appropriate lattice shrinkage rate, etc.

[0020] In some embodiments, the lithium-containing phosphate comprises Fe element, and the ternary cathode material comprises Mn element; in the positive electrode active material layer, the mass ratio of Fe element to Mn element is 0.03 - 0.25; optionally, the mass ratio of Fe element to Mn element is 0.05 - 0.20.

[0021] In these embodiments, the mass ratio of Fe element to Mn element satisfies a certain range, which is beneficial to regulating the H value within an appropriate range, thereby better improving the cycle stability.

[0022] In some embodiments, the positive electrode active material further comprises at least one coating layer coated on at least a part of the surface of the first positive electrode active material and / or the second positive electrode active material, wherein the coating layer comprises one or more of oxides, nitrates, phosphates or carbonates containing specified elements, and the specified elements comprise one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B or P; and / or the coating layer comprises one or more of pyrophosphates, phosphates or carbon.

[0023] In these embodiments, the coating layer can modify the positive electrode active material.

[0024] In some embodiments, the positive electrode further includes a hydrophobic conductive layer located between the first positive electrode active material layer and the second positive electrode active material layer, and the hydrophobic conductive layer includes a hydrophobic conductive material.

[0025] In these embodiments, the hydrophobic conductive layer has both hydrophobic and conductive functions. The conductive function enables the first positive electrode active material layer and the second positive electrode active material layer to maintain good conductivity, while the hydrophobic function helps to improve cycle stability.

[0026] In some embodiments, the hydrophobic conductive material includes a hydrophobic conductive polymer and a hydrophobic conductive carbon.

[0027] In these embodiments, the combination of hydrophobic conductive polymer and hydrophobic conductive carbon can provide good conductivity and hydrophobicity.

[0028] In some embodiments, the hydrophobic conductive polymer includes one or more of polypyrrole, polyaniline, polythiophene, or polyacetylene; and / or the hydrophobic conductive carbon includes one or more of hydrophobic carbon nanotubes or hydrophobic carbon nanofibers.

[0029] In these embodiments, the hydrophobic conductive polymer and the hydrophobic conductive carbon are suitable choices that can well meet the performance requirements for hydrophobic conductive materials.

[0030] In some embodiments, the mass percentage of hydrophobic conductive carbon in the hydrophobic conductive material is 2% to 10%.

[0031] In these embodiments, the hydrophobic conductive carbon has a suitable mass ratio in the hydrophobic conductive material, which enables the performance requirements of the hydrophobic conductive material to be well met.

[0032] Secondly, embodiments of this application provide a battery including the positive electrode sheet of the above embodiments.

[0033] Thirdly, embodiments of this application provide an electrical device including the battery described in the above embodiments.

[0034] The above description is merely an overview of the technical solutions of the embodiments of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are described below. Attached Figure Description

[0035] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments; Figure 2 Exploded views of batteries provided for some embodiments of this application; Figure 3 Exploded views of a single battery cell provided in some embodiments of this application; Figure 4 This is a schematic diagram of the structure of a first type of positive electrode sheet provided in some embodiments of this application; Figure 5 This is a schematic diagram of the structure of a second type of positive electrode sheet provided in some embodiments of this application.

[0037] icon: 1000 - Vehicles; 100 - Battery; 200 - Controller; 300 - Motor; 10-Box body; 11-First part; 12-Second part; 13-Accommodation space; 20-Battery cell; 21-Casing; 22-Electrode assembly; 23-Electrode terminal; 24-Pressure relief structure; 211-Shell; 212-Cover; 213-Sealed space; 221-Positive electrode sheet; 2211-Positive current collector; 2212-Positive active material layer; 2212a-First positive active material layer; 2212b-Second positive active material layer; 2213-Hydrophobic conductive layer; A - The thickness direction of the positive electrode sheet. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] In the description of the embodiments of this application, the technical terms "first", "second", etc. are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0042] In the description of the embodiments of this application, the technical terms "and / or", such as "feature 1 and / or feature 2", all refer to "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2". In addition, the character " / " in this document generally indicates that the objects before and after it are in an "or" relationship.

[0043] In the description of the embodiments of this application, unless otherwise stated, "multiple" in "one or more" means two or more.

[0044] 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 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.

[0045] In the embodiments of this application, the same reference numerals denote the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments. It should be understood that the height, length, width, and other dimensions of various components in the embodiments of this application shown in the accompanying drawings, as well as the overall height, length, width, and other dimensions of the integrated device, are merely illustrative and should not constitute any limitation on this application.

[0046] From a market perspective, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of the application areas of power batteries, the market demand is also constantly increasing.

[0047] In the manufacturing process of lithium-ion secondary battery electrode sheets, single-layer coating is typically used, where the required active material is coated onto the current collector in a single layer. With increasing demands for energy density and stability, some technical solutions propose using a combination of positive electrode active materials with different properties in a layered manner. For example, positive electrode active materials with high energy density (such as ternary materials) and positive electrode active materials with high stability (such as lithium phosphate) can be used in a layered manner to balance energy density and stability.

[0048] During cycling, the active material on the outer side of the positive electrode active material layer, being closer to the negative electrode, experiences easier lithium insertion / extraction reactions. The actual degree of lithium insertion / extraction due to these reactions is greater than the apparent degree (e.g., the apparent charge / discharge voltage range is 2.5V~4.4V, while the actual range is 2.45V~4.45V). This wider charge / discharge range leads to greater volume changes in the active material, which can easily cause cracks and breakage, thus affecting cycle stability.

[0049] Lattice shrinkage can regulate volume change; materials with smaller lattice shrinkage exhibit smaller volume changes, which can mitigate cracking and breakage of the outer active material. However, materials with smaller lattice shrinkage also have poor rate performance and are less compatible with adjacent active material layers, thus affecting cycle stability.

[0050] While the mechanism of coating multiple active material layers is not entirely clear, the inventors of this application have discovered that, given a fixed type of active material, when the rate performance of the active material decreases, the active material layer needs to have a larger proportion within the multilayer active material layer to achieve a more compatible charge / discharge capability with adjacent active material layers. This results in better matching between the active material layers, which is beneficial for improving cycle stability. In other words, given a fixed type of active material on the inner and outer sides, when the lattice shrinkage rate of the outer active material increases, its rate performance improves, requiring a decrease in the thickness proportion of the outer active material layer, correspondingly requiring an increase in the thickness proportion of the inner active material layer; conversely, the same logic applies.

[0051] Based on this, this application provides a positive electrode sheet, wherein the ratio between the lattice contraction rate of the outer positive electrode active material and the thickness ratio of the inner active material layer is adjusted to meet a certain range. That is, when the lattice contraction rate of the outer positive electrode active material increases, the inner active material layer has a relatively larger thickness ratio, and when the lattice contraction rate of the outer positive electrode active material decreases, the inner active material layer has a relatively smaller thickness ratio, so that the adjacent active material layers have a more matched charge and discharge capability, which is beneficial to improving cycle stability.

[0052] The battery cell using the positive electrode disclosed in this application can be used, but is not limited to, in electrical devices such as vehicles, ships, or aircraft. This application provides an electrical device that uses a battery as a power source. This device can be, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0053] For ease of explanation, the following embodiments use a vehicle as an example of an electrical device according to an embodiment of this application.

[0054] See Figure 1 , Figure 1 This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. The vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is disposed inside the vehicle 1000, and the battery 100 can be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power needs of the vehicle 1000 during startup, navigation, and driving.

[0055] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0056] In this application, battery 100 refers to a single physical module comprising one or more battery cells 20 to provide a certain voltage and capacity, which may be in the form of a battery pack, battery module, etc. Battery 100 may include a housing 10 for encapsulating one or more battery cells 20, the housing 10 preventing liquids or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0057] See Figure 2 , Figure 2This is an exploded view of a battery 100 provided in some embodiments of this application. The battery 100 includes a housing 10 and a plurality of battery cells 20, which are housed within the housing 10. The housing 10 is used to house the battery cells 20 and can have various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, defining a receiving space 13 for accommodating the battery cells 20. The second portion 12 may be a hollow structure with one open end, and the first portion 11 may be a plate-like structure, overlapping the open side of the second portion 12 to form a housing 10 with the receiving space 13; alternatively, the first portion 11 and the second portion 12 may both be hollow structures with one open side, overlapping the open side of the second portion 12 to form a housing 10 with the receiving space 13. Of course, the first portion 11 and the second portion 12 can have various shapes, such as cylinders, cuboids, etc.

[0058] In battery 100, multiple battery cells 20 can be connected in series, parallel, or in a mixed configuration. A mixed configuration means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed configuration, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed configuration to form modules, and then these modules can be connected in series, parallel, or in a mixed configuration to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, multiple battery cells 20 can be electrically connected through a busbar component to achieve parallel, series, or mixed configurations of the multiple battery cells 20.

[0059] The battery cell 20 refers to the smallest unit that makes up the battery pack. The battery cell 20 can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these.

[0060] See Figure 3 The battery cell 20 may include a housing 21, an electrode assembly 22 and an electrolyte, with the electrode assembly 22 and the electrolyte both housed within the housing 21.

[0061] The outer casing 21 may include a housing 211 and a cover 212. The housing 211 is an assembly that fits with the cover 212 to form an internal sealed space 213 of the battery cell 20, wherein the formed sealed space 213 can be used to accommodate the electrode assembly 22, electrolyte, and other components. The cover 212 is a component that covers the opening of the housing 211 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the cover 212 may be adapted to the shape of the housing 211 to fit the housing 211, and functional components such as electrode terminals 23 and pressure relief structures 24 may also be provided on the cover 212. A sealing ring may be provided between the opening of the housing 211 and the cover 212 to achieve a seal between the housing 211 and the cover 212.

[0062] The housing 211 and cover 212 can be of various shapes and sizes, such as cuboids, cylinders, and hexagonal prisms. Specifically, the shapes of the housing 211 and cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The materials of the housing 211 and cover 212 can be various, such as, but not limited to, metals like copper, iron, aluminum, stainless steel, and aluminum alloys. The materials of the sealing ring can be various, such as, but not limited to, materials resistant to electrolyte corrosion, high toughness, and fatigue resistance, such as PP (polypropylene), PC (polycarbonate), and PET (polyethylene terephthalate). A plating layer can be formed on the outer surface of the housing 211, and the plating layer material can be various, such as, but not limited to, corrosion-resistant materials like Ni and Cr.

[0063] The battery cell 20 can also be in a pouch form, such as a bag-type pouch. The material of the pouch can be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0064] Electrode assembly 22 includes a negative electrode, a separator, and a positive electrode 221 (see [reference]). Figure 4 and Figure 5 The battery cell 20 primarily functions by the movement of metal ions between the positive electrode 221 and the negative electrode. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrode 221. A separator is disposed between the positive and negative electrode 221, primarily to prevent short circuits between the positive and negative electrodes, while also allowing ions to pass through. The electrode assembly 22 can be a wound structure or a stacked structure; this embodiment is not limited to either.

[0065] The negative electrode sheet includes a negative current collector, a negative electrode tab, and a negative active material layer. The negative active material layer is disposed on at least one side of the negative current collector, and a base coating layer may also be disposed between the negative active material layer and the negative current collector. The negative electrode tab protrudes from the negative current collector and is located, for example, at one end of the negative current collector or at opposite ends.

[0066] The negative electrode current collector can be a metal foil or a composite current collector. For example, the materials of the negative electrode current collector and the negative electrode tab can be copper. The composite current collector can include a polymer material substrate and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] The negative electrode active material in the negative electrode active material layer can be carbon, silicon, or other negative electrode active material materials. As an example, the negative electrode active material material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active material materials may also be used.

[0068] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0069] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0071] The separator is located between the positive electrode 221 and the negative electrode, and plays a role in isolation. In this embodiment, there is no particular limitation on the type of separator, and any well-known porous structure separator with good chemical and mechanical stability can be selected.

[0072] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0073] See Figure 4 and Figure 5 The positive electrode 221 includes a positive current collector 2211 and a positive active material layer 2212. The positive active material layer 2212 is disposed on at least one side of the positive current collector 2211. An undercoating layer or the like may also be disposed between the positive active material layer 2212 and the positive current collector 2211.

[0074] The positive electrode current collector 2211 can be a metal foil or a composite current collector. For example, the material of the positive electrode current collector 2211 can be aluminum. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0075] Unless otherwise specified, the design requirements for the positive electrode active material layer 2212 can be carried out in accordance with the technical solutions proposed in the embodiments of this application.

[0076] In some embodiments, the positive electrode active material layer 2212 may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0077] In some embodiments, the positive electrode active material layer 2213 may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0078] The positive electrode 221 proposed in the embodiments of this application will be described in detail below.

[0079] See Figure 4In a first aspect, embodiments of this application provide a positive electrode 221, which includes a positive active material layer 2212. The positive active material layer 2212 includes a first positive active material layer 2212a and a second positive active material layer 2212b. The second positive active material layer 2212b is located outside the first positive active material layer 2212a and includes a second positive active material. The thickness of the first positive active material accounts for H (in %) of the total thickness of the positive active material layer 2212, and the lattice volume shrinkage rate of the second positive active material layer 2212b is V (in %). The relationship between V and H satisfies: .

[0080] The second positive electrode active material layer 2212b is located outside the first positive electrode active material layer 2212a, meaning that the second positive electrode active material layer 2212b is located on the side of the first positive electrode active material layer 2212a away from the positive electrode current collector 2211. In the embodiments of this application, the descriptions of the active material layer being located inside and outside refer to their relative positions within the electrode sheet; that is, in the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b, the inner active material layer refers to the first positive electrode active material layer 2212a, and the outer active material layer refers to the first positive electrode active material layer 2212a. The first positive electrode active material layer 2212a includes a first positive electrode active material. For example, the first positive electrode active material and the second positive electrode active material are of different types.

[0081] In both the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b, an adhesive and / or a conductive agent are exemplaryly included; the amount and / or type of the adhesive may be the same or different, and the amount and / or type of the conductive agent may be the same or different.

[0082] Among the parameters related to parameter H, the thickness value corresponding to each structure refers to its dimension in the thickness direction A of the positive electrode sheet. This can be tested using conventional methods, such as scanning electron microscopy. Taking the positive electrode active material layer 2212, which consists of a first positive electrode active material layer 2212a and a second positive electrode active material layer 2212b, as an example, refer to... Figure 1 The total thickness of the positive electrode active material layer 2212 is denoted by h_total, the thickness of the first positive electrode active material layer 2212a is denoted by h1, and the thickness of the second positive electrode active material layer 2212b is denoted by h2. h_total = h1 + h2, and H = h1 / h_total.

[0083] Lattice volume shrinkage rate refers to the percentage reduction in the volume of a material's lattice under full-filled conditions compared to its fully-displaced conditions. Let v1 represent the lattice volume under full-displaced conditions and v2 represent the lattice volume under full-filled conditions, then V = (v1 - v2) / v1. The lattice volume can be measured using conventional methods, such as X-ray diffraction (XRD).

[0084] In the embodiments of this application, the value of V / H is, for example, but not limited to, any one of 3.3%, 6.6%, 7.7%, 8.5%, 10.0%, 14.3%, 20.0%, 24.0%, 28.6% or a range between any two.

[0085] In the technical solution of this application embodiment, the ratio between the lattice shrinkage rate of the outer positive electrode active material and the thickness ratio of the inner active material layer is adjusted to meet a certain range, so that the adjacent active material layers have a better matching charge and discharge capability, which is beneficial to improving cycle stability.

[0086] In some embodiments, V and H satisfy the following relationship: .

[0087] In these embodiments, the ratio of V value to H value meets a further range, so that adjacent active material layers have a more matched charge and discharge capability, which is beneficial to improve cycle stability.

[0088] In some embodiments, the value of V satisfies: 2% ≤ V ≤ 4%; alternatively, the value of V satisfies: 2% ≤ V ≤ 3%.

[0089] As an example, the value of V can be, for example, but not limited to, any point value of 2%, 2.5%, 3%, 3.5%, 4%, or a range of any two.

[0090] It should be noted that in other embodiments of this application, the value of V may also be 1%~4%, 1%~5%, 1%~6%, 2%~5%, or 2%~6%.

[0091] In these embodiments, the second positive electrode active material has a small lattice shrinkage rate, which is beneficial for improving the phenomenon of cracking and breakage of the second positive electrode active material; at the same time, it is beneficial for controlling the ratio of V value to H value within a suitable range, which can improve cycle stability. In addition, under the condition of satisfying this V value, there are more ternary positive electrode materials (such as nickel-cobalt-manganese ternary materials) to choose from, which is beneficial for improving energy density.

[0092] In some embodiments, the value of H satisfies: 14% ≤ H ≤ 61%; alternatively, the value of H satisfies: 14% ≤ H ≤ 39%.

[0093] As an example, the value of H can be, for example, but not limited to, any point value of 14%, 19%, 29%, 39%, 49%, 61%, or a range of any two.

[0094] It should be noted that in other embodiments of this application, the value of H can also be 10%~61%, 10%~64%, 10%~71%, 12%~61%, 12%~64%, or 12%~71%.

[0095] In these embodiments, the thickness ratio of the inner active material layer meets a certain range. When the ratio requirement of V value and H value is met, the V value can meet a suitable range, which is beneficial to improving cycle stability. At the same time, it is beneficial to better match the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b and perform their respective functions. When the first positive electrode active material in the first positive electrode active material layer 2212a includes a highly stable lithium phosphate, the thickness ratio of the first positive electrode active material layer 2212a is above a certain standard, which also makes the first positive electrode active material layer 2212a have a certain charge and discharge capability, which is beneficial to improving cycle stability.

[0096] In some embodiments, the first positive electrode active material layer 2212a includes a first positive electrode active material, and the specific surface area BET of the first positive electrode active material satisfies: 7 m² / g. 2 / g≤BET≤24m 2 / g; Optionally, BET satisfies: 9m 2 / g≤BET≤22m 2 / g.

[0097] Specific surface area can be tested using conventional methods, such as weighing a certain mass of the first positive electrode active material and then detecting it using a specific surface area and porosity analyzer.

[0098] As an example, the specific surface area BET of the first positive electrode active material may be, for example, but not limited to, 7m². 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 Any point value in / g or any range of values ​​between the two.

[0099] In these embodiments, the specific surface area (BET) of the first positive electrode active material is above a certain standard, giving it good electrochemical activity; the specific surface area (BET) of the first positive electrode active material is below a certain standard, which can improve the deterioration of cycle stability caused by water absorption of the material.

[0100] In some embodiments, the first positive electrode active material layer 2212a includes a first positive electrode active material, which includes a doped or undoped lithium phosphate; and / or the second positive electrode active material includes a ternary positive electrode material.

[0101] Lithium phosphates may or may not contain doping elements, such as, but not limited to, materials composed of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese iron phosphate, and doping elements.

[0102] Ternary cathode materials include NCM (nickel-cobalt-manganese) materials and NCA (nickel-cobalt-aluminum) materials.

[0103] In these embodiments, lithium phosphate has good stability, and ternary cathode materials have high energy density, which is beneficial for balancing good cycle stability and energy density.

[0104] In some embodiments, lithium phosphates include Li 1+x Mn 1-y A y P 1-z E z O4, -0.100≤x≤0.100, 0.001≤y≤0.500, 0.001≤z≤0.100, element A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb or Ge, and element E includes one or more of B, Si, N, S, F, Cl or Br.

[0105] Optionally, element A includes one or more of Fe, Ti, V, Ni, Co, or Mg.

[0106] Optionally, element E includes one of B, Si, N, and S.

[0107] In these embodiments, lithium phosphates exhibit good electrochemical performance, such as good stability.

[0108] In some embodiments, the ternary cathode material includes Li a Nib Co c M1 d M2 e O f R g , 0.75 ≤ a ≤ 1.2, 0.4 < b < 0.7, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3. Element M1 includes Mn and / or Al. Element M2 includes one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb. Element R includes one or more of N, F, S or Cl.

[0109] In the embodiments of the present application, the chemical formula of the lithium-containing phosphate and the ternary cathode material can be tested by conventional methods, such as measuring the element composition by ICP (Inductively Coupled Plasma Emission Spectrometer).

[0110] In these embodiments, the ternary cathode material has good electrochemical properties, such as high energy density, appropriate lattice shrinkage rate, etc.

[0111] In some embodiments, the lithium-containing phosphate includes Fe element, and the ternary cathode material includes Mn element; in the positive electrode active material layer 2212, the mass ratio of Fe element to Mn element is 0.03 - 0.25.

[0112] Optionally, the lithium-containing phosphate is a material composed of lithium iron manganese phosphate and doping elements; the ternary cathode material is a nickel cobalt manganese ternary material and does not contain Fe element.

[0113] As an example, the mass ratio of Fe element to Mn element is, for example but not limited to, any one of the point values 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25 or the range value between any two of them.

[0114] It should be noted that in other embodiments of the present application, the mass ratio of Fe element to Mn element can also be 0.02 - 0.25, 0.02 - 0.26, 0.02 - 0.27, 0.02 - 0.28, 0.03 - 0.26, 0.03 - 0.27 or 0.03 - 0.28.

[0115] The mass ratio of Fe to Mn can be tested using conventional methods. For example, the positive electrode 221 can be placed in a treatment solution such as acid to digest the positive electrode active material layer 2212. Then, the mass fraction of Fe and Mn can be measured by ICP, and the mass ratio of Fe to Mn can be calculated based on this.

[0116] In these embodiments, the mass ratio of Fe to Mn elements meets a certain range, which is beneficial to control the H value within a suitable range, thereby improving the cycle stability.

[0117] In some embodiments, the mass ratio of Fe to Mn elements in the positive electrode active material layer 2212 is 0.05 to 0.20.

[0118] In these embodiments, the mass ratio of Fe to Mn elements is within a further range, which is beneficial for controlling the H value within a more suitable range, thereby improving cycle stability.

[0119] In some embodiments, the positive electrode active material further includes at least one coating layer covering at least a portion of the surface of the first positive electrode active material and / or the second positive electrode active material. The coating layer includes one or more of oxides, nitrates, phosphates, or carbonates containing a specified element. The specified element includes one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, or P. The coating layer includes one or more of pyrophosphates, phosphates, or carbon.

[0120] As an example, the coating layer covering at least a portion of the surface of the first positive electrode active material is a first coating layer, which, for example, covers at least a portion of the surface of a lithium phosphate-containing material. The first coating layer comprises one or more of an oxide, nitrate, phosphate, or carbonate containing a specified element.

[0121] As an example, the coating layer covering at least a portion of the surface of the second positive electrode active material is called the second coating layer, which, for example, covers at least a portion of the surface of the ternary positive electrode material. The second coating layer comprises one or more of pyrophosphate, phosphate, or carbon.

[0122] Optionally, the second coating layer includes one or more of Al2O3, B2O3, or TiO2.

[0123] The first coating layer can completely or partially coat the lithium phosphate, and can be one or more layers. In the case of multiple layers, the materials of different layers can be the same or different. Similarly, the second coating layer can completely or partially coat the ternary cathode material, and can be one or more layers. In the case of multiple layers, the materials of different layers can be the same or different.

[0124] In these embodiments, the coating layer can modify the positive electrode active material.

[0125] See Figure 5 In some embodiments, the positive electrode 221 further includes a hydrophobic conductive layer 2213, which is located between the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b, and the hydrophobic conductive layer 2213 includes a hydrophobic conductive material.

[0126] Hydrophobic conductive materials can include materials that are both hydrophobic and conductive, or they can be a combination of hydrophobic and conductive materials.

[0127] Optionally, the water contact angle of the hydrophobic conductive material is >130°.

[0128] In addition to hydrophobic conductive materials, the hydrophobic conductive layer 2213 may also include adhesives, etc.

[0129] It should be noted that the hydrophobic conductive layer 2213 is only located between the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b, but it does not belong to the positive electrode active material layer 2212. That is to say, when calculating the H value, the thickness of the hydrophobic conductive layer 2213 is not included in the total thickness h of the positive electrode active material layer 2212.

[0130] In these embodiments, the hydrophobic conductive layer 2213 has both hydrophobic and conductive functions. The conductive function enables the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b to maintain good conductivity, while the hydrophobic function helps to improve cycle stability.

[0131] In some embodiments, the hydrophobic conductive material includes a hydrophobic conductive polymer and a hydrophobic conductive carbon.

[0132] In these embodiments, the combination of hydrophobic conductive polymer and hydrophobic conductive carbon can provide good conductivity and hydrophobicity.

[0133] In some embodiments, the hydrophobic conductive polymer includes one or more of polypyrrole, polyaniline, polythiophene, or polyacetylene; and / or the hydrophobic conductive carbon includes one or more of hydrophobic carbon nanotubes or hydrophobic carbon nanofibers.

[0134] Optionally, the hydrophobic conductive polymer includes polythiophene and / or polyaniline; as an example, the hydrophobic conductive polymer is polyaniline.

[0135] In these embodiments, the hydrophobic conductive polymer and the hydrophobic conductive carbon are suitable choices that can well meet the performance requirements for hydrophobic conductive materials.

[0136] In some embodiments, the mass percentage of hydrophobic conductive carbon in the hydrophobic conductive material is 2% to 10%.

[0137] As an example, the mass percentage of hydrophobic conductive carbon is, for example, but not limited to, any one of 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range between any two.

[0138] In these embodiments, the hydrophobic conductive carbon has a suitable mass ratio in the hydrophobic conductive material, which enables the performance requirements of the hydrophobic conductive material to be well met.

[0139] Secondly, embodiments of this application provide a battery 100, including the positive electrode 221 described in the above embodiments.

[0140] Thirdly, embodiments of this application provide an electrical device including the battery 100 described in the above embodiments.

[0141] The following specific embodiments are provided to better illustrate this application.

[0142] I. Preparation of battery cells Preparation of the positive electrode sheet Preparation of the first positive electrode active material layer: The first positive electrode active material, lithium manganese iron phosphate, is composed of a material (chemical formula LiMn) and doping elements. 0.6 Fe 0.4 P 0.995 S 0.005 O4), conductive carbon, and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a mass ratio of 90:5:5. The mixture is stirred and mixed evenly to obtain a first coating slurry with a viscosity controlled at 3000 mPa·S ~ 10000 mPa·S. The first coating slurry is coated on an aluminum foil and dried to form a first positive electrode active material layer on the positive electrode current collector.

[0143] Preparation of the second positive electrode active material layer: The positive electrode active material is replaced with the same mass of NCM (chemical formula LiNi). 0.55 Co 0.05 Mn 0.4 The second coating slurry is obtained by coating the first positive electrode active material layer with the second coating slurry and drying it to form the second positive electrode active material layer on the first positive electrode active material layer.

[0144] The positive electrode sheet is obtained through rolling and die cutting.

[0145] in: In an embodiment containing a hydrophobic conductive layer, a hydrophobic conductive layer is first formed on the first positive electrode active material layer before the second positive electrode active material layer is prepared, and then the second positive electrode active material layer is formed on the hydrophobic conductive layer.

[0146] Preparation of hydrophobic conductive layer: A hydrophobic conductive material is composed of polyaniline and hydrophobic carbon nanotubes, with the proportion of hydrophobic carbon nanotubes in the hydrophobic conductive material being 4wt%; the hydrophobic conductive material is prepared into a slurry and then coated on the first positive electrode active material layer to form a hydrophobic conductive layer with a thickness of 8μm.

[0147] Preparation of the negative electrode sheet Graphite, sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and conductive carbon are added to a certain amount of deionized water. The mass ratio of graphite:sodium carboxymethyl cellulose:styrene-butadiene rubber:conductive agent is 90:2:3:5. The mixture is stirred to form a uniform negative electrode slurry with a viscosity controlled at 3000 Pa·S~10000 mPa·S. The negative electrode slurry is coated onto copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet is formed.

[0148] Preparation of Electrolyte It contains LiPF6 at a concentration of 1 mol / L in the electrolyte. The solvents include ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. It also contains fluoroethylene carbonate (FEC) at a concentration of 5 wt% in the electrolyte.

[0149] Preparation of the separating membrane Polyethylene (PE) porous polymer film is used as the separator.

[0150] [Preparation of Lithium-ion Batteries] The prepared positive electrode, negative electrode, and separator are stacked in a Z-shaped structure to form the corresponding battery cell. The battery cell is vacuum dried at 90°C for 12 hours, followed by ultrasonic welding of the positive and negative electrode tabs. The positive electrode uses aluminum tabs, and the negative electrode uses nickel tabs, with the positive and negative tabs located on the same side of the battery cell. The battery cell with welded tabs is then placed in an aluminum-plastic film of appropriate size for top-side sealing at a temperature of 145°C. Electrolyte is injected, and the cell is allowed to stand, form, age, vent, re-seal, and undergo capacity testing to obtain the prepared soft-pack stacked battery cell.

[0151] II. Testing Methods 1. Test of lattice volume shrinkage (V value) of the second positive electrode active material The battery cells prepared using the above experimental method were used as the test objects.

[0152] Fresh positive electrode sheets were inspected, and the a-axis and c-axis (material cell parameters) values ​​required for calculating the NCM material cell volume were obtained through XRD data and refinement using RietVeld software. Then, the NCM material lattice volume of the fresh positive electrode sheet was calculated using the formula v1 = a^2 × c × sin120°, which can be used to represent the NCM material lattice volume in the fully charged state, denoted as v1. Under a constant temperature environment of 25℃, at a voltage of 2.5V~4.4V, the material was charged to 4.4V using 0.5C0, and then... The battery was charged at a constant voltage of 4.4V until the current was ≤0.05C0. Then, the positive electrode was removed and XRD tests were performed. The a-axis and c-axis (material cell parameters) values ​​required to calculate the NCM material cell volume under full charge were obtained by refining the XRD data with RietVeld software. The NCM material lattice volume under full charge was then calculated using the formula v2=a^2×c×sin120°, denoted as v2. In the above calculation formula, a and c correspond to the a-axis and c-axis cell parameter values, respectively.

[0153] Calculate the lattice volume shrinkage rate: Lattice volume shrinkage rate = (v1-v2) / v1.

[0154] 2. Measurement of the proportion of the thickness of the first positive electrode active material layer to the total thickness of the positive electrode active material layer (H value). The positive electrode sheet was cut into 11mm×10mm pieces. The cut positive electrode sheet was immersed in a thermos containing liquid nitrogen for 10 minutes. The sample was removed with tweezers and quickly broken with a knife. The relatively flat cross-section was taken as the sample and placed on the sample stage. The cross-section was processed and tested using an IB-19500CP ion mill and a ZEISS SEM (Sigma 300) electron scanning microscope. The cross-sectional morphology was observed, and the thickness h1 of the first positive electrode active material layer and the total thickness htotal of the positive electrode active material layer were marked using the equipment.

[0155] Calculate the value of H, H = h1 / htotal.

[0156] 3. Specific surface area (BET) test of the first positive electrode active material The first positive electrode active material particles (LiMn) were removed from the first positive electrode active material layer using a scanning electron microscope. 0.6 Fe 0.4 P 0.995 S 0.005 O4) until the required sample amount of 8g is reached, then place it in a fully automated surface area and porosity analyzer (Tristar Ⅱ 3020) and test the material BET according to the test equipment program.

[0157] 4. Test of the mass ratio of Fe to Mn elements (Fe / Mn mass ratio) in the highly active material layer. Take 0.4g of the positive electrode sheet in a 25ml beaker, add 2ml~5ml of nitric acid, let it stand overnight, then place it on a hot plate and heat at about 100℃ (using a voltage regulator to adjust the input voltage and control the temperature) until the positive electrode sheet is digested. Add 0.5ml of perchloric acid and heat at about 140℃ to digest until the white fumes stop. The residue should be white. Otherwise, add nitric acid and perchloric acid again to repeat the digestion. Finally, dissolve and extract with 7% (volume percentage of acid) hydrochloric acid. Adjust the volume to an appropriate level according to the content of the element to be measured, and start testing the mass fraction of Mn and Fe on an ICP-OES inductively coupled plasma atomic emission spectrometer. The Mn / Fe mass ratio can then be calculated.

[0158] 5. Cyclic stability test The prepared pouch cells were charged to 4.4V at 0.5C0 under a constant temperature environment of 25℃ and a voltage range of 2.5V to 4.4V. Then, they were charged at 4.4V under constant voltage until the current was ≤0.05C0. After standing for 5 minutes, they were discharged to 2.5V at 1C0. The capacity was recorded as Cn (n=1,2,3...). The above operation was repeated. The capacity retention rate was calculated according to the ratio of Cn / C3. When Cn / C3×100%=80%, the corresponding number of cycles was extracted as the evaluation index of cycle capability.

[0159] III. Experimental Conditions and Test Results The main experimental conditions for each experimental group are shown in Table 1. For experimental conditions not recorded, please refer to the above records for details, which will not be repeated in this paper. The test results of cycle stability are also shown in Table 1.

[0160] Table 1. Main experimental conditions and cyclic stability test results

[0161] A brief analysis based on Table 1 above is as follows: In Examples 1 to 12, all conditions are met. In Comparative Examples 1 and 2, none of them satisfy the condition. Compared with Comparative Examples 1 to 2, the number of cycles when the cycle retention rate was 80% in Examples 1 to 12 was increased to varying degrees, indicating that the cycle stability was improved to varying degrees.

[0162] In Examples 1 to 5, Examples 2 to 4 further satisfy the following: Compared with other embodiments, Embodiments 2 to 4 showed better cycle counts when the cycle retention rate was 80%, indicating better cycle stability.

[0163] In Examples 1 to 7, Examples 1 to 5 also satisfy 2%≤V≤4% and 14%≤H≤61%, while Examples 6 and 7 do not satisfy 2%≤V≤4% and 14%≤H≤61%. Compared with Examples 6 and 7, the number of cycles when the cycle retention rate is 80% in Examples 1 to 5 has increased to varying degrees, indicating that the cycle stability has been improved to varying degrees.

[0164] In Examples 3, 8-11, the BET of the first positive electrode active material is different. Among them, Examples 3, 8, and 9 satisfy 9m. 2 / g≤BET≤22m 2 / g, compared with other examples, Examples 3, 8 and 9 have better cycle counts when the cycle retention rate is 80%, indicating better cycle stability.

[0165] Compared to Example 12, Example 12 also includes a hydrophobic conductive layer. Compared to Example 3, Example 12 has a better number of cycles with a cycle retention rate of 80%, indicating better cycle stability.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive active material layer, which includes a first positive active material layer and a second positive active material layer. The second positive active material layer is located outside the first positive active material layer and includes a second positive active material. The thickness of the first positive electrode active material layer accounts for H, which is a percentage of the total thickness of the positive electrode active material layer. The value of H satisfies: 14% ≤ H ≤ 61%; the lattice volume shrinkage rate of the second positive electrode active material is V, which is a percentage. The value of V satisfies: 2% ≤ V ≤ 4%.

2. The positive electrode sheet according to claim 1, characterized in that, The value of V satisfies: 2% ≤ V ≤ 3%.

3. The positive electrode sheet according to claim 1, characterized in that, The value of H satisfies: 14% ≤ H ≤ 39%.

4. The positive electrode sheet according to claim 1, characterized in that, The relationship between V and H satisfies: .

5. The positive electrode sheet according to claim 4, characterized in that, The following relationship is satisfied between V and H: .

6. The positive electrode sheet according to claim 1, characterized in that, The first positive electrode active material layer includes a first positive electrode active material, and the specific surface area (BET) of the first positive electrode active material satisfies: 7 m² 2 / g≤BET≤24m 2 / g.

7. The positive electrode sheet according to claim 6, characterized in that, The BET satisfies: 9m 2 / g≤BET≤22m 2 / g.

8. The positive electrode sheet according to claim 1, characterized in that, The first positive electrode active material layer includes a first positive electrode active material, which includes a lithium phosphate that is doped or undoped. and / or The second positive electrode active material includes ternary positive electrode materials.

9. The positive electrode sheet according to claim 8, characterized in that, The lithium-containing phosphate includes Li 1+x Mn 1-y A y P 1- z E z O4, -0.100≤x≤0.100, 0.001≤y≤0.500, 0.001≤z≤0.100, element A includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb or Ge, and element E includes one or more of B, Si, N, S, F, Cl or Br; and / or The ternary cathode material includes Li a Ni b Co c M1 d M2 e O f R g , 0.75 ≤ a ≤ 1.2, 0.4 < b < 0.7, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, 1 ≤ f ≤ 2.5, 0 ≤ g ≤ 1, f + g ≤ 3, the element M1 includes Mn and / or Al, the element M2 includes one or more of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W or Nb, and the element R includes one or more of N, F, S or Cl.

10. The positive electrode sheet according to claim 8 or 9, characterized in that, The lithium phosphate includes Fe, and the ternary cathode material includes Mn; in the cathode active material layer, the mass ratio of Fe to Mn is 0.03 to 0.

25.

11. The positive electrode sheet according to claim 10, characterized in that, In the positive electrode active material layer, the mass ratio of Fe to Mn elements is 0.05~0.

20.

12. The positive electrode sheet according to claim 8, characterized in that, The positive electrode active material further includes at least one coating layer covering at least a portion of the surface of the first positive electrode active material and / or the second positive electrode active material, wherein, The coating layer includes one or more of oxides, nitrates, phosphates, or carbonates containing a specified element, wherein the specified element includes one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B, or P; and / or The coating layer comprises one or more of pyrophosphate, phosphate, or carbon.

13. The positive electrode sheet according to claim 1, characterized in that, The positive electrode further includes a hydrophobic conductive layer, which is located between the first positive electrode active material layer and the second positive electrode active material layer, and the hydrophobic conductive layer includes a hydrophobic conductive material.

14. The positive electrode sheet according to claim 13, characterized in that, The hydrophobic conductive material includes hydrophobic conductive polymers and hydrophobic conductive carbon.

15. The positive electrode sheet according to claim 14, characterized in that, The hydrophobic conductive polymer includes one or more of polypyrrole, polyaniline, polythiophene, or polyacetylene. and / or The hydrophobic conductive carbon includes one or more of hydrophobic carbon nanotubes or hydrophobic carbon nanofibers.

16. The positive electrode sheet according to claim 14 or 15, characterized in that, In the hydrophobic conductive material, the mass percentage of the hydrophobic conductive carbon is 2% to 10%.

17. A battery, characterized in that, It includes the positive electrode sheet as described in any one of claims 1 to 16.

18. An electrical appliance, characterized in that, Includes the battery as described in claim 17.

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