Positive electrode sheet, battery, and electric device

Abstract

A positive electrode sheet, a battery and an electric device, wherein the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a first positive electrode active material layer and a second positive electrode active material layer, the second positive electrode active material layer is located on the outer side of the first positive electrode active material layer, and the second positive electrode active material layer comprises a second positive electrode active material; wherein the thickness ratio 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 %; the relationship between V and H satisfies: in the positive electrode sheet, the ratio between the lattice shrinkage rate of the positive electrode active material on the outer side and the thickness ratio of the active material layer on the inner side satisfies a certain range, so that the adjacent active material layers have relatively matched charge and discharge capacity, and the cycle stability is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a battery and an electric device. BACKGROUND

[0002] With the increasing requirements for energy density and stability, some technical solutions propose to use positive electrode active materials with different characteristics in a layered manner. However, the charge and discharge capacity matching between the active material layers arranged in layers is usually poor, which affects the cycle stability. SUMMARY

[0003] In view of the above problems, the present application provides a positive electrode sheet, a battery and an electric device, the charge and discharge capacity matching between the active material layers arranged in layers is good, which can improve the cycle stability.

[0004] Embodiments of the present application are implemented as follows:

[0005] In a first aspect, the embodiments of the present application provide a positive electrode sheet, which comprises a positive electrode active material layer, the positive electrode active material layer comprising a first positive electrode active material layer and a second positive electrode active material layer, the second positive electrode active material layer being located outside the first positive electrode active material layer, and the second positive electrode active material layer comprising a second positive electrode active material; wherein the thickness ratio of the first positive electrode active material layer in the total thickness of the positive electrode active material layer is H, in %; the lattice volume shrinkage rate of the second positive electrode active material is V, in %; and the relationship between V and H satisfies:

[0006] In the technical solution of the embodiments of the present application, the ratio between the lattice shrinkage rate of the positive electrode active material outside and the thickness ratio of the active material layer inside is controlled to satisfy a certain range, so that the adjacent active material layers have a better matching charge and discharge capacity, which is beneficial to improve the cycle stability.

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

[0008] In these embodiments, the ratio of the values of V and H satisfies a further range, so that the adjacent active material layers have a better matching charge and discharge capacity, which is beneficial to better improve the cycle stability.

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

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

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

[0012] In these embodiments, the thickness ratio of the inner active material layer satisfies a certain range, and when the ratio of V value and H value is met, the V value can satisfy a suitable range, which is beneficial to better improve the 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 play their respective functions; when the first positive electrode active material in the first positive electrode active material layer includes high-stability lithium-containing phosphates, the thickness ratio of the first positive electrode active material layer is above a certain standard, which also makes the first positive electrode active material layer have a certain charge and discharge capacity, and is beneficial to improve the 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: 7m 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, which makes itself have better 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 material water absorption on cycle stability.

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

[0016] In these embodiments, the lithium-containing phosphates have good stability, and the ternary positive electrode materials have high energy density, which is beneficial to balance good cycle stability and energy density.

[0017] In some embodiments, the lithium-containing 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 includes 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 includes one or more of B, Si, N, S, F, Cl or Br; and / or the ternary positive electrode 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, 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, and element R includes one or more of N, F, S or Cl.

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

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

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

[0021] In these embodiments, the mass ratio of the Fe element and the Mn element meets a certain range, which is conducive to regulating the H value in a suitable range, thereby being able to improve the cycle stability.

[0022] In some embodiments, the positive electrode active material further includes at least one coating layer coated on at least part 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 specified elements, and the specified elements include one or more of Al, Ba, Zn, Ti, Co, W, Y, Si, Sn, B or P; and / or the coating layer includes 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 tab further comprises a hydrophobic conductive layer, the hydrophobic conductive layer is located between the first positive electrode active material layer and the second positive electrode active material layer, and the hydrophobic conductive layer comprises 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 conductive performance, and the hydrophobic function is conducive to improving the cycle stability.

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

[0027] In these embodiments, the hydrophobic conductive polymer and the hydrophobic conductive carbon cooperate to provide good conductivity and hydrophobicity.

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

[0029] In these embodiments, the hydrophobic conductive polymer and the hydrophobic conductive carbon have a suitable selection, which can better meet the performance requirements of the hydrophobic conductive material.

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

[0031] In these embodiments, the hydrophobic conductive carbon has a suitable mass percentage in the hydrophobic conductive material, which can better meet the performance requirements of the hydrophobic conductive material.

[0032] In a second aspect, the embodiments of the present application provide a battery comprising the positive electrode tab of the above embodiments.

[0033] In a third aspect, the embodiments of the present application provide an electrical device comprising the battery of the above embodiments.

[0034] The above description is only a summary of the technical solutions of the embodiments of the present application. In order to more clearly understand the technical means of the present application, the embodiments can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0036] Figure 1 A structural schematic diagram of a vehicle provided for some embodiments of the present application;

[0037] Figure 2 An exploded view of a battery provided for some embodiments of the present application;

[0038] Figure 3 An exploded view of a battery cell provided for some embodiments of the present application;

[0039] Figure 4 A structural schematic diagram of a first positive electrode tab provided for some embodiments of the present application;

[0040] Figure 5 A structural schematic diagram of a second positive electrode tab provided for some embodiments of the present application.

[0041] Icon:

[0042] 1000-vehicle;

[0043] 100-battery; 200-controller; 300-motor;

[0044] 10-box; 11-first part; 12-second part; 13-accommodation space;

[0045] 20-battery cell; 21-housing; 22-electrode assembly; 23-electrode terminal; 24-pressure relief structure;

[0046] 211-housing; 212-cover; 213-sealed space;

[0047] 221-positive electrode tab; 2211-positive electrode current collector; 2212-positive electrode active material layer; 2212a-first positive electrode active material layer; 2212b-second positive electrode active material layer; 2213-hydrophobic conductive layer;

[0048] A-thickness direction of the positive electrode tab. DETAILED DESCRIPTION

[0049] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. The specific conditions not noted in the embodiments are carried out according to the conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments not noted by the manufacturers are all conventional products which can be obtained by the market purchase.

[0050] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to make the technical solutions of the present application clearer, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0051] 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 belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application; the terms "comprising" and "having", and any variations thereof, as used in the specification and claims and the aforementioned description of the drawings, are intended to cover not exclusive inclusion.

[0052] In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0053] In the description of the embodiments of the present application, the technical term "and / or", such as "feature 1 and / or feature 2", means that it can be "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2". In addition, the character " / " in this paper generally indicates that the front and rear associated objects are in an "or" relationship.

[0054] In the description of the embodiments of the present application, unless otherwise specified, the meaning of "multiple" in "one or more" is two and more than two.

[0055] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification indicates that the described features, structures, or characteristics are not necessarily included in all embodiments, are not mutually exclusive alternatives to one another, and are not necessarily independent of one another. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0056] In the embodiments of the present application, the same reference signs represent 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 the present application shown in the drawings, and the overall height, length, width, and other dimensions of the integrated device are only exemplary and should not constitute any limitation on the present application.

[0057] From the development of market situation, the application of power battery is more and more extensive. The power battery is not only applied to the energy storage power supply system of hydroelectric, thermal, wind and solar power stations, but also widely applied to electric bicycles, electric motorcycles, electric vehicles and other electric vehicles, military equipment, aerospace and other fields. With the continuous expansion of the application field of power battery, the market demand is also increasing.

[0058] In the electrode tab manufacturing process of lithium ion secondary battery, single-layer coating is usually used, and the required active material is coated on the current collector in a single layer. With the increasing requirements for energy density and stability, some technical solutions propose to use positive active materials with different characteristics in layers, for example, to use positive active materials with high energy density characteristics (such as ternary system materials) and positive active materials with high stability characteristics (such as lithium-containing phosphates) in layers to balance energy density and stability.

[0059] During the cycle process, the active material on the outer side of the positive active material layer is more easily deintercalated lithium because it is closer to the negative electrode tab. The actual deintercalation lithium degree caused by charging and discharging is greater than the apparent deintercalation lithium degree (for example, the apparent charging and discharging voltage interval is 2.5V-4.4V, and the actual charging and discharging voltage interval is 2.45V-4.45V). A wider charging and discharging interval will bring greater volume change to the active material, and greater volume change will easily lead to cracks and breakage of the active material, thereby affecting the cycle stability.

[0060] The lattice shrinkage rate can control the volume change. The material with smaller lattice shrinkage rate has smaller volume change, which can improve the cracking and breaking phenomenon of the active material on the outer side. However, the material with smaller lattice shrinkage rate has poor rate performance, is not easy to be compatible with the adjacent active material layer, and also affects the cycle stability.

[0061] For the technical solution of coating multiple active material layers, although the mechanism is not very clear, the inventors of the present application found that: under the condition that the material type of the active material is certain, when the rate performance of the active material decreases, the active material layer needs to have a larger proportion in the multiple active material layers to match the charge and discharge capacity of the adjacent active material layer, so that the active material layers have better matching, which is beneficial to improve the cycle stability. That is to say, under the condition that the type of the active material inside and outside is certain, when the lattice shrinkage rate of the active material outside increases, the rate performance of the active material outside improves, and the thickness proportion of the active material layer outside needs to be reduced, and the thickness proportion of the active material layer inside needs to be increased correspondingly; conversely, the same reasoning applies.

[0062] Based on this, the present application provides a positive electrode sheet, which regulates the ratio between the lattice shrinkage rate of the active material outside and the thickness proportion of the active material layer inside to meet a certain range, that is, when the lattice shrinkage rate of the active material outside increases, the active material layer inside has a relatively larger thickness proportion correspondingly, and when the lattice shrinkage rate of the active material outside decreases, the active material layer inside has a relatively smaller thickness proportion correspondingly, so that the adjacent active material layers have a relatively matched charge and discharge capacity, which is beneficial to improve the cycle stability.

[0063] The battery cell using the positive electrode sheet disclosed in the embodiments of the present application can be used in, but is not limited to, an electric device for a vehicle, a ship or an aircraft. The embodiments of the present application provide an electric device using a battery as a power source, which can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric automobile, a ship, a spacecraft, etc. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric automobile toy, an electric ship toy and an electric aircraft toy, etc. The spacecraft can include an airplane, a rocket, a space shuttle and a spacecraft, etc.

[0064] The following embodiments are described for convenience with a vehicle as an example of an electric device according to the embodiments of the present application.

[0065] Referring to Figure 1 , Figure 1A structural schematic diagram of a vehicle 1000 is provided for some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle, or a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle, or a range extended vehicle, etc. The vehicle 1000 is internally provided with a battery 100, which can be arranged at the bottom, head, or tail of the vehicle 1000. The battery 100 can be used for power supply of the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further 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 demand of the vehicle 1000 during starting, navigation, and driving.

[0066] In some embodiments of the present application, the battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0067] In the present application, the battery 100 refers to a single physical module including one or more battery monomers 20 to provide a certain voltage and capacity, which can be in the form of a battery pack, a battery module, etc. The battery 100 can include a box 10 for packaging one or more battery monomers 20, and the box 10 can avoid the influence of liquid or other foreign matters on the charging or discharging of the battery monomer 20.

[0068] Referring to Figure 2 , Figure 2 An exploded view of the battery 100 is provided for some embodiments of the present application. The battery 100 includes a box 10 and a plurality of battery monomers 20, and the plurality of battery monomers 20 are contained in the box 10. Among them, the box 10 is used to contain the battery monomer 20, and the box 10 can be of various structures. In some embodiments, the box 10 can include a first part 11 and a second part 12, the first part 11 and the second part 12 are mutually covered, and the first part 11 and the second part 12 jointly define a containing space 13 for containing the battery monomer 20. The second part 12 can be a hollow structure with one end open, and the first part 11 is a plate-shaped structure, which is covered on the open side of the second part 12 to form the box 10 with the containing space 13; the first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 is covered on the open side of the second part 12 to form the box 10 with the containing space 13. Of course, the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0069] In the battery 100, a plurality of battery cells 20 can be connected in series, in parallel, or in a mixed manner, where the mixed manner refers to a manner in which a plurality of battery cells 20 are connected in series and in parallel. The plurality of battery cells 20 can be directly connected in series, in parallel, or in a mixed manner, and the plurality of battery cells 20 can be accommodated in the case 10 as a whole. Alternatively, the plurality of battery cells 20 can be connected in series, in parallel, or in a mixed manner to form a module, and a plurality of modules can be connected in series, in parallel, or in a mixed manner to form a whole and can be accommodated in the case 10. The battery 100 can include other structures, for example, a plurality of battery cells 20 can be electrically connected by a busbar to be connected in parallel, in series, or in a mixed manner.

[0070] The battery cell 20 refers to the smallest unit constituting a 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 thereto.

[0071] Referring to FIG. 1, Figure 3 The battery cell 20 can include a case 21, an electrode assembly 22, and an electrolyte, and the electrode assembly 22 and the electrolyte can be accommodated in the case 21.

[0072] The case 21 can include a case body 211 and a cover 212. The case body 211 is a component for fitting the cover 212 to form an internal sealed space 213 of the battery cell 20, and the formed sealed space 213 can be used to accommodate the electrode assembly 22, the electrolyte, and other components. The cover 212 refers to a component that is fitted to an opening of the case body 211 to isolate the internal environment of the battery cell 20 from the external environment, and the shape of the cover 212 can be adapted to the shape of the case body 211 to fit the case body 211. The cover 212 can further include functional components such as an electrode terminal 23, a pressure relief structure 24, etc. A sealing ring can be disposed between the opening of the case body 211 and the cover 212 to seal the case body 211 and the cover 212.

[0073] The case body 211 and the cover 212 can have various shapes and sizes, such as a rectangular parallelepiped shape, a cylindrical shape, a hexagonal prism shape, etc. Specifically, the shape of the case body 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The case body 211 and the cover 212 can be made of various materials, such as, but not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, etc. The sealing ring can be made of various materials, such as, but not limited to, PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate), etc. The outer surface of the case body 211 can be plated, and the plating layer can be made of various materials, such as, but not limited to, Ni, Cr, etc.

[0074] The battery cell 20 can also be in a soft package form, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, and the like can be listed.

[0075] The electrode assembly 22 includes a negative electrode sheet, a separator, and a positive electrode sheet 221 (see Figure 4 and Figure 5 ). The battery cell 20 mainly works by moving metal ions between the positive electrode sheet 221 and the negative electrode sheet. During charging and discharging, active ions are repeatedly intercalated and deintercalated between the positive electrode sheet 221 and the negative electrode sheet; the separator is disposed between the positive electrode sheet 221 and the negative electrode sheet, mainly to prevent short circuiting between the positive and negative electrodes, while allowing ions to pass through. The electrode assembly 22 can be in a jelly-roll structure or a stacked structure, and the embodiments of the present application are not limited thereto.

[0076] The negative electrode sheet includes a negative electrode current collector, a negative electrode tab, and a negative electrode active material layer, the negative electrode active material layer is disposed on at least one side of the negative electrode current collector, and a primer layer or the like can also be disposed between the negative electrode active material layer and the negative electrode current collector; the negative electrode tab protrudes from the negative electrode current collector, and the negative electrode tab is located at one end or opposite ends of the negative electrode current collector, for example.

[0077] The negative electrode current collector can be a metal foil or a composite current collector, for example, the material of the negative electrode current collector and the negative electrode tab can be copper, and the composite current collector can include a high polymer material base layer and a metal layer formed on at least one side of the high polymer material base layer, and 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 high polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0078] The negative electrode active material in the negative electrode active material layer can be a carbon, silicon, or the like. As an example, the negative electrode active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials can also be used.

[0079] In some embodiments, the negative active material layer can also optionally include a binder. The binder can 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).

[0080] In some embodiments, the negative active material layer can also optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0081] In some embodiments, the negative active material layer can also optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0082] The separator film is between the positive electrode tab 221 and the negative electrode tab, and serves the function of separation; the type of the separator film is not particularly limited in the embodiments of the present application, and any known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0083] In some embodiments, the material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0084] Referring to Figure 4 and Figure 5 , the positive electrode tab 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, and a primer layer or the like can also be disposed between the positive active material layer 2212 and the positive current collector 2211.

[0085] The positive current collector 2211 can be a metal foil or a composite current collector, for example, the material of the positive current collector 2211 can be aluminum. The composite current collector can include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer, and 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 base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0086] The design requirements of the positive active material layer 2212 can be designed according to the technical solutions proposed in the embodiments of the present application, except for special instructions.

[0087] In some embodiments, the positive electrode active material layer 2212 optionally further includes a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylic ester resin.

[0088] In some embodiments, the positive electrode active material layer 2213 optionally further includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] Next, the positive electrode tab 221 proposed by the embodiments of the present application is described in detail.

[0090] Referring to Figure 4 , in a first aspect, the embodiments of the present application provide a positive electrode tab 221, the positive electrode tab 221 includes a positive electrode active material layer 2212, the positive electrode active material layer 2212 includes a first positive electrode active material layer 2212a and a second positive electrode active material layer 2212b, the second positive electrode active material layer 2212b is located on the outer side of the first positive electrode active material layer 2212a, and the second positive electrode active material layer 2212b includes a second positive electrode active material; wherein the thickness ratio of the first positive electrode active material in the total thickness of the positive electrode active material layer 2212 is H, the unit is %; the lattice volume shrinkage rate of the second positive electrode active material layer 2212b is V, the unit is %; the relationship between V and H satisfies:

[0091] The second positive electrode active material layer 2212b is located on the outer side of the first positive electrode active material layer 2212a, which means 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 the present application, the description of the active material layer on the inner side and the outer side is relative to its position in the tab; that is, in the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b, the active material layer on the inner side refers to the first positive electrode active material layer 2212a, and the active material layer on the outer side refers to the first positive electrode active material layer 2212a

[0092] The first positive electrode active material layer 2212a includes a first positive electrode active material, and exemplarily, the first positive electrode active material and the second positive electrode active material are different in kind.

[0093] In the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b, the adhesives and / or the conductive agents are exemplarily included; the adhesives of the two can be the same or different in amount and / or type, and the conductive agents of the two can be the same or different in amount and / or type.

[0094] Among the parameters related to the value of H, the thickness value corresponding to each structure refers to its size in the thickness direction A of the positive electrode tab, which can be tested by a conventional method, for example, by a scanning electron microscope. Taking the positive electrode active material layer 2212 composed of the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b as an example, referring to Figure 1 , the total thickness of the positive electrode active material layer 2212 is denoted as htotal, the thickness of the first positive electrode active material layer 2212a is denoted as h1, the thickness of the second positive electrode active material layer 2212b is denoted as h2, htotal = h1 + h2, and H = h1 / htotal.

[0095] The lattice volume shrinkage rate refers to the percentage of the volume shrinkage of the material lattice in the full charge state relative to the full discharge state, and is denoted as v1 for the material lattice volume in the full discharge state and v2 for the material lattice volume in the full charge state, V = (v1-v2) / v1. Among them, the material lattice volume can be tested by a conventional method, for example, by X-ray diffraction (XRD) test.

[0096] In the embodiments of the present application, the value of V / H, for example but not limited to, is any one of 3.3%, 6.6%, 7.7%, 8.5%, 10.0%, 14.3%, 20.0%, 24.0%, 28.6% or a range value between any two of them.

[0097] In the technical solutions of the embodiments of the present application, the ratio between the lattice shrinkage rate of the positive electrode active material on the outer side and the thickness ratio of the active material layer on the inner side satisfies a certain range, so that the adjacent active material layers have a more matched charge and discharge capacity, which is beneficial to improve the cycle stability.

[0098] In some embodiments, V and H satisfy the following relationship:

[0099] In these embodiments, the ratio of the values of V and H satisfies a further range, so that the adjacent active material layers have a more matched charge and discharge capacity, which is beneficial to better improve the cycle stability.

[0100] In some embodiments, the value of V satisfies: 2%≤V≤4%; optionally, the value of V satisfies: 2%≤V≤3%.

[0101] As an example, the value of V is, for example but not limited to, any one of 2%, 2.5%, 3%, 3.5%, 4%, or a range value between any two of them.

[0102] It should be noted that in other embodiments of the present application, the value of V can also be 1%-4%, 1%-5%, 1%-6%, 2%-5%, or 2%-6%.

[0103] In these embodiments, the second positive electrode active material has a smaller lattice shrinkage rate, which is beneficial to improve the phenomenon of cracks and breakage of the second positive electrode active material; at the same time, it is beneficial to control the ratio of V value and H value in a suitable range, which can improve the cycle stability. In addition, under the condition of meeting the V value, there are more ternary positive electrode materials (such as nickel-cobalt-manganese ternary materials) to choose from, which is beneficial to improve the energy density.

[0104] In some embodiments, the value of H satisfies: 14%≤H≤61%; optionally, the value of H satisfies: 14%≤H≤39%.

[0105] As an example, the value of H is, for example but not limited to, any one of 14%, 19%, 29%, 39%, 49%, 61%, or a range value between any two of them.

[0106] It should be noted that in other embodiments of the present application, the value of H can also be 10%-61%, 10%-64%, 10%-71%, 12%-61%, 12%-64%, or 12%-71%.

[0107] In these embodiments, the thickness ratio of the inner active material layer satisfies a certain range, and when the ratio of V value and H value is satisfied, the V value can satisfy a suitable range, which is beneficial to better improve the 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 play their respective functions; when the first positive electrode active material in the first positive electrode active material layer 2212a includes high-stability lithium-containing phosphates, 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 capacity, which is beneficial to improve the cycle stability.

[0108] 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: 7m 2 / g≤BET≤24m 2 / g; optionally, BET satisfies: 9m 2 / g≤BET≤22m 2 / g.

[0109] The specific surface area can be tested by a conventional method, for example, a certain mass of the first positive electrode active material is taken and then detected by a specific surface area and porosity analyzer.

[0110] For example, the specific surface area BET of the first positive electrode active material is any one of 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, 17 m 2 / g, 18 m 2 / g, 19 m 2 / g, 20 m 2 / g, 21 m 2 / g, 22 m 2 / g, 23 m 2 / g, 24 m 2 / g, or a range value between any two of them.

[0111] In these embodiments, the specific surface area BET of the first positive electrode active material is above a certain standard, so that it has good electrochemical activity itself; the specific surface area BET of the first positive electrode active material is below a certain standard, which can improve the deterioration of the material water absorption on the cycle stability.

[0112] In some embodiments, the first positive electrode active material layer 2212a includes a first positive electrode active material, the first positive electrode active material includes a lithium-containing phosphatedoped or undoped; and / or the second positive electrode active material includes a ternary positive electrode material.

[0113] The lithium-containing phosphatedoped or undoped may, for example, but not limited to, include a material composed of lithium sodium iron phosphate, lithium manganese iron phosphate, lithium manganese iron phosphate and a doping element, etc.

[0114] The ternary positive electrode material may, for example, include an NCM (nickel-cobalt-manganese) system material, an NCA (nickel-cobalt-aluminum) system material, etc.

[0115] In these embodiments, the lithium-containing phosphatedopes has good stability, and the ternary positive electrode material has high energy density, which is beneficial to balance good cycle stability and energy density.

[0116] In some embodiments, the lithium-containing phosphatedopes include Li 1+x Mn 1-y Ay 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.

[0117] Optionally, element A includes one or more of Fe, Ti, V, Ni, Co or Mg.

[0118] Optionally, element E includes one or more of B, Si, N and S.

[0119] In these embodiments, the lithium-containing phosphate has good electrochemical performance, such as good stability.

[0120] In some embodiments, 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, 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, and element R includes one or more of N, F, S or Cl.

[0121] In embodiments of the present application, the chemical formula of the lithium-containing phosphate and the ternary cathode material can be tested using conventional methods, such as by ICP (inductively coupled plasma emission spectrometer) to measure the element composition.

[0122] In these embodiments, the ternary cathode material has good electrochemical performance, such as a high energy density, a suitable lattice shrinkage rate, etc.

[0123] In some embodiments, the lithium-containing phosphate includes an Fe element, and the ternary cathode material includes an Mn element; in the cathode active material layer 2212, the mass ratio of the Fe element to the Mn element is 0.03-0.25.

[0124] Optionally, the lithium-containing phosphate is a material composed of lithium manganese iron phosphate and a doping element; and the ternary cathode material is a nickel-cobalt-manganese ternary material, and does not contain an Fe element.

[0125] For example, the mass ratio of the Fe element and the Mn element is any one of the point values of 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 a range value between any two of them.

[0126] It should be noted that in other embodiments of the present application, the mass ratio of the Fe element and the 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.

[0127] The mass ratio of the Fe element and the Mn element can be tested by a conventional method, for example, the positive electrode sheet 221 is placed in an acid liquid or other treatment liquid to digest the positive electrode active material layer 2212, and then the mass fraction of the Fe element and the Mn element is measured by ICP, and the mass ratio of the Fe element and the Mn element is calculated based on this.

[0128] In these embodiments, the mass ratio of the Fe element and the Mn element meets a certain range, which is beneficial to regulate the H value in a suitable range, thereby better improving the cycle stability.

[0129] In some embodiments, in the positive electrode active material layer 2212, the mass ratio of the Fe element and the Mn element is 0.05-0.20.

[0130] In these embodiments, the mass ratio of the Fe element and the Mn element meets a further range, which is beneficial to regulate the H value in a more suitable range, thereby better improving the cycle stability.

[0131] In some embodiments, the positive electrode active material further includes at least one coating layer coated on at least part 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 specified elements, the specified elements include 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.

[0132] For example, the coating layer coated on at least part of the surface of the first positive electrode active material is a first coating layer, which is coated on at least part of the surface of the lithium-containing phosphate, for example. The first coating layer includes one or more of oxides, nitrates, phosphates, or carbonates containing specified elements.

[0133] As an example, the coating layer coated on at least part of the surface of the second positive electrode active material is a second coating layer, which is, for example, coated on at least part of the surface of the ternary positive electrode material. The second coating layer includes one or more of a pyrophosphate, a phosphate, or carbon.

[0134] Optionally, the second coating layer includes one or more of Al2O3, B2O3, or TiO2.

[0135] The first coating layer can fully coat or partially coat the lithium-containing phosphate, and can be one layer or multiple layers, and the materials in different layers can be the same or different. Similarly, the second coating layer can fully coat or partially coat the ternary positive electrode material, and can be one layer or multiple layers, and the materials in different layers can be the same or different.

[0136] In these embodiments, the coating layer can modify the positive electrode active material.

[0137] Referring to Figure 5 In some embodiments, the positive electrode tab 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.

[0138] The hydrophobic conductive material can be a material that has both hydrophobicity and conductivity, or can be a combination of a material with hydrophobicity and a material with conductivity.

[0139] Optionally, the water contact angle of the hydrophobic conductive material is > 130°.

[0140] In the hydrophobic conductive layer 2213, in addition to the hydrophobic conductive material, it can also include adhesives and the like.

[0141] 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 in position, but it does not belong to the positive electrode active material layer 2212. That is, in calculating the H value, the thickness of the hydrophobic conductive layer 2213 is not included in the total thickness htotal of the positive electrode active material layer 2212.

[0142] In these embodiments, the hydrophobic conductive layer 2213 has both hydrophobic and conductive functions. The conductive function allows the first positive electrode active material layer 2212a and the second positive electrode active material layer 2212b to maintain good conductivity, and the hydrophobic function is conducive to improving the cycle stability.

[0143] In some embodiments, the hydrophobic conductive material includes a hydrophobic conductive polymer and a hydrophobic conductive carbon.

[0144] In these embodiments, the hydrophobic conductive polymer and the hydrophobic conductive carbon are combined to provide good conductivity and hydrophobicity.

[0145] In some embodiments, the hydrophobic conductive polymer comprises one or more of polypyrrole, polyaniline, polythiophene, or polyacetylene; and / or the hydrophobic conductive carbon comprises one or more of hydrophobic carbon nanotubes or hydrophobic carbon nanofibers.

[0146] Optionally, the hydrophobic conductive polymer comprises polythiophene and / or polyaniline; as an example, the hydrophobic conductive polymer is polyaniline.

[0147] In these embodiments, the hydrophobic conductive polymer and the hydrophobic conductive carbon are suitably selected to meet the performance requirements of the hydrophobic conductive material.

[0148] In some embodiments, the mass percentage of the hydrophobic conductive carbon in the hydrophobic conductive material is 2% to 10%.

[0149] As an example, the mass percentage of the 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 value between any two of them.

[0150] In these embodiments, the hydrophobic conductive carbon has a suitable mass percentage in the hydrophobic conductive material, so that the performance requirements of the hydrophobic conductive material can be better met.

[0151] In a second aspect, the embodiments of the present application provide a battery 100 comprising the positive electrode sheet 221 of the above embodiments.

[0152] In a third aspect, the embodiments of the present application provide a power consumption device comprising the battery 100 of the above embodiments.

[0153] Some specific embodiments are listed below to better illustrate the present application.

[0154] I. Preparation of battery cell

[0155]

Preparation of positive electrode sheet

[0156] Preparation of first positive electrode active material layer: the material composed of the first positive electrode active material lithium manganese iron phosphate and the doping element (chemical formula LiMn 0.6 Fe 0.4 P 0.995 S 0.005O4), conductive carbon, and a binder polyvinylidene fluoride (PVDF) are added to N-methyl pyrrolidone (NMP) in a mass ratio of 90:5:5 to obtain a first coating layer slurry, and the viscosity is controlled to be 3000 mPa·S-10000 mPa·S; the first coating layer slurry is coated on an aluminum foil, and a first positive electrode active material layer is formed on the positive electrode current collector after drying.

[0157] Second positive electrode active material layer preparation: the positive electrode active material is replaced by the same mass of NCM (chemical formula LiNi 0.55 Co 0.05 Mn 0.4 ), to obtain a second coating layer slurry; the second coating layer slurry is coated on the first positive electrode active material layer, and a second positive electrode active material layer is formed on the first positive electrode active material layer after drying.

[0158] After rolling and die cutting, a positive electrode sheet is obtained.

[0159] Among them:

[0160] In the embodiment containing the hydrophobic conductive layer, before preparing the second positive electrode active material layer, a hydrophobic conductive layer is first formed on the first positive electrode active material layer, and then the second positive electrode active material layer is formed on the hydrophobic conductive layer.

[0161] Preparation of the hydrophobic conductive layer: polyaniline and hydrophobic carbon nanotubes are used to form a hydrophobic conductive material, and the proportion of hydrophobic carbon nanotubes in the hydrophobic conductive material is 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.

[0162]

Preparation of the negative electrode sheet

[0163] Graphite, sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and conductive carbon are added to a certain amount of deionized water, and the mass ratio of graphite: carboxymethyl cellulose: styrene butadiene rubber: conductive agent is 90:2:3:5, and the negative electrode slurry is stirred to be uniform, and the viscosity is controlled to be 3000Pa·S-10000 mPa·S; the above negative electrode slurry is coated on a copper foil, and after drying, cold pressing, and cutting processing, a negative electrode sheet is prepared.

[0164]

Preparation of the electrolyte

[0165] It contains LiPF6, and the concentration of LiPF6 in the electrolyte is 1mol / L. The solvent includes ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. It also contains fluoroethylene carbonate (FEC), and the content of FEC in the electrolyte is 5wt%.

[0166]

Preparation of the separator

[0167] The porous polymeric film is polyethylene (PE).

[0168]

Preparation of lithium ion battery

[0169] The prepared positive electrode sheet, negative electrode sheet and separator film are stacked in a Z-shaped structure to form a corresponding battery cell; the battery cell is vacuum dried at 90°C for 12h, and then the positive electrode tab and the negative electrode tab are ultrasonically welded, the positive electrode tab is an aluminum tab, the negative electrode tab is a nickel tab, and the positive electrode tab and the negative electrode tab are located on the same side of the battery cell; the battery cell after welding the tabs is packaged in an aluminum-plastic film of appropriate size for top-side sealing, the top-side sealing temperature is 145°C, electrolyte is injected, and then the battery cell is allowed to stand, formed, aged, degassed, resealed and tested for capacity to obtain the prepared soft-packaged stacked battery cell.

[0170] II. Test method

[0171] 1. Test of lattice volume shrinkage rate (V value) of second positive electrode active material

[0172] The battery cell prepared by the above experimental method is used as the detection object.

[0173] The fresh positive electrode sheet is detected, the a-axis and c-axis (material cell parameter) values required for calculating the NCM material cell volume are calculated by XRD data and RietVeld software refinement, then the NCM material lattice volume of the fresh positive electrode sheet is calculated by the formula v1=a^2×c×sin120°, which can be used to represent the NCM material lattice volume under full discharge state, denoted as v1; at 25°C constant temperature environment, 2.5V-4.4V, charge to 4.4V at 0.5C0, then charge to 4.4V at constant voltage until the current is less than or equal to 0.05C0, then disassemble the battery and take out the positive electrode sheet for XRD test; the a-axis and c-axis (material cell parameter) values required for calculating the NCM material cell volume under full charge state are obtained by XRD data and RietVeld software refinement, then the NCM material lattice volume under full charge state is calculated by the formula v2=a^2×c×sin120°, denoted as v2; in the above calculation formula, a and c respectively correspond to the a-axis and c-axis cell parameter values.

[0174] The lattice volume shrinkage rate is calculated, lattice volume shrinkage rate=(v1-v2) / v1.

[0175] 2. Test of ratio of thickness of first positive electrode active material layer to total thickness of positive electrode active material layer (H value)

[0176] The positive electrode sheet is cut into 11 mm x 10 mm, the cut positive electrode sheet is soaked in a thermos cup containing liquid nitrogen for 10 min, the sample is taken out with tweezers and quickly broken with a knife, a relatively flat cross section is taken as the sample and placed on a sample stage, and an IB-19500CP ion grinder and a ZEISS SEM (Sigma 300) electron scanning microscope are used for processing and testing, the cross section morphology is observed, and the thickness h1 of the first positive active material layer and the total thickness htotal of the positive active material layer are marked by using the equipment.

[0177] The H value is calculated, H = h1 / htotal.

[0178] 3. Specific surface area (BET) test of the first positive active material

[0179] The first positive active material particles (LiMn 0.6 Fe 0.4 P 0.995 S 0.005 O4) are taken from the first positive active material layer until the required sample amount of 8 g is reached, and the sample is placed in a full-automatic specific surface area and porosity analyzer (Tristar II 3020) to test the BET of the material according to the test equipment program.

[0180] 4. Test of the mass ratio of Fe element and Mn element (Fe / Mn mass ratio) in the positive active material layer

[0181] 0.4 g of the positive electrode sheet is taken in a 25 ml beaker, 2 ml to 5 ml of nitric acid is added, and it is placed overnight, then it is placed on an electric heating plate and heated at about 100°C (the input voltage is adjusted by a voltage regulator to control the temperature), until the positive electrode sheet is digested, then 0.5 ml of perchloric acid is added, and it is heated and digested at about 140°C until the white smoke disappears, the residue should be white, otherwise the nitric acid and perchloric acid should be added again for repeated digestion, finally it is dissolved and extracted with 7% (volume percentage of acid) hydrochloric acid, and the volume is adjusted to an appropriate volume according to the content of the element to be tested, then it is tested on an ICP-OES inductively coupled plasma emission spectrometer to start testing the mass fraction of Mn and Fe, and the Mn / Fe mass ratio can be calculated.

[0182] 5. Cycle stability test

[0183] The soft pack laminated battery prepared above is tested at 25°C constant temperature environment, 2.5V-4.4V, 0.5C0 charging to 4.4V, then constant voltage charging at 4.4V until the current is less than or equal to 0.05C0, standing for 5 min, then discharging at 1C0 to 2.5V, the capacity is recorded as Cn (n = 1, 2, 3…), the above operation is repeated, the capacity retention rate is calculated according to the ratio of Cn / C3, when Cn / C3 x 100% = 80%, the corresponding cycle number is extracted as the test index of cycle capacity.

[0184] III. Experimental conditions and test results

[0185] The main experimental conditions in each experimental group are shown in Table 1. For experimental conditions not described, refer to the above description, which will not be repeated here. The test results of the cycle stability are also shown in Table 1.

[0186] Table 1. Main experimental conditions and cycle stability test results

[0187]

[0188]

[0189] Brief analysis of the above Table 1 is as follows:

[0190] In Examples 1-12, all satisfy In Comparative Examples 1-2, all do not satisfy Compared with Comparative Examples 1-2, the cycle numbers of Examples 1-12 at a cycle retention rate of 80% are all improved to different degrees, indicating that the cycle stability is improved to different degrees.

[0191] In Examples 1-5, Examples 2-4 further satisfy Compared with other examples, the cycle numbers of Examples 2-4 at a cycle retention rate of 80% are better, indicating better cycle stability.

[0192] In Examples 1-7, Examples 1-5 also satisfy 2%≤V≤4% and 14%≤H≤61%, and Examples 6 and 7 do not satisfy 2%≤V≤4% and 14%≤H≤61%. Compared with Examples 6 and 7, the cycle numbers of Examples 1-5 at a cycle retention rate of 80% are all improved to different degrees, indicating that the cycle stability is improved to different degrees.

[0193] 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, and compared with other examples, the cycle numbers of Examples 3, 8 and 9 at a cycle retention rate of 80% are better, indicating better cycle stability.

[0194] Compared with Example 3, Example 12 further adds a hydrophobic conductive layer. Compared with Example 3, the cycle numbers of Example 12 at a cycle retention rate of 80% are better, indicating better cycle stability.

[0195] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be replaced equivalently. These modifications or replacements do not change the essence of the corresponding technical solutions, which should be covered in the scope of the present application. In particular, the technical features mentioned in each embodiment can be combined in any way as long as there is no structural conflict. The present 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 sheet, characterized by, The positive electrode tab comprises a positive electrode active material layer, the positive electrode active material layer comprises a first positive electrode active material layer and a second positive electrode active material layer, the second positive electrode active material layer is located outside the first positive electrode active material layer, and the second positive electrode active material layer comprises a second positive electrode active material; In the formula, H represents a ratio of a thickness of the first positive electrode active material layer to a total thickness of the positive electrode active material layer, and V represents a lattice volume shrinkage rate of the second positive electrode active material. The relationship between V and H satisfies the following formula: .

2. The cathode electrode of claim 1, wherein, the V and the H satisfy the following relationship: .

3. The positive electrode sheet according to claim 1 or 2, characterized by The value of V satisfies: 2%≤V≤4%.

4. The cathode electrode of claim 3, wherein, The value of V satisfies: 2%≤V≤3%.

5. The cathode sheet of claim 1, wherein, The value of H satisfies: 14%≤H≤61%.

6. The cathode electrode of claim 5, wherein, The value of H satisfies: 14%≤H≤39%.

7. The cathode electrode according to claim 1, wherein The first positive electrode active material layer includes a first positive electrode active material, a specific surface area BET of the first positive electrode active material satisfies: 7 m 2 / g ≤ BET ≤ 24 m 2 / g.

8. The cathode electrode of claim 7, wherein, The BET satisfies: 9 m 2 / g ≤ BET ≤ 22 m 2 / g.

9. The cathode electrode according to claim 1, wherein The first positive electrode active material layer comprises a first positive electrode active material, and the first positive electrode active material comprises a doped or undoped lithium-containing phosphate; And / or The second positive electrode active material comprises a ternary positive electrode material.

10. The cathode electrode according to claim 9, wherein 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 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, and element R comprises one or more of N, F, S or Cl.

11. The cathode electrode according to claim 9 or 10, wherein The lithium-containing phosphate comprises an Fe element, and the ternary positive electrode material comprises an Mn element; and the mass ratio of the Fe element to the Mn element in the positive electrode active material layer is 0.03-0.

25.

12. The cathode electrode of claim 11, wherein, The mass ratio of the Fe element to the Mn element in the positive electrode active material layer is 0.05-0.

20.

13. The cathode sheet of claim 9, wherein, The positive electrode active material further comprises at least one coating layer covering at least 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.

14. The cathode sheet of claim 1, wherein, The positive electrode tab further comprises a hydrophobic conductive layer, the hydrophobic conductive layer is located between the first positive electrode active material layer and the second positive electrode active material layer, and the hydrophobic conductive layer comprises a hydrophobic conductive material.

15. The cathode electrode of claim 14, wherein, The hydrophobic conductive material comprises a hydrophobic conductive polymer and a hydrophobic conductive carbon.

16. The cathode electrode according to claim 15, wherein The hydrophobic conductive polymer comprises one or more of polypyrrole, polyaniline, polythiophene or polyacetylene; And / or The hydrophobic conductive carbon comprises one or more of hydrophobic carbon nanotubes or hydrophobic carbon nanofibers.

17. The cathode sheet of claim 15 or 16, wherein, In the hydrophobic conductive material, the mass ratio of the hydrophobic conductive carbon is 2%-10%.

18. A battery, characterized by The battery comprises the positive electrode tab as claimed in any one of claims 1-17.

19. An electrical device, comprising: The battery comprises the positive electrode tab as claimed in claim 18.

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