CN115939305A

CN115939305A - Positive plate and preparation method thereof, electrode assembly, battery monomer, battery and electric equipment

Info

Publication number: CN115939305A
Application number: CN202210971925.5A
Authority: CN
Inventors: 李静如; 史松君; 来佑磊; 朱映华; 童星; 鲁志远
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-08-12
Filing date: 2022-08-12
Publication date: 2023-04-07

Abstract

The application relates to a positive plate and a preparation method thereof, an electrode assembly, a battery monomer, a battery and electric equipment, and belongs to the technical field of secondary batteries. The positive active material layer of the positive plate comprises a first positive active material layer and a second positive active material layer which are covered on the surface of a positive current collector and are sequentially arranged outwards, wherein a first positive active material in the first positive active material layer comprises a compound represented by the chemical formula LiNi _x1 Mn _(1‑x1) O ₂ The x1 is more than 0 and less than 1; the second positive electrode active material in the second positive electrode active material layer includes a material having a chemical formula of LiFe _x2 Mn _(1‑x2) PO ₄ X2 is more than 0 and less than 1; wherein, the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micron level. The capacity of the positive plate can be ensured, the capacity retention rate is improved, the gas generation is reduced, the service life of the battery is prolonged, and the cost can be reduced.

Description

Positive plate and preparation method thereof, electrode assembly, battery monomer, battery and electric equipment

Technical Field

The application relates to the technical field of secondary batteries, in particular to a positive plate, a preparation method of the positive plate, an electrode assembly, a battery monomer, a battery and electric equipment.

Background

In the existing lithium ion battery, the cathode material is usually a ternary material, for example: lithium nickel cobalt manganese oxide Li (NiCoMn) O ₂ The material contains cobalt, and the cobalt plays a key role in the dynamics and stability of the anode material. However, only part of cobalt participates in electrochemical reaction, the content of nickel is reduced by the existence of cobalt, the energy density is reduced, and the cost of cobalt is higher.

Disclosure of Invention

Aiming at the defects of the prior art, the application provides a positive plate and a preparation method thereof, an electrode assembly, a battery monomer, a battery and electric equipment so as to reduce the use amount of cobalt.

In a first aspect, an embodiment of the present application provides a positive plate, including a positive current collector and a positive active material layer, where the positive active material layer includes a first positive active material layer and a second positive active material layer that are covered on a surface of the positive current collector and are sequentially disposed outward, and a first positive active material in the first positive active material layer includes a positive electrode material having a chemical formula of LiNi _x1 Mn _(1-x1) O ₂ The x1 is more than 0 and less than 1; the second positive electrode active material in the second positive electrode active material layer includes a material having a chemical formula of LiFe _x2 Mn _(1-x2) PO ₄ X2 is more than 0 and less than 1; wherein, the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micron level.

In the technical scheme of the embodiment of the application, liNi is used _x1 Mn _(1-x1) O ₂ The cobalt-free material is used as the anode active material, so that the use amount of cobalt can be reduced, and the cost of the anode active material is reduced; meanwhile, the Dv50 of the cobalt-free material is nano-scale, and compared with the conventional cobalt-free material, the rapid charging capacity of the cobalt-free material is improved; meanwhile, the upper layer of the cobalt-free material is provided with LiFe with a chemical formula _x2 Mn _(1-x2) PO ₄ The Dv50 of the lithium iron manganese phosphate material is micron-sized, which can reduce the probability of direct contact between the cobalt-free material and the electrolyte to a certain extent, reduce gas generation, improve the stability of the positive plate, reduce gas generation while ensuring the capacity retention rate of the positive plate, and reduce cost.

In some embodiments, the Dv50 for the cobalt-free material is between 100nm and 300nm, and the Dv50 for the lithium iron manganese phosphate material is between 1 μm and 3 μm. The cobalt-free material with the particle size has high capacity, poor stability, low capacity retention rate and obvious gas generation; when the lithium iron manganese phosphate material is used together with the lithium iron manganese phosphate material with the particle size, the problem of gas generation can be well solved, the stability and the safety of the positive plate can be further improved, and the capacity retention rate is higher.

In some embodiments, the cobalt-free material is present in the first positive electrode active material and the second positive electrode active material at a ratio of 20% to 80% by mass. The addition amount of the cobalt-free material is within the range, so that the capacity retention rate of the positive plate is further improved while the capacity of the positive plate is higher, and the problem of gas generation is well improved.

In some embodiments, the first positive electrode active material further comprises a material having the chemical formula LiNi _x3 Co _y3 Mn _1-x3-y3 O ₂ Wherein x3 is more than or equal to 0.5 and less than 1, y3 is more than 0 and less than or equal to 0.05, and the mass ratio of the low cobalt material in the first positive electrode active material is not more than 30%. A small amount of low-cobalt material can be added into the first active material, so that the stability of the first positive electrode active material layer can be improved, and the capacity retention rate of the positive electrode plate can be further improved.

In some embodiments, the absolute value of the difference between the voltage plateau of the first positive electrode active material and the voltage plateau of the second positive electrode active material is ≦ 0.3V. The difference value between the voltage platforms of the anode plate and the cathode plate is smaller, so that the stability and the energy density of the anode plate can be higher.

In some embodiments, 0.2 ≦ x2 ≦ 0.8. X2 in the lithium iron manganese phosphate material meets the conditions, so that the stability and the energy density of the positive plate are high.

In some embodiments, the second positive active material comprises LiFe _0.5 Mn _0.5 PO ₄ And the chemical formula is LiFe _0.3 Mn _0.7 PO ₄ Lithium manganese iron phosphate material, liFe _0.3 Mn _0.7 PO ₄ The mass ratio of the material in the second positive electrode active material is not higher than 30%. When the Dv50 of the cobalt-free material is within the range of 100nm to 300nm, the lithium iron manganese phosphate material is prepared by using the materials of the two chemical formulas, and the content of the lithium iron manganese phosphate material satisfies the range, so that the stability of an electrode assembly containing the positive plate is high, and the energy density of the electrode assembly is improved to a certain extent.

In some embodiments, at least a portion of the surface of the first cathode active material is coated with a first configuration conductive polymer layer, the mass of the first configuration conductive polymer layer being 0.5% to 3% of the total mass of the first cathode active material and the first configuration conductive polymer layer. The first structure type conductive polymer is coated on the surface of the first positive electrode active material, so that the ionic conductivity and/or electronic conductivity of the first positive electrode active material can be improved, and the ionic conductivity and/or electronic conductivity of the first positive electrode active material layer can be enhanced.

In some embodiments, at least a portion of a surface of the second cathode active material is coated with a second structure-type conductive polymer layer, and a mass of the second structure-type conductive polymer layer is 0.5% to 3% of a total mass of the second cathode active material and the second structure-type conductive polymer layer. The second structure type conductive polymer is coated on the surface of the second positive electrode active material, so that the ionic conductivity and/or electronic conductivity of the second positive electrode active material can be improved, and the ionic conductivity and/or electronic conductivity of the second positive electrode active material layer can be enhanced.

In some embodiments, the material of the first structural-type conductive polymer layer and/or the material of the second structural-type conductive polymer layer includes an ionic polymer and an electronic polymer. The ionic conduction and electronic conduction performances of the positive active material can be enhanced, and the rate capability of the positive active material is improved.

In some embodiments, the ionic polymer comprises at least one of polyethylene glycol, polyethylene oxide, polyethylene succinate, polyethylene glycol imine.

In some embodiments, the electronic polymer comprises at least one of polyaniline, polythiophene, polypyrrole, and polyacene.

In some embodiments, the material of the first structural conductive polymer layer and/or the material of the second structural conductive polymer layer is a mixture of polyaniline and polyethylene glycol, and the mass ratio of the polyaniline in the mixture is 30-70%. The ionic conduction and electronic conduction performances of the positive active material can be well enhanced, so that the rate capability of the positive active material is improved.

In some embodiments, the weight average molecular weight of the polyaniline is 20000 to 80000, and the structural formula of the polyaniline is:

wherein y =0.5. Polyaniline is in an intermediate oxidation state with the same number of oxidation units and reduction units, and has better electronic conduction effect.

In some embodiments, the polyethylene glycol has a weight average molecular weight of 800 to 4000.

In a second aspect, the present application provides an electrode assembly comprising a negative electrode tab, a separator and any one of the positive electrode tabs provided in the first aspect, wherein the separator is disposed between the positive electrode tab and the negative electrode tab.

In the technical scheme of the embodiment of the application, the electrode assembly formed by using the positive plate has the advantages of high capacity retention rate, low gas generation rate and low cost.

In a third aspect, the present application provides a battery cell comprising the electrode assembly provided in the second aspect.

In a fourth aspect, the present application provides a battery including the battery cell provided in the third aspect.

In a fifth aspect, the present application provides an electrical device comprising the battery provided in the fourth aspect.

In a sixth aspect, the present application provides a method for preparing a positive electrode sheet, including the steps of: coating the first positive active slurry on the surface of a positive current collector to form a first positive active material layer, wherein the first positive active material in the first positive active slurry comprises LiNi _x1 Mn _(1-x1) O ₂ The cobalt-free material has 0 < x1 < 1. Coating the second positive electrode active slurry on the surface of the first positive electrode active material layer to form a second positive electrode active material layer, wherein the second positive electrode active material in the second positive electrode active slurry comprises LiFe with a chemical formula _x2 Mn _(1-x2) PO ₄ The x2 of the lithium iron manganese phosphate material is more than 0 and less than 1. The Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micrometer level.

In the technical scheme of this application embodiment, through the mode of double-deck coating, form the first positive pole active material layer that contains the cobalt-free material in the positive pole active material and is close to the mass flow body to and contain the second positive pole active material layer of lithium iron manganese phosphate material in the positive pole active material, second positive pole active material layer covers on first positive pole active material layer. The capacity retention rate of the positive plate can be ensured, the gas generation is reduced, and the cost can be reduced.

In some embodiments, the ratio of the coating weight of the first positive electrode active material to the coating weight of the second positive electrode active material is (2-8) to (8-2). The coating weight of the first positive electrode active material and the second positive electrode active material meets the proportion, so that the positive electrode plate has better comprehensive performance in three aspects of capacity retention rate improvement, gas generation reduction, cost reduction and the like.

In some embodiments, before the coating of the first cathode active material slurry, a step of coating at least a part of the surface of the first cathode active material with a first conductive polymer layer in a bonding configuration is further included. The surface of the first positive electrode active material is coated with the first conductive polymer layer with a structure, so that the ionic conduction and/or electronic conduction performance of the first positive electrode active material can be improved, and the ionic conduction and/or electronic conduction performance of the first positive electrode active material layer can be enhanced.

In some embodiments, before coating the second cathode active material, a step of coating a second structure type conductive polymer layer on at least a part of the surface of the second cathode active material is further included. The surface of the second positive electrode active material is coated with the second structure type conductive polymer layer, so that the ion conductivity and/or the electron conductivity of the second positive electrode active material can be improved, and the ion conductivity and/or the electron conductivity of the second positive electrode active material layer can be enhanced.

In some embodiments, a method of cladding a first structured conductive polymer layer, comprises: the first positive electrode active material, the first structural conductive polymer, and the solvent are uniformly mixed and then dried. Through the mode of mixing cladding, the cladding is comparatively simple, realizes easily.

In some embodiments, a method of cladding a second structured conductive polymer layer, comprises: the second positive electrode active material, the second structure type conductive polymer, and the solvent are uniformly mixed and then dried. Through the mode of mixing cladding, the cladding is comparatively simple, realizes easily.

In some embodiments, a method of cladding a first structured conductive polymer layer, comprises: uniformly mixing a first positive electrode active material, a first configuration conductive polymer monomer, an initiator and a solvent, crosslinking the first configuration conductive polymer monomer on at least part of the surface of the first positive electrode active material to form a first configuration conductive polymer, and drying. The structure type conductive polymer layer is formed in a coating and polymerization mode, the layer structure is compact, and the ion conductivity or/and electron conductivity performance is good.

In some embodiments, a method of cladding a second structured conductive polymer layer, comprises: uniformly mixing a second positive electrode active material, a second structure type conducting polymer monomer, an initiator and a solvent, crosslinking the second structure type conducting polymer monomer on at least part of the surface of the second positive electrode active material to form a second structure type conducting polymer, and then drying. The structure type conductive polymer layer is formed in a coating and polymerization mode, the layer structure is compact, and the ion conductivity or/and electron conductivity performance is good.

The foregoing description is only an overview of the technical solutions of the present application, and the present application can be implemented according to the content of the description in order to make the technical means of the present application more clearly understood, and the following detailed description of the present application is given in order to make the above and other objects, features, and advantages of the present application more clearly understandable.

Drawings

Various additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Moreover, like reference numerals are used to refer to like elements throughout. In the drawings:

FIG. 1 is a schematic structural diagram of a vehicle provided in some embodiments of the present application;

fig. 2 is an exploded view of a battery according to some embodiments of the present disclosure;

fig. 3 is a schematic structural diagram of a battery cell according to some embodiments of the present disclosure;

fig. 4 is an exploded view of a battery cell provided in accordance with some embodiments of the present application;

fig. 5 is a schematic diagram of a first layer structure of a positive electrode sheet provided in some embodiments of the present application;

fig. 6 is a schematic view of a second layer structure of a positive electrode sheet provided in some embodiments of the present application;

fig. 7 is a flow chart of a process for preparing a positive electrode sheet according to some embodiments of the present disclosure.

An icon: 1000-a vehicle; 100-a battery; 10-a box body; 11-an accommodation space; 12-a first part; 13-a second part; 20-a battery cell; 21-a housing; 211-an opening; 22-an end cap assembly; 221-end cap; 222-electrode terminals; 23-an electrode assembly; 231-positive plate; 2311-positive current collector; 2312-positive active material layer; 2312 a-a first positive electrode active material layer; 2312 b-a second positive electrode active material layer; 24-a current collecting member; 25-an insulating protection; 200-a controller; 300-motor.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are merely used to more clearly illustrate the technical solutions of the present application, and therefore are only examples, and the protection scope of the present application is not limited thereby.

Unless defined otherwise, 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 application; the terms "including" and "having," and any variations thereof, in the description and claims of this application and the description of the above figures are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first", "second", and the like are used only for distinguishing different objects, and are not to be construed as indicating or implying relative importance or to implicitly indicate the number, specific order, or primary-secondary relationship of the technical features indicated. In the description of the embodiments of the present application, "a plurality" means two or more unless specifically defined otherwise.

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 appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is only one kind of association relationship describing an associated object, and means that three relationships may exist, for example, a and/or B, and may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.

In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two), and similarly, "plural sets" refers to two or more (including two sets), "plural pieces" refers to two or more (including two pieces).

In the description of the embodiments of the present application, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like, indicate the directions or positional relationships indicated in the drawings, and are only for convenience of description of the embodiments of the present application and for simplicity of description, but do not indicate or imply that the referred device or element must have a specific direction, be constructed and operated in a specific direction, and thus, should not be construed as limiting the embodiments of the present application.

In the description of the embodiments of the present application, unless otherwise explicitly specified or limited, the terms "mounted," "connected," "fixed," and the like are to be construed broadly, e.g., as meaning fixedly connected, detachably connected, or integrated; mechanical connection or electrical connection is also possible; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the embodiments of the present application can be understood by those of ordinary skill in the art according to specific situations.

At present, the application of power batteries is more and more extensive from the development of market conditions. The power battery is not only applied to energy storage power supply systems such as hydraulic power, firepower, wind power and solar power stations, but also widely applied to electric vehicles such as electric bicycles, electric motorcycles, electric automobiles and the like, and a plurality of fields such as military equipment and aerospace. With the continuous expansion of the application field of the power battery, the market demand is also continuously expanding.

The power battery can be a lithium ion battery, and in the charging process of the lithium ion battery, lithium ions are separated from the positive active material, transmitted through the electrolyte, pass through the isolating membrane and are embedded into the negative active material. Currently, the positive active material is generally a ternary material, such as: lithium nickel cobalt manganese oxide Li (NiCoMn) O ₂ The material, in which Ni is mainly used for improving the energy density of the battery, mn is mainly used for improving the stability of the battery, and Co is mainly used for improving the dynamics and stability of the battery. However, only part of cobalt participates in electrochemical reaction, the content of nickel is reduced by the existence of cobalt, the energy density is reduced, and the cost of cobalt is higher.

Therefore, the present application intends to use a positive electrode active material (chemical formula LiNi) _x1 Mn _(1-x1) O ₂ Cobalt-free material) instead of the existing lithium nickel cobalt manganese oxide Li (NiCoMn) O ₂ The material is used. The inventor researches and discovers that the cobalt-free material (Li (NiCoMn) O) ₂ ) If it is prepared into small particles, the kinetics of the cobalt-free material can be improved, but when the small particles of the cobalt-free material are in direct contact with the electrolyte, the problem of gas evolution deterioration occurs.

Based on the above consideration, in order to use a compound represented by the chemical formula LiNi _x1 Mn _(1-x1) O ₂ The inventors of the present invention have made extensive studies to design a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer includes a first positive electrode active material layer 2312a and a second positive electrode active material layer which are sequentially disposed to the outside and cover the surface of the positive electrode current collector, and the first positive electrode active material in the first positive electrode active material layer includes a compound represented by LiNi _x1 Mn _(1-x1) O ₂ The x1 is more than 0 and less than 1; the second positive electrode active material in the second positive electrode active material layer includes a material having a chemical formula of LiFe _x2 Mn _(1-x2) PO ₄ X2 is more than 0 and less than 1; wherein, the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micron level.

In such a positiveIn the pole piece, liNi is used _x1 Mn _(1-x1) O ₂ The cobalt-free material is used as the anode active material, so that the use amount of cobalt can be reduced, and the cost of the anode active material is reduced; meanwhile, the Dv50 of the cobalt-free material is nano-scale, so that the quick charging capacity of the cobalt-free material is improved compared with that of a conventional cobalt-free material; meanwhile, the upper layer of the cobalt-free material is provided with LiFe with the chemical formula _x2 Mn _(1-x2) PO ₄ The Dv50 of the lithium iron manganese phosphate material is micron-sized, which can reduce the probability of direct contact between the cobalt-free material and the electrolyte to a certain extent, reduce gas generation, improve the stability of the positive plate, reduce gas generation while ensuring the capacity retention rate of the positive plate, and reduce cost.

The positive electrode sheet can be used for preparing an electrode assembly which can be used in electric equipment such as vehicles, ships or aircrafts, but is not limited to the above. The power supply system with the battery monomer, the battery and the like can be used, so that the capacity is improved, the gas generation problem is improved, and the cost is reduced.

The embodiment of the application provides an electric device using a battery as a power supply, wherein the electric device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool and the like. The vehicle can be a fuel oil vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle can be a pure electric vehicle, a hybrid electric vehicle or a range extending vehicle and the like; spacecraft include aircraft, rockets, space shuttles, spacecraft, and the like; electric toys include stationary or mobile electric toys, such as game machines, electric car toys, electric ship toys, electric airplane toys, and the like; the electric power tools include metal cutting electric power tools, grinding electric power tools, assembly electric power tools, and electric power tools for railways, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, electric impact drills, concrete vibrators, and electric planers. The embodiment of the present application does not particularly limit the above electric devices.

For convenience of explanation, the following embodiments will be described by taking an electric device as an example of a vehicle.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a vehicle 1000 according to some embodiments of the present disclosure. The battery 100 is provided inside the vehicle 1000, and the battery 100 may be provided at the bottom or the head or the tail of the vehicle 1000. The battery 100 may be used for power supply of the vehicle 1000, for example, the battery 100 may serve as an operation power source of the vehicle 1000.

The vehicle 1000 may further include a controller 200 and a motor 300, the controller 200 being configured to control the battery 100 to supply power to the motor 300, for example, for starting, navigation, and operational power requirements while the vehicle 1000 is traveling.

In some embodiments of the present application, the battery 100 may be used not only as an operating power source of the vehicle 1000, but also as a driving power source of the vehicle 1000, instead of or in part of fuel or natural gas, to provide driving power for the vehicle 1000.

Fig. 2 is an exploded view of the battery 100 according to some embodiments of the present disclosure. Referring to fig. 2, the battery 100 includes a case 10 and a battery cell 20, and the battery cell 20 is accommodated in the case 10.

The case 10 is used to provide a receiving space 11 for the battery cell 20. In some embodiments, the case 10 may include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 are mutually covered to define a receiving space 11 for receiving the battery cell 20. Of course, the joint between the first part 12 and the second part 13 can be sealed by a sealing member (not shown), which can be a sealing ring, a sealant, etc.

The first and second portions 12, 13 may be a variety of shapes, such as rectangular parallelepiped, cylindrical, etc. The first portion 12 may be a hollow structure with one side opened to form an accommodating cavity for accommodating the battery cell 20, the second portion 13 may also be a hollow structure with one side opened to form an accommodating cavity for accommodating the battery cell 20, and the opening side of the second portion 13 covers the opening side of the first portion 12 to form the box 10 with the accommodating space 11. Of course, as shown in fig. 2, the first portion 12 may have a hollow structure with one side open, the second portion 13 may have a plate-like structure, and the second portion 13 may cover the open side of the first portion 12 to form the box 10 having the accommodating space 11.

In the battery 100, one or more battery cells 20 may be provided. If there are a plurality of battery cells 20, the plurality of battery cells 20 may be connected in series, in parallel, or in series-parallel, where in series-parallel refers to that the plurality of battery cells 20 are connected in series or in parallel. The plurality of battery cells 20 can be directly connected in series or in parallel or in series-parallel, and the whole formed by the plurality of battery cells 20 is accommodated in the box body 10; of course, a plurality of battery cells 20 may be connected in series, in parallel, or in series-parallel to form a battery module, and a plurality of battery modules may be connected in series, in parallel, or in series-parallel to form a whole and be accommodated in the box 10. The battery cell 20 may be cylindrical, flat, rectangular parallelepiped, or other shape. Fig. 2 exemplarily shows a case where the battery cell 20 has a square shape.

In some embodiments, the battery 100 may further include a bus member (not shown), and the plurality of battery cells 20 may be electrically connected to each other through the bus member, so as to connect the plurality of battery cells 20 in series or in parallel or in series-parallel.

Fig. 3 is a schematic structural diagram of a battery cell 20 according to some embodiments of the present disclosure, and fig. 4 is an exploded view of the battery cell 20 according to some embodiments of the present disclosure. Referring to fig. 3 and 4, the battery cell 20 may include a case 21, an end cap assembly 22, and an electrode assembly 23. The case 21 has an opening 211, the electrode assembly 23 is accommodated in the case 21, and the cap assembly 22 is used to cover the opening 211.

The shape of the case 21 may be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 has a rectangular parallelepiped structure, the case 21 may have a rectangular parallelepiped structure. Fig. 3 and 4 exemplarily show a case 21 and an electrode assembly 23 in a square shape.

The material of the housing 21 may be various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present invention is not limited thereto.

The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is adapted to cover the opening 211 of the case 21 to form a sealed installation space (not shown) for accommodating the electrode assembly 23. The installation space is also used for accommodating an electrolyte, for example an electrolyte. The end cap assembly 22 is used as a component for outputting electric energy of the electrode assembly 23, and the electrode terminal 222 in the end cap assembly 22 is used for electrically connecting with the electrode assembly 23, that is, the electrode terminal 222 is electrically connected with a tab of the electrode assembly 23, for example, the electrode terminal 222 and the tab are connected through the current collecting member 24, so as to electrically connect the electrode terminal 222 with the tab.

One or two openings 211 of the housing 21 may be provided. If the opening 211 of the case 21 is one, the end cap assembly 22 may be one, and two electrode terminals 222 may be disposed in the end cap assembly 22, and the two electrode terminals 222 are respectively used for electrically connecting with the positive electrode tab and the negative electrode tab of the electrode assembly 23. If there are two openings 211 of the housing 21, for example, two openings 211 are disposed on two opposite sides of the housing 21, the end cover assemblies 22 may also be two, and the two end cover assemblies 22 respectively cover the two openings 211 of the housing 21. In this case, it may be that the electrode terminal 222 in one end cap assembly 22 is a positive electrode terminal for electrical connection with a positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 is a negative electrode terminal for electrical connection with the negative electrode tab of the electrode assembly 23.

In some embodiments, as shown in fig. 4, the battery cell 20 may further include an insulation protector 25 fixed to the outer circumference of the electrode assembly 23, the insulation protector 25 serving to insulate and isolate the electrode assembly 23 from the case 21. Illustratively, the insulating protector 25 is an adhesive tape that is bonded to the outer circumference of the electrode assembly 23. In some embodiments, the number of the electrode assemblies 23 is plural, the insulating protector 25 surrounds the outer circumferences of the plural electrode assemblies 23, and the plural electrode assemblies 23 are formed in an integral structure to keep the electrode assemblies 23 structurally stable.

The electrode assembly 23 includes a positive electrode tab, a negative electrode tab, and a separator. The positive plate comprises a positive current collector and a positive active material layer, the positive active material layer is coated on the surface of the positive current collector, the positive current collector which is not coated with the positive active material layer protrudes out of the positive current collector which is coated with the positive active material layer, and the positive current collector which is not coated with the positive active material layer is used as a positive electrode tab.

The negative plate comprises a negative current collector and a negative active substance layer, the negative active substance layer is coated on the surface of the negative current collector, the negative current collector which is not coated with the negative active substance layer protrudes out of the negative current collector which is coated with the negative active substance layer, and the negative current collector which is not coated with the negative active substance layer is used as a negative pole tab. The material of the negative electrode collector may be copper, and the negative electrode active material may be carbon, silicon, or the like. In order to ensure that the fuse is not fused when a large current is passed, the number of the positive electrode tabs is multiple and the positive electrode tabs are stacked together, and the number of the negative electrode tabs is multiple and the negative electrode tabs are stacked together. The material of the isolation film may be PP (polypropylene) or PE (polyethylene). In addition, the electrode assembly 23 may be a winding type electrode assembly or a laminated type electrode assembly, and the embodiment of the present application is not limited thereto.

Fig. 5 is a schematic view of a first layer structure of a positive electrode sheet 231 provided in some embodiments of the present application, and fig. 6 is a schematic view of a second layer structure of the positive electrode sheet 231 provided in some embodiments of the present application; referring to fig. 5 and 6, the positive plate 231 includes a positive current collector 2311 and a positive active material layer 2312, the positive active material layer 2312 includes a first positive active material layer 2312a and a second positive active material layer 2312b covering the surface of the positive current collector 2311 and sequentially disposed outward, and the first positive active material in the first positive active material layer 2312a includes LiNi _x1 Mn _(1-x1) O ₂ The x1 is more than 0 and less than 1; the second positive electrode active material in the second positive electrode active material layer 2312b includes a material having a chemical formula of LiFe _x2 Mn _(1-x2) PO ₄ X2 is more than 0 and less than 1; wherein, the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micron level.

The material of the positive current collector 2311 may be one or more of aluminum, aluminum alloy, nickel alloy, titanium alloy, silver, and silver alloy. With continued reference to fig. 5, in one embodiment, a first positive active material layer 2312a and a second positive active material layer 2312b are sequentially disposed on one surface of the positive current collector 2311; with continued reference to fig. 6, in another embodiment, a first positive active material layer 2312a and a second positive active material layer 2312b are sequentially disposed on both surfaces of the positive current collector 2311.

The first positive electrode active material layer 2312a refers to a layer in contact with the positive electrode current collector 2311; the second cathode active material layer 2312b refers to a layer in contact with a surface of the first cathode active material layer 2312a facing away from the cathode current collector 2311. The "active material" in the first positive electrode active material and the second positive electrode active material refers to a substance capable of releasing or absorbing lithium ions.

Nanoscale means that: particles with the particle size of 1 nm-500 nm; micron-scale means: 0.5-10 μm. The Dv50 of the cobalt-free material is nanoscale: the cobalt-free material particles are added from small to large, when the cobalt-free material particles account for 50% of the total volume, the particle size of the cobalt-free material particles is the value of Dv50, and the value of Dv50 is between 1nm and 500 nm. The Dv50 of the lithium iron manganese phosphate material is micron-sized: accumulating the lithium iron manganese phosphate particles from small to large, wherein when the particles are accumulated to 50% of the total volume, the particle size of the lithium iron manganese phosphate particles is a Dv50 value, and the Dv50 value is between 0.5 and 10 mu m.

In the technical scheme of the embodiment of the application, liNi is used _x1 Mn _(1-x1) O ₂ The cobalt-free material is used as the anode active material, so that the use amount of cobalt can be reduced, and the cost of the anode active material is reduced; meanwhile, the Dv50 of the cobalt-free material is nano-scale, and compared with the conventional cobalt-free material, the rapid charging capacity of the cobalt-free material is improved; meanwhile, the upper layer of the cobalt-free material is provided with LiFe with a chemical formula _x2 Mn _(1-x2) PO ₄ The second positive active material layer is formed by the lithium manganese iron phosphate material, and the Dv50 of the lithium manganese iron phosphate material is micron-sized, so that the probability of direct contact between the cobalt-free material and the electrolyte can be reduced to a certain extent, the gas generation is reduced, the stability of the positive plate 231 is improved, the gas generation is reduced while the capacity retention rate of the positive plate 231 is ensured, and the cost can be reduced.

Optionally, the cobalt-free material comprises LiNi _0.1 Mn _0.9 O ₂ 、LiNi _0.2 Mn _0.8 O ₂ 、LiNi _0.3 Mn _0.7 O ₂ 、LiNi _0.4 Mn _0.6 O ₂ 、LiNi _0.5 Mn _0.5 O ₂ 、LiNi _0.6 Mn _0.4 O ₂ 、LiNi _0.7 Mn _0.3 O ₂ 、LiNi _0.8 Mn _0.2 O ₂ 、LiNi _0.9 Mn _0.1 O ₂ One or more of, liNi _x1 Mn _(1-x1) O ₂ X1 in (b) may be any one or more values (other than 0 and 1) in the range of 0 to 1.

Optionally, the lithium iron manganese phosphate material comprises LiFe _0.1 Mn _0.9 PO ₄ 、LiFe _0.2 Mn _0.8 PO ₄ 、LiFe _0.3 Mn _0.7 PO ₄ 、LiFe _0.4 Mn _0.6 PO ₄ 、LiFe _0.5 Mn _0.5 PO ₄ 、LiFe _0.6 Mn _0.4 PO ₄ 、LiFe _0.7 Mn _0.3 PO ₄ 、LiFe _0.8 Mn _0.2 PO ₄ 、LiFe _0.9 Mn _0.1 PO ₄ One or more of (a), liFe _x2 Mn _(1-x2) PO ₄ X2 in (b) may be any one or more values (other than 0 and 1) in the range of 0 to 1.

In some embodiments, the Dv50 for the cobalt-free material is between 100nm and 300nm, and the Dv50 for the lithium iron manganese phosphate material is between 1 μm and 3 μm. The cobalt-free material with the particle size has high capacity, poor stability, low capacity retention rate and obvious gas generation; when the lithium iron manganese phosphate material is used in combination with the lithium iron manganese phosphate material with the particle size, the problem of gas generation can be well solved, and the stability and the safety of the positive plate 231 can be further improved while the capacity is high.

Illustratively, the Dv50 of the cobalt-free material is 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm or 300nm, which may also be any value in the range of 100nm to 300 nm. The Dv50 of the lithium iron manganese phosphate material is 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, or 3 μm, and may be any value within a range of 1 μm to 3 μm.

In some embodiments, the cobalt-free material is present in the first positive electrode active material and the second positive electrode active material at a mass ratio of 20% to 80%. Wherein the mass of the cobalt-free material/(the mass of the first positive electrode active material + the mass of the second positive electrode active material) × 100% =20% to 80%. The first positive electrode active material comprises a cobalt-free material and optionally other active materials; the second positive active material includes a lithium iron manganese phosphate material and optionally other active materials. When the amount of the cobalt-free material added is within the above range, the capacity of the positive electrode sheet 231 can be increased, the capacity retention rate can be further increased, and the problem of gas generation can be improved.

Illustratively, the mass ratio of the cobalt-free material in the first positive electrode active material and the second positive electrode active material is 20%, 30%, 40%, 50%, 60%, 70%, or 80%, which may be any value in the range of 20% to 80%.

In this application, the first positive electrode active material in the first positive electrode active material layer 2312a is not limited to a cobalt-free material, and some low-cobalt material or other positive electrode active material may be added, which is not limited in this application.

In some embodiments, the first positive active material further comprises a compound of formula LiNi _x3 Co _y3 Mn _1-x3-y3 O ₂ Wherein x3 is more than or equal to 0.5 and less than 1, y3 is more than 0 and less than or equal to 0.05, and the mass ratio of the low cobalt material in the first positive electrode active material is not more than 30%. A small amount of low-cobalt material may be added to the first active material, so that the stability of the first positive electrode active material layer may be improved, and the capacity retention rate of the positive electrode sheet 231 may be further improved.

Optionally, the low cobalt material comprises LiNi _0.5 Co _0.01 Mn _0.49 O ₂ 、LiNi _0.6 Co _0.02 Mn _0.38 O ₂ 、LiNi _0.7 Co _0.03 Mn _0.27 O ₂ 、LiNi _0.8 Co _0.04 Mn _0.16 O ₂ 、LiNi _0.9 Co _0.05 Mn _0.05 O ₂ 、LiNi _0.5 Co _0.05 Mn _0.45 O ₂ 、LiNi _0.6 Co _0.04 Mn _0.36 O ₂ 、LiNi _0.7 Co _0.02 Mn _0.28 O ₂ 、LiNi _0.8 Co _0.02 Mn _0.18 O ₂ 、LiNi _0.9 Co _0.01 Mn _0.09 O ₂ One or more of, liNi _x3 Co _y3 Mn _1-x3-y3 O ₂ X3 in (b) may be any one or more values (other than 1) in the range of 0.5 to 1, and y3 may be any one or more values (other than 0) in the range of 0 to 0.05.

Illustratively, the mass ratio of the low cobalt material in the first positive electrode active material is 0.5%, 1%, 2%, 4%, 8%, 12%, 16%, 20%, 24%, 28%, or 30%, and it may be any value in the range of 0 to 30% (when 0% is added, the low cobalt material is not included in the first positive electrode active material).

In some embodiments, the absolute value of the difference between the voltage plateau of the first positive electrode active material and the voltage plateau of the second positive electrode active material is ≦ 0.3V. The difference between the voltage levels is small, and the stability and energy density of the positive electrode sheet 231 can be increased.

Alternatively, the voltage plateau of the first positive electrode active material-the voltage plateau of the second positive electrode active material = -0.3, -0.2, -0.1, 0, 0.1, 0.2, or 0.3, which may also be any value from-0.3 to 0.3.

In some embodiments, 0.2 ≦ x2 ≦ 0.8. X2 in the lithium iron manganese phosphate material satisfies the above conditions, and the stability and energy density of the positive plate 231 can be high. Illustratively, the lithium iron manganese phosphate material comprises LiFe _0.2 Mn _0.8 PO ₄ 、LiFe _0.3 Mn _0.7 PO ₄ 、LiFe _0.4 Mn _0.6 PO ₄ 、LiFe _0.5 Mn _0.5 PO ₄ 、LiFe _0.6 Mn _0.4 PO ₄ 、LiFe _0.7 Mn _0.3 PO ₄ 、LiFe _0.8 Mn _0.2 PO ₄ One or more of (a), liFe _x2 Mn _(1-x2) PO ₄ X2 in (b) may be any one or more values in the range of 0.2 to 0.8.

In some embodiments, the second positive active material comprises a material having a chemical formula of LiFe _0.5 Mn _0.5 PO ₄ And the chemical formula is LiFe _0.3 Mn _0.7 PO ₄ Lithium iron manganese phosphate material, liFe _0.3 Mn _0.7 PO ₄ The mass ratio of the material in the second positive electrode active material is not higher than 30%. When the Dv50 of the cobalt-free material is within the range of 100nm to 300nm, the lithium iron manganese phosphate material is prepared by using the materials of the two formulae, and the contents thereof satisfy the above range, so that the stability of the electrode assembly 23 including the positive electrode sheet 231 can be improved, and the energy density thereof can be improved to a certain extent.

By way of example, liFe _0.3 Mn _0.7 PO ₄ The mass ratio of the material in the second positive electrode active material is 0.5%, 1%, 2%, 4%, 8%, 12%, 16%, 20%, 24%, 28%, or 30%, and it may be any value in the range of 0 to 30% (when 0% is added, liFe is not contained in the second positive electrode active material _0.3 Mn _0.7 PO ₄ )。

In other embodiments, the second positive electrode active material may further include a small amount of lithium iron phosphate, and the mass ratio of the lithium iron phosphate in the second positive electrode active material is not higher than 10%.

In the present application, a small amount of other positive electrode active materials may be further added to the first positive electrode active material and/or the second positive electrode active material, for example: and other positive electrode active materials with the mass ratio not higher than 5%, and the application is not limited.

In some embodiments, at least a portion of the surface of the first cathode active material is coated with a first configuration conductive polymer layer, the mass of the first configuration conductive polymer layer being 0.5% to 3% of the total mass of the first cathode active material and the first configuration conductive polymer layer. Or/and at least part of the surface of the second positive electrode active material is coated with a second structure type conductive polymer layer, and the mass of the second structure type conductive polymer layer accounts for 0.5-3% of the total mass of the second positive electrode active material and the second structure type conductive polymer layer.

Wherein the first structure type conductive polymer and the second structure type conductive polymer refer to: a substance capable of functioning as ionic or electronic conductivity by itself. The structural conductive polymer is coated on the surface of the positive active material, so that the ionic conductivity and/or electronic conductivity of the positive active material can be improved, and the ionic conductivity and/or electronic conductivity of the positive active material layer 2312 is enhanced.

Optionally, in one embodiment, at least a portion of the surface of the first positive electrode active material is coated with a first structural conductive polymer layer; in another embodiment, at least a portion of the surface of the second positive electrode active material is coated with a second structured conductive polymer layer; in a third embodiment, at least a portion of the surface of the first positive electrode active material is coated with a first structured conductive polymer layer, and at least a portion of the surface of the second positive electrode active material is coated with a second structured conductive polymer layer. Wherein "at least a portion of the surface" means a portion of the surface or the entire surface.

The mass of the first configuration-type conductive polymer layer/(the sum of the mass of the first positive electrode active material and the first configuration-type conductive polymer layer) = (0.5% to 3%). Illustratively, the mass ratio of the first conductivity-type polymer layer in the sum of the first cathode active material and the first conductivity-type polymer layer is 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%, which may be any value in the range of 0.5% to 3%.

Mass of the second structure type conductive polymer layer/(mass sum of the second positive electrode active material and the second structure type conductive polymer layer) = (0.5% to 3%). Illustratively, the mass ratio of the second structure type conductive polymer layer to the sum of the second cathode active material and the second structure type conductive polymer layer is 0.5%, 1%, 1.5%, 2%, 2.5%, or 3%, which may be any value in the range of 0.5% to 3%.

In some embodiments, the material of the first structurally-conductive polymer layer and/or the material of the second structurally-conductive polymer layer comprises an ionic polymer and an electronic polymer. The ion conduction and electron conduction performance of the positive active material can be enhanced, and the rate capability of the positive active material is improved. In other embodiments, the material of the structurally conductive polymer layer is an ionic polymer or an electronic polymer.

The material of the first structure type conductive polymer layer and the material of the second structure type conductive polymer layer may be the same or different, and are not limited herein.

Optionally, the ionic polymer comprises at least one of polyethylene glycol, polyethylene oxide, polyethylene glycol succinate, polyethylene glycol imine.

Optionally, the electronic polymer comprises at least one of polyaniline, polythiophene, polypyrrole, and polyvanine.

In some embodiments, the material of the first structural conductive polymer layer and/or the material of the second structural conductive polymer layer is a mixture of polyaniline and polyethylene glycol, and the mass ratio of the polyaniline in the mixture is 30-70%. The ion conduction and electron conduction performance of the positive electrode active material can be well enhanced, so that the rate capability of the positive electrode active material is improved.

Illustratively, the mass ratio of polyaniline in the mixture of polyaniline and polyethylene glycol is 30%, 40%, 50%, 60%, or 70%, which may be any value in the range of 30% to 70%.

Illustratively, the weight average molecular weight of the polyaniline is 20000, 30000, 40000, 50000, 60000, 70000, or 80000, and may be any value within the range of 20000 to 80000.

In some embodiments, the polyethylene glycol has a weight average molecular weight of 800 to 4000. Illustratively, the polyethylene glycol has a weight average molecular weight of 800, 1000, 1500, 2000, 2500, 3000, 3500, or 4000, which may also be any value in the range of 800 to 4000.

After the foregoing description of the material and structure of the positive electrode plate 231, the following description will specifically describe the method for manufacturing the positive electrode plate 231.

The preparation method of the positive electrode sheet 231 includes the steps of: coating the first positive active paste on the surface of the positive current collector 2311 to form a first positive active material layer 2312a, wherein the first positive active material in the first positive active paste comprises a material with a chemical formula of LiNi _x1 Mn _(1-x1) O ₂ The cobalt-free material has 0 < x1 < 1. Coating the second positive active slurry on the surface of the first positive active material layer 2312a to form a second positive active material layer 2312b, wherein the second positive active material in the second positive active slurry comprises LiFe _x2 Mn _(1-x2) PO ₄ The x2 of the lithium iron manganese phosphate material is more than 0 and less than 1. Wherein, the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micron level.

In the technical solution of the embodiment of the present application, a first positive active material layer 2312a containing a cobalt-free material in the positive active material and close to the current collector and a second positive active material layer 2312b containing a lithium iron manganese phosphate material in the positive active material are formed by a double-layer coating method, and the second positive active material layer 2312b covers the first positive active material layer 2312a. The capacity retention rate of the positive plate 231 can be ensured, the gas generation can be reduced, and the cost can be reduced.

Fig. 7 is a flowchart of a process for preparing the positive electrode plate 231 according to some embodiments of the present application, and referring to fig. 7, a method for preparing the positive electrode plate 231 according to the embodiments of the present application includes the following steps:

s110, preparing first positive active slurry: the first positive electrode active material, the binder, and the conductive agent are dispersed in a solvent to form a first positive electrode active paste. The first positive electrode active material may be the first positive electrode active material described above, for example: has the chemical formula LiNi _x1 Mn _(1-x1) O ₂ (x 1 is more than 0 and less than 1), the Dv50 of the cobalt-free material is nano-scale, and the optional additive chemical formula is LiNi _x3 Co _y3 Mn _1-x3-y3 O ₂ (x 3 is more than or equal to 0.5 and less than 1, y3 is more than 0 and less than or equal to 0.05), optionally addingA small amount of other positive active material is added.

For specific selection of the cobalt-free material and the low-cobalt material, reference may be made to the selection of the cobalt-free material and the low-cobalt material in the first positive electrode active material layer 2312a in the positive electrode sheet, and details are not described here.

The binder can be one or more of styrene butadiene rubber, aqueous acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol and polyvinyl butyral. The conductive agent may be at least one of conductive carbon black, carbon fiber, carbon nanotube, ketjen black, graphene, or acetylene black. The solvent can be one or more of dimethyl glutarate, N-methyl pyrrolidone and deionized water. The first positive electrode active slurry may further include a leveling agent, a dispersant, and the like, which is not limited in the present application.

S120, preparing second positive active slurry: the second positive electrode active material, the binder, and the conductive agent are dispersed in a solvent to form a second positive electrode active slurry. The second positive electrode active material may be the second positive electrode active material described above, for example: the chemical formula is LiFe _x2 Mn _(1-x2) PO ₄ (x 2 is more than 0 and less than 1), the Dv50 of the lithium manganese iron phosphate material is micron-sized, and optionally lithium iron phosphate can be added, and a small amount of other anode active materials can be added.

For specific selection of the lithium iron manganese phosphate material and the lithium iron phosphate material, reference may be made to selection of the lithium iron manganese phosphate material and the lithium iron phosphate material in the second positive electrode active material layer 2312b in the positive electrode sheet, which is not described herein again.

The binder, the conductive agent and the solvent can be the binder, the conductive agent, the solvent and the like in the first positive electrode active slurry, and the binder in the first positive electrode active slurry and the binder in the second positive electrode active material can be the same or different; the conductive agent in the first positive electrode active slurry and the conductive agent in the second positive electrode active material may be the same or different; the solvent in the first positive electrode active paste may be the same as or different from the solvent in the second positive electrode active material. Meanwhile, a leveling agent, a dispersing agent and the like can be added into the second positive electrode active slurry, and the application is not limited.

The first positive electrode active material may also be at least partially surface-coated with a first conductive polymer layer having a structure. And/or, the second positive electrode active material can also be at least partially coated with a second structural conductive polymer layer. The material of the first structure-type conductive polymer layer and the material of the second structure-type conductive polymer layer have been described above and will not be described here.

The manner of coating the first electrically conductive polymer layer is dependent on the material of the first electrically conductive polymer layer. In one embodiment, the method of coating the first structured conductive polymer layer may be: the first positive electrode active material, the first structural conductive polymer, and the solvent are uniformly mixed and then dried. Alternatively, the material of the first conductive polymer layer may be a single conductive polymer material, or may be a composite conductive polymer material (a material in which two or more conductive polymers are mixed). (mass of the first configuration conductive polymer)/(mass of the first configuration conductive polymer + mass of the first positive electrode active material) × 100% =0.5% to 3%.

For example: the material of the first conductive polymer layer with a structure is a mixture of polyaniline and polyethylene glycol, and the method for coating the first conductive polymer layer with a structure can be as follows: stirring a first positive electrode active material, polyaniline, polyethylene glycol and a solvent (such as ethanol) for 4 to 8 hours at the speed of 200 to 500r/min, and then drying for 10 to 15 hours at the temperature of 100 to 150 ℃ to obtain a coated first positive electrode active material; (the mass of polyaniline + the mass of polyethylene glycol)/(the mass of polyaniline + the mass of polyethylene glycol + the mass of the positive electrode active material) × 100% =0.5% -3%.

In another embodiment, the method of coating the first structured conductive polymer layer may be: uniformly mixing a first positive electrode active material, a first structural conductive polymer monomer, an initiator and a solvent, crosslinking the first structural conductive polymer monomer on at least part of the surface of the first positive electrode active material to form a first structural conductive polymer, and drying. Alternatively, the material of the first structured conductive polymer layer may be a single conductive polymer material. (the mass of the first configuration conductive polymer monomer)/(the mass of the first configuration conductive polymer monomer + the mass of the first positive electrode active material) × 100% =0.5% to 3%.

For example: the material of the first conductive polymer layer with a structure of bonding is polyethylene glycol, and the method for coating the first conductive polymer layer with a structure of bonding can be as follows: stirring the first positive electrode active material, ethylene oxide and water for 4-8 h at the speed of 200-500 r/min, hydrolyzing the ethylene oxide on the surface of the positive electrode active material to form polyethylene glycol, and drying for 10-15 h at the temperature of 100-150 ℃ to obtain the coated positive electrode active material. (mass of ethylene oxide)/(mass of ethylene oxide + mass of first positive electrode active material) × 100% =0.5% to 3%.

The coating manner of the second structure type conductive polymer layer may be the same as that of the first structure type conductive polymer layer, except that the coated object is replaced by the second positive electrode active material instead of the first positive electrode active material, and details of the specific coating manner are not described here.

S130, preparing a first positive active material layer 2312a: the first cathode active paste is coated on the surface of the cathode current collector 2311 and then dried to form a first cathode active material layer 2312a. Here, the coating may be performed on one surface or both surfaces of the positive electrode current collector 2311 as needed.

Wherein, the coating mode can be as follows: knife coating, roll coating, slot coating, and the like, without limitation. Step S120 and step S130 may be exchanged or performed simultaneously, and the present application is not limited thereto.

S140, preparing a second positive electrode active material layer 2312b: the second cathode active paste is coated on the surface of the first cathode active material layer 2312a, and then dried to form a second cathode active material layer 2312b. Here, the second cathode active material layer 2312b may be formed on the surface of the first cathode active material layer 2312a according to the condition of the first cathode active material layer 2312a at the time of coating.

In the present application, the ratio of the coating weight of the first positive electrode active material to the coating weight of the second positive electrode active material is (2-8): 8-2. That is, the ratio of the coating weight of the first cathode active material in the first cathode active paste to the coating weight of the second cathode active material in the second cathode active paste is (2-8): (8-2), and after the cathode sheet 231 is prepared, the weight ratio of the first cathode active material in the first cathode active material layer 2312a to the second cathode active material in the second cathode active material layer 2312b is (2-8): (8-2).

As an example, the weight ratio of the first positive electrode active material in the first positive electrode active material layer 2312a to the second positive electrode active material in the second positive electrode active material layer 2312b is 2.

S150, the second positive electrode active material layer 2312b is rolled to obtain the positive electrode sheet 231. Alternatively, the positive electrode sheet 231 may be obtained by performing roll pressing after preparing the first positive electrode active material layer 2312a and then performing roll pressing after preparing the second positive electrode active material layer 2312b; the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b may be sequentially prepared and then rolled to obtain the positive electrode sheet 231, which is not limited in the present application.

After the positive plate 231 is prepared, the first isolation film, the positive plate 231, the second isolation film and the negative plate are sequentially laminated, a wound flat structure is formed after winding, and then hot pressing is performed to obtain a wound electrode assembly 23; alternatively, after the positive electrode sheet 231 is prepared, the positive electrode sheet 231, the separator, the negative electrode sheet, the separator, and so on are sequentially stacked to form the laminated electrode assembly 23.

The electrode assembly 23 may be used to prepare a battery cell 20, and the battery cell 20 may be used to prepare a battery 100 and provide electrical energy to a powered device.

One or more embodiments are described in more detail below with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

Example 1

Preparing a negative plate:

mixing 95wt% of negative active material particle graphite, 2wt% of conductive agent acetylene black, 2wt% of thickening agent sodium carboxymethyl cellulose and 1wt% of binder styrene butadiene rubber, adding a proper amount of deionized water, and fully stirring and mixing to obtain negative active slurry. The negative active slurry was added at 0.2g/1540.25mm ² After the coating amount of (2) is coated on two surfaces of a copper foil with the thickness of 6 mu m, drying, cold pressing and cutting are carried out, thus obtaining the negative plate.

Preparation of the positive electrode sheet 231:

96wt% of LiNi _x1 Mn _(1-x1) O ₂ The cobalt-free material, 2wt% of acetylene black (a new energy source, not less than 99%) as a conductive agent and 2wt% of polyvinylidene fluoride (a bonding agent, not less than 99.5%) as a bonding agent are mixed, and N-methyl pyrrolidone (AR) is used as a solvent, and the mixture is fully stirred and mixed to obtain the first positive electrode active slurry.

96wt% of the compound of the formula LiFe _x2 Mn _(1-x2) PO ₄ The lithium iron manganese phosphate material, 2wt% of acetylene black as a conductive agent and 2wt% of polyvinylidene fluoride as a binder are mixed, N-methyl pyrrolidone is used as a solvent, and the mixture is fully stirred and mixed to obtain second positive electrode active slurry.

The first positive electrode active slurry was added at 0.15g/1540.25mm ² The coating amount of (a) was coated on both surfaces of an aluminum foil having a thickness of 9 μm and then dried to obtain a first positive active paste layer; the second positive electrode active slurry was added at 0.15g/1540.25mm ² The coating amount of (2) is coated on the two first positive electrode active slurry layers and then dried to obtain a second positive electrode active slurry layer. Then, cold pressing and cutting are performed to obtain the positive electrode sheet 231.

Preparation of the electrode assembly 23:

the isolation film is made of PP (polypropylene) and has a thickness of 20 μm. The negative electrode tab, the first separator, the positive electrode tab 231, and the second separator are stacked and then wound to form the electrode assembly 23.

Preparing the battery cell 20:

the electrode assembly 23 is housed in a case, and an electrolyte is injected, followed by vacuum packaging, standing, formation, shaping, and the like, to obtain a battery cell 20.

The parameters of the positive electrode plate 231 are shown in table 1:

TABLE 1 parameters of the Positive electrode plate 231

The performance of the battery cell 20 prepared in the examples and comparative examples was examined:

(1) Capacity test of battery 100

The lithium ion secondary battery 100 was charged at 25 ℃ to 4.3V at a constant current of 1C, further charged at a constant voltage of 4.3V to a current of 0.05C, and then discharged at 0.33C to 2.0V, and the amount of charge discharged this time was taken as the capacity of the electrode assembly 23.

(2) Cycle performance test at 25 deg.C

At 25 ℃, the lithium ion secondary battery 100 is charged to 4.3V with a constant current of 1C, further charged to a current of 0.05C with a constant voltage of 4.3V, and the battery 100 is discharged to 2.0V with a constant current of 1C, which is a charge-discharge cycle process, and the discharge capacity of this time is the discharge capacity of the 1 st cycle. The battery cell 20 is subjected to a plurality of cycle charge and discharge tests in the above manner, the discharge capacity of the 200 th cycle is detected, and the capacity retention rate of the battery 100 after the cycle is calculated by the following formula.

Capacity retention (%) after 100 cycles of the battery = [ discharge capacity at 200 th cycle/discharge capacity at 1 st cycle ] × 100%.

(3) Electrode assembly 23 gas production testing

The lithium ion secondary battery 100 was charged at 25C to 4.3V at a constant current of 1C, further charged at a constant voltage of 4.3V to a current of 0.05C, stored at a temperature increased to 70℃, taken out every 5 days, and the volume of the electrode assembly 23 was measured using a drainage method, with a cutoff condition of 60 days of storage or 30% excess of the volume of the electrode assembly 23.

The performance of the battery cell 20 is shown in table 2:

TABLE 2 Performance of Battery cell 20

As is apparent from the contents of tables 1 and 2, when the particle size of the cobalt-free material is small, the capacity of the obtained electrode assembly 23 is high, and when the particle size of the cobalt-free material is large, the capacity of the obtained electrode assembly 23 is low. If the lithium iron manganese phosphate material layer is not disposed above the cobalt-free material, the capacity of the electrode assembly 23 is high, but the gas yield is high, and the capacity retention rate is low.

From the comparison of R1 to R3, it is found that the larger the amount of the cobalt-free material added, the higher the capacity of the electrode assembly 23; meanwhile, the lower the capacity retention rate, the higher the gas production. From the combinations of R1 to R3 and R12 and R13, it is found that the electrode assembly 23 has a good overall performance when the amount of the cobalt-free material is 30% to 70%.

Meanwhile, as can be seen from the comparison between R1 and R4 to R11, the electrode assembly 23 has better overall performance when the Dv50 of the cobalt-free material is 100nm to 300nm and the Dv50 of the lithium iron manganese phosphate material is 1 μm to 3 μm.

Example 2

R14 to R22 are substantially the same as R1 except that: the selection of the positive electrode active material is varied, and the specific material selection and corresponding performance of the electrode assembly 23 are shown in table 3 (test method as in example 1):

TABLE 3 Positive electrode active Material and Performance of electrode Assembly 23

As can be seen from Table 3, the comparison among R1, R14 and R15 shows that the more the Ni is added into the cobalt-free material, the higher the capacity of the electrode assembly 23 is, the more obvious the gas generation is, and the capacity retention rate is reduced; thus, liNi _x1 Mn _(1-x1) O ₂ In the cobalt-free material (3), x1 is 0.4-0.6, and the performance of the electrode assembly 23 is better.

Comparing R1 and R16-R19, it can be seen that the addition amount of Fe in the lithium iron manganese phosphate material does not substantially affect the capacity of the electrode assembly 23; the more the Fe addition, the higher the capacity retention rate and the less the gas production rate, but the lower the voltage plateau, resulting in lower energy density; thus, liFe _x2 Mn _(1-x2) PO ₄ In the lithium iron manganese phosphate material, x2 is more than or equal to 0.2 and less than or equal to 0.8, and the performance of the electrode assembly 23 is better.

Comparing R1 with R20, it can be seen that the addition of a small amount of low cobalt material to the cobalt-free material does not substantially affect the capacity of the electrode assembly 23, but the capacity retention rate is significantly improved and the gas production is significantly reduced.

When R1 is compared with R21, liFe _0.5 Mn _0.5 PO ₄ A small amount of LiFe is added into the material _0.6 Mn _0.4 PO ₄ The capacity retention ratio of the electrode assembly 23 can be improved while maintaining the energy density thereof, and the gas yield can be reduced.

When R1 is compared with R22, liFe _0.5 Mn _0.5 PO ₄ A small amount of LiFe is added into the material _0.3 Mn _0.7 PO ₄ The capacity retention rate can be ensured, the gas production rate is less, and the energy density can be improved.

Example 3

R23 to R33 are substantially the same as R1 except that: the materials of the structural conductive polymer layer coated on the surface of the positive active material are different, and the preparation method of the positive active material comprises the following steps: dissolving the positive active material and a certain proportion of conductive polymer in ethanol, stirring for 6h at low speed (400 r/min) by using a magnetic stirrer, and then drying for 12h in vacuum at 120 ℃ to obtain the coated positive active material.

The properties of the conductive polymer and the corresponding electrode assembly 23 are shown in table 4 (weight average molecular weight of the aniline and the polyethylene glycol in table 4 is 40000, and the weight average molecular weight of the polyethylene glycol is 2000, and the test method is as in example 1):

TABLE 4 conductive layer on surface of cathode active material and Performance of electrode Assembly 23

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As can be seen from table 4, after the surface of the positive electrode active material layer 2312 is coated with the conductive polymer layer, the capacity of the electrode assembly 23 thereof is increased, the capacity cycle retention rate is also increased, and the gas production is decreased.

Comparison of R23 to R25 shows that increasing the amount of the conductive polymer layer reduces the capacity of the electrode assembly 23 to some extent, but the cycle capacity retention ratio is greatly improved and the gas production is greatly reduced. And comparing with R1, it is known that the addition of a small amount of conductive polymer layer (1% to 3%) increases not only the capacity of the electrode assembly 23 but also the capacity retention rate and the gas production rate, as compared with the case where no conductive polymer layer is added.

As can be seen from comparison between R24 and R26, when the surface of the positive electrode active material layer 2312 is coated with the conductive polymer layer, the addition amount of the cobalt-free material is increased, which not only increases the capacity of the electrode assembly 23, but also increases the capacity retention rate of the electrode assembly 23, and reduces the gas yield of the electrode assembly 23.

Comparing R24 with R27, R28, and R31 to R33, it can be seen that the capacity retention rate of the electrode assembly 23 is higher and the gas yield is lower compared to the case where the surface of the cobalt-free material is coated with only the aniline or the polyethylene glycol, and the surface of the cobalt-free material is coated with the mixture of the aniline and the polyethylene glycol. As can be seen from comparison of R24 with R29 and R30, the surface of the lithium iron manganese phosphate material is only coated with the isoaniline or the polyethylene glycol, or the surface of the lithium iron manganese phosphate material is coated with the mixture of the isoaniline and the polyethylene glycol, which has little influence on the performance of the electrode assembly 23.

The embodiments described above are some, but not all embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.

Claims

1. The utility model provides a positive plate, its characterized in that, includes anodal mass flow body and anodal active material layer, anodal active material layer including cover in first anodal active material layer and the anodal active material layer of second that the surface of anodal mass flow body outwards set gradually, first anodal active material in the first anodal active material layer includes that the chemical formula is LiNi _x1 Mn _(1-x1) O ₂ The x1 is more than 0 and less than 1; the second positive active material in the second positive active material layer comprises LiFe with a chemical formula _x2 Mn _(1-x2) PO ₄ X2 is more than 0 and less than 1; the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micrometer level.

2. The positive electrode sheet according to claim 1, wherein the Dv50 of the cobalt-free material is 100nm to 300nm, and the Dv50 of the lithium iron manganese phosphate material is 1 μm to 3 μm.

3. The positive electrode sheet according to claim 1, wherein the cobalt-free material is present in the first positive electrode active material and the second positive electrode active material at a ratio of 20% to 80% by mass.

4. The positive electrode sheet according to claim 1, wherein the first positive electrode active material further comprises LiNi _x3 Co _y3 Mn _1-x3-y3 O ₂ Wherein x3 is more than or equal to 0.5 and less than 1, y3 is more than 0 and less than or equal to 0.05, and the mass ratio of the low cobalt material in the first positive electrode active material is not more than 30%.

5. The positive electrode sheet according to claim 2, wherein the absolute value of the difference between the voltage plateau of the first positive electrode active material and the voltage plateau of the second positive electrode active material is 0.3V or less.

6. The positive electrode sheet according to claim 5, wherein x2 is 0.2. Ltoreq. X2. Ltoreq.0.8.

7. The positive electrode sheet according to claim 6, wherein the second positive electrode active material comprises a material having a chemical formula of LiFe _0.5 Mn _0.5 PO ₄ And the chemical formula is LiFe _0.3 Mn _0.7 PO ₄ The lithium iron manganese phosphate material of (1), the LiFe _0.3 Mn _0.7 PO ₄ The mass ratio of the material in the second positive electrode active material is not higher than 30%.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein at least a part of the surface of the first positive electrode active material is coated with a first configuration-conductive polymer layer, and the mass of the first configuration-conductive polymer layer is 0.5% to 3% of the total mass of the first positive electrode active material and the first configuration-conductive polymer layer;

and/or at least part of the surface of the second positive electrode active material is coated with a second structure type conductive polymer layer, and the mass of the second structure type conductive polymer layer accounts for 0.5-3% of the total mass of the second positive electrode active material and the second structure type conductive polymer layer.

9. The positive electrode sheet according to claim 8, wherein the material of the first structure-type conductive polymer layer and/or the material of the second structure-type conductive polymer layer includes an ionic polymer and an electronic polymer.

10. The positive electrode sheet according to claim 9, wherein the ionic polymer comprises at least one of polyethylene glycol, polyethylene oxide, polyethylene glycol succinate, polyethylene glycol imine;

the electronic polymer comprises at least one of polyaniline, polythiophene, polypyrrole and polyquinoline.

11. The positive electrode sheet according to claim 9, wherein the material of the first structure-type conductive polymer layer and/or the material of the second structure-type conductive polymer layer is a mixture of polyaniline and polyethylene glycol, and the polyaniline accounts for 30% to 70% by mass of the mixture.

12. The positive electrode sheet according to claim 11, wherein the weight average molecular weight of the polyaniline is 20000 to 80000, and the structural formula of the polyaniline is:

wherein y =0.5./>

13. The positive electrode sheet according to claim 11, wherein the polyethylene glycol has a weight average molecular weight of 800 to 4000.

14. An electrode assembly comprising a negative electrode sheet, a separator and the positive electrode sheet according to any one of claims 1 to 13, the separator being disposed between the positive electrode sheet and the negative electrode sheet.

15. A battery cell comprising the electrode assembly of claim 14.

16. A battery comprising the cell of claim 15.

17. An electrical device comprising the battery of claim 16.

18. The preparation method of the positive plate is characterized by comprising the following steps:

coating the first positive electrode active slurry on the surface of a positive electrode current collector to form a first positive electrode active material layer, wherein the first positive electrode active material in the first positive electrode active slurry comprises LiNi (lithium iron oxide) with a chemical formula _x1 Mn _(1-x1) O ₂ The x1 is more than 0 and less than 1;

coating a second positive electrode active slurry on the surface of the first positive electrode active material layer to form a second positive electrode active material layer, wherein the second positive electrode active material in the second positive electrode active slurry comprises LiFe with a chemical formula _x2 Mn _(1-x2) PO ₄ X2 is more than 0 and less than 1;

the Dv50 of the cobalt-free material is in a nanometer level, and the Dv50 of the lithium iron manganese phosphate material is in a micrometer level.

19. The production method according to claim 18, wherein a ratio of the coating weight of the first positive electrode active material to the coating weight of the second positive electrode active material is (2-8) to (8-2).

20. The production method according to claim 18, characterized by further comprising, before the application of the first positive electrode active slurry, a step of coating at least a part of a surface of the first positive electrode active material with a first conductive polymer layer of a bonding configuration;

and/or, before coating the second positive electrode active slurry, coating a second structure type conductive polymer layer on at least part of the surface of the second positive electrode active material.

21. The method of producing as claimed in claim 20 wherein the method of coating the first structured conductive polymer layer comprises: uniformly mixing the first positive electrode active material, the first structural conductive polymer and a solvent, and then drying;

and/or, a method of coating the second structured conductive polymer layer, comprising: and uniformly mixing the second positive electrode active material, the second structure type conductive polymer and the solvent, and then drying.

22. The method of producing as claimed in claim 20 wherein the method of coating the first structured conductive polymer layer comprises: uniformly mixing the first positive electrode active material, a first configuration conductive polymer monomer, an initiator and a solvent, crosslinking the first configuration conductive polymer monomer on at least part of the surface of the first positive electrode active material to form a first configuration conductive polymer, and then drying;

and/or, a method of coating the second structured conductive polymer layer, comprising: and uniformly mixing the second positive electrode active material, a second structure type conductive polymer monomer, an initiator and a solvent, crosslinking the second structure type conductive polymer monomer on at least part of the surface of the second positive electrode active material to form a second structure type conductive polymer, and drying.