CN117117086B

CN117117086B - Positive plate, battery monomer, battery and power utilization device

Info

Publication number: CN117117086B
Application number: CN202311379609.XA
Authority: CN
Inventors: 吴凯; 潘坚福; 尚义博; 秦一鸣; 裴人杰; 徐晓富; 何建福; 叶永煌
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2023-10-24
Filing date: 2023-10-24
Publication date: 2024-03-29
Anticipated expiration: 2043-10-24
Also published as: CN117117086A

Abstract

A positive plate, a battery monomer, a battery and an electricity utilization device, belonging to the technical field of batteries; the positive electrode sheet includes a positive electrode active material layer including a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer including a first positive electrode active material, the second positive electrode active material layer including a second positive electrode active material, the lattice shrinkage rate a of the first positive electrode active material being greater than the lattice shrinkage rate b of the second positive electrode active material, the relationship of the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer being controlled to satisfy: c is less than or equal to 0.014/(a-b), so as to reduce the occurrence of ion bridge cutoff of the first positive electrode active material layer and the second positive electrode active material layer, and further improve the electrical property of the whole positive electrode plate.

Description

Positive plate, battery monomer, battery and power utilization device

Technical Field

The application relates to the technical field of batteries, in particular to a positive plate, a battery cell, a battery and an electric device.

Background

In the positive electrode sheet in which a plurality of positive electrode active materials are used in combination, in order to reduce the occurrence of ion transmission bridge cutoff caused by the difference in volume expansion of each positive electrode active material and the possibility of occurrence of current non-uniformity among each positive electrode active material, each positive electrode active material is generally layered, however, the positive electrode sheet after layered arrangement still has the problem of poor electrical performance.

Disclosure of Invention

In view of the above, the present application provides a positive electrode sheet, a battery cell, a battery, and an electrical device, which can reduce the occurrence of ion bridge cutoff, thereby improving electrical performance.

In a first aspect, the present application provides a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material layer and a second positive electrode active material layer, the first positive electrode active material layer includes a first positive electrode active material, the second positive electrode active material layer includes a second positive electrode active material, lattice shrinkage a of the first positive electrode active material is greater than lattice shrinkage b of the second positive electrode active material, a relationship between lattice shrinkage a of the first positive electrode active material, lattice shrinkage b of the second positive electrode active material, and a ratio c of a thickness of the first positive electrode active material layer to a thickness of the positive electrode active material layer satisfies: c is less than or equal to 0.014/(a-b).

In the technical scheme of the embodiment of the application, by controlling the relation among the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer, the following conditions are satisfied: c is less than or equal to 0.014/(a-b), so as to reduce the occurrence of ion bridge cutoff of the first positive electrode active material layer and the second positive electrode active material layer, and further improve the electrical property of the whole positive electrode plate. Meanwhile, the first positive electrode active material and the second positive electrode active material are arranged in a layered mode, the possibility of current non-uniformity phenomenon between the first positive electrode active material and the second positive electrode active material can be reduced, and further the positive electrode plate has higher capacity retention rate in the earlier period of circulation.

In some embodiments, the relationship of the lattice shrinkage a of the first positive electrode active material, the lattice shrinkage b of the second positive electrode active material, and the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: c is less than or equal to 0.01/(a-b).

In the above-described implementation, the relationship among the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer is controlled to satisfy: c is less than or equal to 0.01/(a-b), the occurrence of ion bridge cutoff of the first positive electrode active material layer and the second positive electrode active material layer can be further reduced, and the electrical performance of the whole positive electrode plate is further improved.

In some embodiments, the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: 80 percent or more and 20 percent or more of c.

In the implementation process, when the usage ratio of the two positive electrode active materials is large, the difference of the electrical properties of the formed positive electrode sheet is not large no matter what type of matched use mode is adopted for the two positive electrode active materials. When the difference of the usage amounts of the two positive electrode active materials is smaller, the two positive electrode active materials adopt a layered matching mode, and the relationship among the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer is matched and controlled to meet the following conditions: c is less than or equal to 0.014/(a-b), and the formed positive plate has better electrical property. In the layering setting process of the using amounts of the two positive electrode active materials, the thickness of the first positive electrode active material layer accounts for 20% -80% of the thickness of the positive electrode active material layer, and the relationship that c is less than or equal to 0.014/(a-b) is satisfied by controlling the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer, so that the obtained positive electrode sheet has obviously better electrical performance.

In some embodiments, the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: 70 percent or more and 30 percent or more of c.

In the implementation process, the use amount of the two positive electrode active materials is layered to meet the requirement that the thickness of the first positive electrode active material layer accounts for 30% -70% of the thickness of the positive electrode active material layer, and the relationship that c is less than or equal to 0.014/(a-b) is met by controlling the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer, so that the electric performance of the positive electrode plate has more obvious advantages.

In some embodiments, the first positive electrode active material has a lattice shrinkage a of 6.2% -6.8%; and/or

The lattice shrinkage b of the second positive electrode active material is 2.5% -4.5%.

In some embodiments, the first positive electrode active material comprises a polyanionic positive electrode material; and/or

The second positive electrode active material includes a ternary system material.

In the implementation process, the polyanion positive electrode material generally shows better safety performance, the ternary system material generally shows higher energy density, and the polyanion positive electrode material is adopted as the second positive electrode active material, and the ternary system material is adopted as the first positive electrode active material, so that the positive electrode sheet has higher safety performance and higher energy density.

In some embodiments, the polyanionic positive electrode material includes LiMPO ₄ M comprises Mn and non-Mn elements, the non-Mn elements comprise one or two of a first doping element and a second doping element, the first doping element is doped with manganese, and the second doping element is doped with phosphorus.

Optionally, the first doping element comprises one or more of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge.

Optionally, the second doping element includes one or more of B, S, si and N.

Alternatively, the polyanionic positive electrode material includes Li _1+x Mn _1-y A _y P _1-z R _z O ₄ Wherein x is any number in the range of-0.100 to 0.100, y is any number in the range of 0.001 to 0.500, z is any number in the range of 0.001 to 0.100, A comprises one or more elements of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge, and R comprises one or more elements of B, S, si and N.

Alternatively, the polyanionic positive electrode material includes Li _h A _i Mn _1-j B _j P _1-k C _k O _4-l D _l Wherein a comprises one or more of Zn, al, na, K, mg, nb, mo and W; b comprises one or more elements of Ti, V, zr, fe, ni, mg, co, ga, sn, sb, nb and Ge; c comprises one or more elements of B, S, si and N; d comprises one or more elements of S, F, cl and Br; h is selected from the range of 0.9 to 1.1, i is selected from the range of 0.001 to 0.1, j is selected from the range of 0.001 to 0.5, k is selected from the range of 0.001 to 0.1, l is selected from the range of 0.001 to 0.1, and the polyanionic positive electrode material is electrically neutral.

In some embodiments, the polyanionic positive electrode material also has a coating layer comprising carbon.

In the above-described implementation, the introduction of the carbonaceous coating layer improves the conductivity of the positive electrode active material. At this time, the structure of the positive electrode active material is actually LiMPO ₄ The core-shell structure is a core, and the surface of the core is coated with a coating layer.

In some embodiments, the ternary system material includes a nickel cobalt manganese ternary material and modifications thereof and a nickel cobalt aluminum ternary material and modifications thereof.

In the implementation process, the modified material of the nickel-cobalt-manganese ternary material and the modified material of the nickel-cobalt-aluminum ternary material refer to materials obtained by doping or cladding the nickel-cobalt-manganese ternary material or the nickel-cobalt-aluminum ternary material respectively.

In some embodiments, the ternary system material includes Li _a Ni _b Co _c M1 _d M2 _e O _f R _g Wherein a is more than or equal to 0.75 and less than or equal to 1.2,0<b<1，0<c<1，0<d<E is more than or equal to 1 and less than or equal to 0.2,1, f is more than or equal to 0 and less than or equal to 2.5, g is more than or equal to 0 and less than or equal to 1, f+g is more than or equal to 3, M1 is one or two elements selected from Mn or Al, M2 is one or more elements selected from Zr, zn, cu, cr, mg, fe, V, ti, sr, sb, Y, W, nb, and R is one or more elements selected from N, F, S, cl.

In a second aspect, the present application provides a positive electrode sheet including a positive electrode active material layer including a first positive electrode active material and a second positive electrode active material layer including a second positive electrode active material, the first positive electrode active material layer having a lattice shrinkage a greater than a lattice shrinkage b of the second positive electrode active material, the first positive electrode active material including LiMPO ₄ The M comprises Mn and non-Mn elements, the non-Mn elements comprise one or two of a first doping element and a second doping element, the first doping element is doped with manganese, the second doping element is doped with phosphorus, the second positive electrode active material comprises a ternary system material, and the relation among the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer is as follows: c is less than or equal to 0.014/(a-b).

In the technical solution of the embodiment of the application, by controlling LiMPO ₄ The relationship of the lattice shrinkage a of the ternary system material, the lattice shrinkage b of the ternary system material, and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer satisfies: c is less than or equal to 0.014/(a-b), so as to reduce the occurrence of ion bridge cutoff of the first positive electrode active material layer and the second positive electrode active material layer, and further improve the electrical property of the whole positive electrode plate. At the same time, the ternary system material and LiMPO ₄ Layered arrangement can reduce ternary system materials and LiMPO ₄ The possibility of current non-uniformity phenomenon occurs between the two, so that the positive plate has higher capacity retention rate in the earlier cycle period. In addition, liMPO ₄ Generally shows better safety performance, the ternary system material generally shows higher energy density, and LiMPO is adopted ₄ As the second positive electrode active material, the ternary system material as the first positive electrode active material can enableThe positive plate has higher safety performance and higher energy density.

In a third aspect, the present application provides a battery cell comprising the positive electrode sheet provided in the first aspect or the second aspect.

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

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

Drawings

Various other 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. Also, like reference numerals are used to designate like parts throughout the accompanying drawings. In the drawings:

FIG. 1 is a schematic illustration of a vehicle according to some embodiments of the present application;

Fig. 2 is a schematic exploded view of a secondary battery according to some embodiments of the present application;

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 some embodiments of the present application;

fig. 5 is a first schematic structural view of a positive plate according to some embodiments of the present disclosure;

fig. 6 is a second schematic structural view of a positive plate according to some embodiments of the present disclosure;

fig. 7 is a flowchart of a method for preparing a positive electrode sheet according to some embodiments of the present application.

Reference numerals in the specific embodiments are as follows:

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

Detailed Description

Embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical solutions of the present application, and thus are only examples, and are not intended to limit the scope of protection of the present application.

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 "comprising" and "having" and any variations thereof in the description and claims of the present application and in the description of the figures above are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first," "second," etc. are used merely to distinguish between different objects and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated, a particular order or a primary or secondary relationship. In the description of the embodiments of the present application, the meaning of "plurality" is two or more unless explicitly defined otherwise.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearances of such phrases 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. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is merely an association relationship describing an association object, which means that three relationships may exist, for example, a and/or B may mean: a exists alone, A and B exist together, and B exists alone. In addition, the character "/" herein generally indicates that the front and rear associated objects are 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), and "plural sheets" refers to two or more (including two).

In the description of the embodiments of the present application, the orientation or positional relationship indicated by the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. are based on the orientation or positional relationship shown in the drawings, and are merely for convenience of describing the embodiments of the present application and for simplifying the description, rather than indicating or implying that the apparatus or element referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the embodiments of the present application.

In the description of the embodiments of the present application, unless explicitly specified and limited otherwise, the terms "mounted," "connected," "secured" and the like are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally formed; or may be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the embodiments of the present application will be understood by those of ordinary skill in the art according to the specific circumstances.

Currently, the application of power batteries is more widespread from the development of market situation. 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, aerospace, and the like. With the continuous expansion of the application field of the power battery, the market demand of the power battery is also continuously expanding.

The power battery can be a lithium ion battery, and the lithium ion battery has very wide application in the fields of portable electronic equipment, electric automobiles and the like. In the process of manufacturing electrode plates of lithium ion secondary batteries, a single-layer coating is generally adopted, a required active material is coated on a current collector in a single layer, and along with the increase of requirements on energy density and safety performance, it has been proposed to combine a positive active material with high energy density characteristics, such as a ternary system material, with a positive active material with high safety performance characteristics, such as a polyanion positive material, to achieve both energy density and safety performance.

However, when a positive electrode active material having a high energy density characteristic and a positive electrode active material having a high safety performance characteristic are simultaneously incorporated directly in one positive electrode active material layer, a phenomenon in which ion transport bridge cutoff and current non-uniformity occur easily between two positive electrode active materials in the positive electrode active material layer due to a difference in volume expansion, which affects the electrical performance of the positive electrode sheet when the difference in the amounts of the two positive electrode active materials is small, occurs.

In order to reduce the influence on the electrical property of the positive plate, two active materials can be arranged in a layered manner, however, after the layered arrangement, the influence on the electrical property of the positive plate caused by ion bridge cutoff is still larger.

Based on the above consideration, to reduce the influence of ion bridge cutoff on the electrical performance of the positive plate, the electrical performance of the positive plate is improved. The application provides a positive plate, positive plate includes positive electrode active material layer, positive electrode active material layer includes first positive electrode active material layer and second positive electrode active material layer, first positive electrode active material layer includes first positive electrode active material, second positive electrode active material layer includes second positive electrode active material, lattice contraction rate a of first positive electrode active material is greater than lattice contraction rate b of second positive electrode active material, the relation of lattice contraction rate a of first positive electrode active material, lattice contraction rate b of second positive electrode active material and the proportion c of positive electrode active material layer thickness occupy positive electrode active material layer thickness satisfies: c is less than or equal to 0.014/(a-b).

In such a positive electrode sheet, by controlling the relationship of the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness, it is satisfied that: c is less than or equal to 0.014/(a-b), so as to reduce the occurrence of ion bridge cutoff of the first positive electrode active material layer and the second positive electrode active material layer, and further improve the electrical property of the whole positive electrode plate. Meanwhile, the first positive electrode active material and the second positive electrode active material are arranged in a layered mode, the possibility of current non-uniformity phenomenon between the first positive electrode active material and the second positive electrode active material can be reduced, and further the positive electrode plate has higher capacity retention rate in the earlier period of circulation.

The positive electrode sheet can be used to prepare an electrode assembly that can be used, but is not limited to, in electrical devices such as vehicles, boats, or aircraft. A power supply system having a battery cell, a secondary battery, or the like disclosed in the present application, which constitutes the power consumption device, may be used.

The embodiment of the application provides an electricity utilization device using a battery as a power supply, wherein the electricity utilization device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft and the like. Among them, the electric toy may include fixed or mobile electric toys, such as game machines, electric car toys, electric ship toys, electric plane toys, and the like, and the spacecraft may include planes, rockets, space planes, and spacecraft, and the like.

For convenience of description, the following embodiment will take an electric device according to an embodiment of the present application as an example of the vehicle 1000.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a vehicle 1000 according to some embodiments of the present application. The vehicle 1000 may be a fuel oil vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or a range-extended vehicle. The vehicle 1000 is provided with a secondary battery 100 inside, and the secondary battery 100 may be provided at the bottom or at the head or at the tail of the vehicle 1000. The secondary battery 100 may be used for power supply of the vehicle 1000, for example, the secondary battery 100 may serve as an operating power source of the vehicle 1000. The vehicle 1000 may further include a controller 300 and a motor 200, the controller 300 being configured to control the secondary battery 100 to supply power to the motor 200, for example, for operating power requirements during start-up, navigation, and travel of the vehicle 1000.

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

In this application, the secondary battery 100 may refer to a single battery cell 20, which may also refer to a single physical module including a plurality of battery cells 20 to provide higher voltage and capacity, which may be in the form of a battery pack, a battery module, or the like. The secondary battery 100 may include a case 10 to house a plurality of battery cells 20, and the case 10 may prevent liquid or other foreign matter from affecting the charge or discharge of the battery cells 20.

Fig. 2 is a schematic exploded structure view of a secondary battery 100 according to some embodiments of the present application. Referring to fig. 2, the secondary 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 an accommodating space 11 for the battery cells 20. In some embodiments, the case 10 may include a first portion 12 and a second portion 13, the first portion 12 and the second portion 13 being overlapped with each other to define a receiving space 11 for receiving the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealing member (not shown), which may be a sealing ring, a sealant, or the like.

The first portion 12 and the second portion 13 may be of various shapes, such as a rectangular parallelepiped, a cylinder, etc. The first part 12 may be a hollow structure having one side opened to form a receiving cavity for receiving the battery cell 20, and the second part 13 may be a hollow structure having one side opened to form a receiving cavity for receiving the battery cell 20, and the opening side of the second part 13 is closed to the opening side of the first part 12, thereby forming the case 10 having the receiving space 11. Of course, as shown in fig. 2, the first portion 12 may be a hollow structure with one side opened, the second portion 13 may be a plate-like structure, and the second portion 13 may be covered on the opening side of the first portion 12, thereby forming the case 10 having the accommodation space 11.

In the secondary battery 100, a plurality of battery cells 20 may be connected in series, parallel, or a series-parallel connection between the plurality of battery cells 20, and the series-parallel connection means that the plurality of battery cells 20 are connected in both series and parallel. The plurality of battery cells 20 can be directly connected in series or in parallel or in series-parallel, and then the whole formed by the plurality of battery cells 20 is accommodated in the box 10; of course, a plurality of battery cells 20 may be connected in series or parallel or series-parallel to form a battery module, and then connected in series or parallel or series-parallel to form a whole and be accommodated in the case 10. The battery cell 20 may be in the shape of a cylinder, a flat body, a rectangular parallelepiped, or other shapes, etc. Fig. 2 exemplarily shows a case in which the battery cell 20 has a square shape.

In some embodiments, the secondary battery 100 may further include a bus bar part (not shown), through which electrical connection between the plurality of battery cells 20 may be achieved, to achieve series connection or parallel connection or series-parallel connection of the plurality of battery cells 20.

Fig. 3 is a schematic structural diagram of a battery cell 20 according to some embodiments of the present application, and fig. 4 is an exploded view of the battery cell 20 according to some embodiments of the present application. 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 where the case 21 and the electrode assembly 23 are square.

The material of the housing 21 may be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., which is not particularly limited in the embodiment of the present application.

The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The cap assembly 22 serves to cover the opening 211 of the case 21 to form a closed installation space (not shown) for accommodating the electrode assembly 23. The installation space is also used for accommodating an electrolyte, such as an electrolyte solution. The end cap assembly 22 is used as a component for outputting the electric power of the electrode assembly 23, and the electrode terminal 222 in the end cap assembly 22 is used to be electrically connected with the electrode assembly 23, i.e., the electrode terminal 222 is electrically connected with the tab of the electrode assembly 23, for example, the electrode terminal 222 is connected with the tab through the current collecting member 24, so as to achieve the electrical connection of the electrode terminal 222 with the tab.

The number of the openings 211 of the housing 21 may be one or two. If the opening 211 of the housing 21 is one, the end cap assembly 22 may also be one, and two electrode terminals 222 may be disposed in the end cap assembly 22, where 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 the number of the openings 211 of the housing 21 is two, for example, two openings 211 are disposed on two opposite sides of the housing 21, the number of the end cap assemblies 22 may be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the housing 21. In this case, the electrode terminal 222 in one of the end cap assemblies 22 may be a positive electrode terminal for electrical connection with the positive 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 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 the electrode assembly 23 from the case 21. Illustratively, the insulating protector 25 is an adhesive tape adhered to the outer circumference of the electrode assembly 23. In some embodiments, the number of the electrode assemblies 23 is plural, the insulating protection member 25 is disposed around the outer circumferences of the plurality of electrode assemblies 23, and the plurality of electrode assemblies 23 are formed into a unitary structure to keep the electrode assemblies 23 structurally stable.

The electrode assembly 23 includes a positive electrode sheet 231, a negative electrode sheet, and a separator. The positive electrode tab 231 includes a positive electrode current collector 2311 and a positive electrode active material layer 2312, the positive electrode active material layer 2312 is coated on the surface of the positive electrode current collector 2311, the positive electrode current collector 2311 without the positive electrode active material layer 2312 protrudes from the positive electrode current collector 2311 with the positive electrode active material layer 2312 coated, and the positive electrode current collector 2311 without the positive electrode active material layer 2312 serves as a positive electrode tab.

The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer is coated on the surface of the negative electrode current collector, the negative electrode current collector without the negative electrode active material layer protrudes out of the negative electrode current collector coated with the negative electrode active material layer, and the negative electrode current collector without the negative electrode active material layer is used as a negative electrode tab. The material of the negative electrode current collector may be copper, and the negative electrode active material may be carbon, silicon, or the like. In order to ensure that the high current is passed without fusing, the number of positive electrode lugs is multiple and stacked together, and the number of negative electrode lugs is multiple and stacked together. The material of the separator may be PP (polypropylene) or PE (polyethylene). In addition, the electrode assembly 23 may be a wound electrode assembly or a laminated electrode assembly, and the embodiment is not limited thereto.

Fig. 5 is a first schematic structural view of a positive electrode tab 231 provided in some embodiments of the present application, and fig. 6 is a second schematic structural view of a positive electrode tab 231 provided in some embodiments of the present application; referring to fig. 5 and 6, the embodiment of the present application provides a positive electrode sheet 231, the positive electrode sheet 231 includes a positive electrode active material layer 2312, the positive electrode active material layer 2312 includes a first positive electrode active material layer 2312a and a second positive electrode active material layer 2312b, the first positive electrode active material layer 2312a includes a first positive electrode active material, the second positive electrode active material layer 2312b includes a second positive electrode active material, the lattice shrinkage a of the first positive electrode active material is greater than the lattice shrinkage b of the second positive electrode active material, and the relationship among the lattice shrinkage a of the first positive electrode active material, the lattice shrinkage b of the second positive electrode active material, and the thickness c of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 is: c is less than or equal to 0.014/(a-b).

The positive electrode active material layer 2312 is attached to at least a portion of the surface of the positive electrode current collector 2311, and the first positive electrode active material layer 2312a and the second active material layer in the positive electrode active material layer 2312 may be in direct contact with the positive electrode current collector 2311, in other words, the positional relationship of the first positive electrode active material layer 2312a, the second active material layer and the positive electrode current collector 2311 may be: the first positive electrode active material layer 2312a is attached to the positive electrode current collector 2311, and the second positive electrode active material layer 2312b is attached to a surface of the first positive electrode active material layer 2312a facing away from the positive electrode current collector 2311; it may also be: the second positive electrode active material layer 2312b is attached to the positive electrode current collector 2311, and the first positive electrode active material layer 2312a is attached to a surface of the second positive electrode active material layer 2312b facing away from the positive electrode current collector 2311.

The material of the positive electrode 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 electrode active material layer 2312a and a second positive electrode active material layer 2312b are sequentially disposed on one surface of the positive electrode current collector 2311; with continued reference to fig. 6, in another embodiment, a first positive electrode active material layer 2312a and a second positive electrode active material layer 2312b are sequentially disposed on both surfaces of the positive electrode current collector 2311. It should be noted that this is only an illustration that the present embodiment can be implemented, and in other embodiments, the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b may be exchanged.

For a lithium ion battery, the first and second positive electrode active materials in the first and second positive electrode active material layers 2312a and 2312b refer to substances capable of inserting and extracting lithium ions.

The lattice shrinkage of the positive electrode active material means the volume ratio of the volume difference between the initial state and the full-charge state of the positive electrode material to the initial state. The test method comprises the following steps: and (3) independently preparing the positive electrode active material into a soft-package laminated battery, charging to 4.3V according to 0.5C under the constant temperature environment of 25 ℃ and 2.5-4.3V, then charging to the current of less than or equal to 0.05C under the constant voltage of 4.3V, then disassembling the battery to take out a positive electrode plate, performing XRD test, and finishing by XRD data and RietVeld software to obtain the values of a and C axes (material unit cell parameters) required by calculating the unit cell volume of the positive electrode active material under the full charge state, wherein the V full charge = a 2 x C x sin120 DEG, and obtaining V initial by adopting the same process to confirm the condition of the initial positive electrode active material, wherein the lattice volume shrinkage rate= (V initial-V full charge)/V initial. When the lattice shrinkage rate of the positive electrode material of the positive electrode sheet 231 is determined, the thickness of each positive electrode material active layer can be obtained through an electron microscope image, the positive electrode active material layer 2312 to be tested is peeled off according to the thickness information, then the positive electrode active material is soaked in a solvent NMP, the binder in the positive electrode active material is washed out, the positive electrode active material to be tested is obtained, and then the lattice shrinkage rate of the positive electrode active material to be tested is determined by adopting the method.

By controlling the relationship of the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312, it is satisfied that: c is less than or equal to 0.014/(a-b), to reduce the occurrence of ion bridging of the first and second positive electrode active material layers 2312a and 2312b, thereby improving the electrical properties of the entire positive electrode sheet 231. Meanwhile, the first positive electrode active material and the second positive electrode active material are arranged in a layered manner, so that the possibility of current non-uniformity phenomenon between the first positive electrode active material and the second positive electrode active material can be reduced, and the positive electrode sheet 231 has higher capacity retention rate in the early period of circulation.

In the technical solutions of some embodiments of the present application, the relationship among the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 is as follows: c is less than or equal to 0.01/(a-b). By controlling the relationship of the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312, it is satisfied that: c is less than or equal to 0.01/(a-b), the occurrence of ion bridge cutoff of the first and second positive electrode active material layers 2312a and 2312b can be further reduced, so that the electrical performance of the entire positive electrode sheet 231 is further improved.

In some embodiments of the present application, the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 is as follows: 80 percent or more and 20 percent or more of c. When the amounts of the two positive electrode active materials are greatly different, the difference in the electrical properties of the positive electrode tab 231 formed is not great regardless of the manner of the two positive electrode active materials used in combination. When the difference of the usage amounts of the two positive electrode active materials is small, the relationship between the lattice shrinkage a of the first positive electrode active material, the lattice shrinkage b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 is controlled by adopting a layered matching mode, and the relationship is as follows: c is less than or equal to 0.014/(a-b), and the formed positive plate 231 has better electrical performance. In the layering setting process of the two kinds of positive electrode active materials, the thickness of the first positive electrode active material layer 2312a is 20% -80% of the thickness of the positive electrode active material layer 2312, and the relationship of c less than or equal to 0.014/(a-b) is satisfied by controlling the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312, so that the obtained positive electrode sheet 231 has obviously better electrical performance.

Alternatively, the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 satisfies: 70 percent or more and 30 percent or more of c. The use amount of the two positive electrode active materials in the layering setting process satisfies that the thickness of the first positive electrode active material layer 2312a accounts for 30% -70% of the thickness of the positive electrode active material layer 2312, and the relationship that c is less than or equal to 0.014/(a-b) is satisfied by controlling the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312, so that the electric performance of the positive electrode sheet 231 has more obvious advantages.

For example, the ratio of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., and may be any value ranging from 20% to 80%.

In the technical solutions of some embodiments of the present application, the lattice shrinkage a of the first positive electrode active material is 6.2% -6.8%; the lattice shrinkage b of the second positive electrode active material is 2.5% -4.5%.

Illustratively, the lattice shrinkage a of the first positive electrode active material may be 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, or 6.8%, etc., which may also be any value in the range of 6.2% -6.8%. The lattice shrinkage b of the second positive electrode active material may be 2.5%, 2.7%, 2.9%, 3.1%, 3.3%, 3.5%, 3.7%, 3.9%, 4.1%, 4.3%, 4.5%, etc., and may be any value within a range of 2.5% -4.5%.

In some embodiments of the present disclosure, the first positive electrode active material comprises a polyanionic positive electrode material; the second positive electrode active material includes a ternary system material.

The polyanion positive electrode material is a generic name of a series of compounds containing tetrahedral or octahedral anion structural units (XOm) n-, and has the advantages of high charge and discharge voltage, large energy storage capacity, good rapid charge and discharge capacity, good cycle stability and the like, and the synthesis method mainly comprises the following steps: high temperature solid phase method, sol-gel method, hydrothermal method, electrostatic spinning method, etc.

Ternary system materials generally include both the NCA and NCM types. Among them, NCA is widely used because of its long life, large capacity, high energy density, etc., but its specific heat capacity is relatively low; the NCM integrates the advantages of three positive electrode materials, namely lithium cobaltate, lithium nickelate and lithium manganate, and has obvious ternary synergistic effect. NCM can be generally expressed as: liNi _x Co _y Mn _z O ₂ 。

The polyanion positive electrode material generally shows better safety performance, the ternary system material generally shows higher energy density, and the adoption of the polyanion positive electrode material as the second positive electrode active material and the ternary system material as the first positive electrode active material can enable the positive electrode sheet 231 to have higher safety performance and higher energy density.

In some embodiments of the present disclosure, the first positive electrode active material comprises a polyanionic positive electrode material, optionally a polyanionic positive electrode material comprising LiMPO ₄ M includes Mn and non-Mn elements.

The above LiMPO ₄ Not a specific molecular structural formula, is a generalized expression of lithium manganese-containing phosphates.

In some embodiments of the present application, the non-Mn element includes one or two of a first doping element and a second doping element, where the first doping element is doped with manganese, and the second doping element is doped with phosphorus.

In some embodiments of the present application, the first doping element includes one or more elements of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge.

In some embodiments of the present application, the first doping element includes at least two of Fe, ti, V, ni, co and Mg.

In some embodiments of the present application, the second doping element includes one or more elements of B, S, si and N.

In some embodiments of the present application, the second positive electrode active material includes Li _1+x Mn _1-y A _y P _1-z R _z O ₄ ，Li _1+x Mn _1-y A _y P _1-z R _z O ₄ Wherein x is any value in the range of-0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A comprises one or more elements of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge, and R comprises one or more elements of B, S, si and N.

In the technical proposal of some embodiments of the application, the compound Li _1+x Mn _1-y AyP _1-z RzO ₄ The preparation method of (2) can comprise the following steps:

(1) Dissolving a manganese source, a manganese site doped element A source and acid in a solvent and stirring to generate a suspension of manganese salt doped with the element A, filtering the suspension, and drying a filter cake to obtain the manganese salt doped with the element A;

(2) Adding a lithium source, a phosphorus source, an element R source, a solvent and the manganese salt doped with the element A obtained in the step (1) into a reaction container, grinding and mixing to obtain slurry;

(3) Transferring the slurry obtained in the step (2) into spray drying equipment for spray drying granulation to obtain particles;

(4) Sintering the particles obtained in the step (3) to obtain the positive electrode active material.

In any embodiment, the manganese source may be a manganese-containing material known in the art to be useful in the preparation of lithium manganese phosphate, for example, the manganese source may be selected from one of elemental manganese, manganese dioxide, manganese phosphate, manganese oxalate, manganese carbonate, or a combination thereof.

The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, organic acid such as oxalic acid, etc., and can be oxalic acid, for example. The source of element R is selected from at least one of the group consisting of sulfate, borate, nitrate and silicate of element R. The source of element A is selected from at least one of the elements of A, oxides, phosphates, oxalates, carbonates and sulphates.

In some embodiments of the present application, the polyanionic positive electrode material includes Li _h A _i Mn _1-j B _j P _1-k C _k O _4- _l D _l Wherein a comprises one or more of Zn, al, na, K, mg, nb, mo and W; b comprises one or more elements of Ti, V, zr, fe, ni, mg, co, ga, sn, sb, nb and Ge; c comprises one or more elements of B, S, si and N; d comprises one or more elements of S, F, cl and Br; h is selected from the range of 0.9 to 1.1, i is selected from the range of 0.001 to 0.1, j is selected from the range of 0.001 to 0.5, k is selected from the range of 0.001 to 0.1, l is selected from the range of 0.001 to 0.1, and the polyanionic positive electrode material is electrically neutral.

Li _h A _i Mn _1-j B _j P _1-k C _k O _4-l D _l The compound is actually a specific LiMPO ₄ A material. The preparation method can refer to Li _1+x Mn _1-y A _y P _1-z R _z O ₄ The present invention is not limited thereto.

Hereinafter, li is used as _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001 The preparation process is further described: 1. preparing doped manganese oxalate: 1.3mol of MnSO ₄ ﹒H ₂ O, 0.7mol FeSO ₄ ﹒H ₂ O is fully mixed in a mixerAnd 6 hours. The mixture was transferred to a reaction vessel and 10L of deionized water and 2mol of oxalic acid dihydrate (calculated as oxalic acid) were added. The reaction vessel was heated to 80℃and stirred at 600rpm for 6 hours, and the reaction was terminated (no bubbles were generated) to obtain an Fe-doped manganese oxalate suspension. The suspension is then filtered, the filter cake is dried at 120℃and then ground to give a median particle diameter Dv ₅₀ Is Fe-doped manganese oxalate particles of about 100 nm. 2. Preparing doped lithium manganese phosphate: 1mol of the above manganese oxalate particles, 0.497mol of lithium carbonate, 0.001mol of Mo (SO ₄ ) ₃ An aqueous solution of phosphoric acid having a concentration of 85% containing 0.999mol of phosphoric acid, 0.001mol of H ₄ SiO ₄ NH 0.0005mol ₄ HF ₂ And 0.005mol sucrose was added to 20L deionized water. The mixture was transferred to a sand mill and sufficiently ground and stirred for 10 hours to obtain a slurry. Transferring the slurry into spray drying equipment for spray drying granulation, setting the drying temperature to 250 ℃, and drying for 4 hours to obtain particles. Sintering the powder at 700 ℃ for 10 hours in a protective atmosphere of nitrogen (90% by volume) +hydrogen (10% by volume) to obtain carbon-coated Li _0.994 Mo _0.001 Mn _0.65 Fe _0.35 P _0.999 Si _0.001 O _3.999 F _0.001 。

In some embodiments of the present disclosure, the first positive electrode active material further has a coating layer containing carbon.

The introduction of the carbon-containing coating layer improves the conductivity of the first positive electrode active material. At this time, the structure of the first positive electrode active material is actually LiMPO ₄ The core-shell structure is a core, and the surface of the core is coated with a coating layer.

In the list of the positive electrode materials, the molar content of Li is the initial state of the materials, namely the state before charging, and the molar content of Li can be changed after charge and discharge cycles when the positive electrode materials are applied to a battery system.

In addition, the molar content of O element is not always strict as the coefficient of O element in the chemical formula, and fluctuation, such as Li, occurs due to different preparation processes and conditions of the material _1+x Mn _1-y A _y P _1-z R _z O ₄ The molar content of O element in the composition is not strictly 4.

The first positive electrode active material may be, for example, liFePO ₄ 、LiMn _0.1 Fe _0.9 PO ₄ 、LiMn _0.2 Fe _0.8 PO ₄ 、LiMn _0.3 Fe _0.7 PO ₄ 、LiMn _0.4 Fe _0.6 PO ₄ 、LiMn _0.5 Fe _0.5 PO ₄ 、LiMn _0.6 Fe _0.4 PO ₄ 、LiMn _0.7 Fe _0.3 PO ₄ 、LiMn _0.8 Fe _0.2 PO ₄ 、LiMn _0.9 Fe _0.1 PO ₄ 、LiMnPO ₄ 、LiMn _0.5 Al _0.5 P _0.5 B _0.5 O ₄ 、LiMn _0.5 Mg _0.5 P _0.5 S _0.5 O ₄ Etc., liMPO ₄ The M in (2) comprises Mn and non-Mn elements, the non-Mn elements comprise one or two of a first doping element and a second doping element, the first doping element is doped with manganese, and the second doping element is doped with phosphorus. The first doping element comprises one or more elements of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge; the second doping element includes one or more elements of B, S, si and N.

In the technical solutions of some embodiments of the present application, the ternary system material includes a nickel cobalt manganese ternary material and its modified material, and a nickel cobalt aluminum ternary material and its modified material. The modified material of the nickel-cobalt-manganese ternary material and the modified material of the nickel-cobalt-aluminum ternary material refer to materials obtained by doping or cladding the nickel-cobalt-manganese ternary material or the nickel-cobalt-aluminum ternary material respectively. The coating layer contains one or more of oxides, nitrates, phosphates, carbonates of one or more elements of Al, ba, zn, ti, co, W, Y, si, sn, B, P, specifically Al ₂ O ₃ 、B ₂ O ₃ 、TiO ₂ Etc., exemplary, ternary system materials of the formula LiNi _x Co _y Mn _z O ₂ Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x+y+z=1.

In some embodiments of the present application, the ternary system material comprises Li _a Ni _b Co _c M1 _d M2 _e O _f R _g Wherein a is more than or equal to 0.75 and less than or equal to 1.2,0<b<1，0<c<1，0<d<E is more than or equal to 1 and less than or equal to 0.2,1, f is more than or equal to 0 and less than or equal to 2.5, g is more than or equal to 0 and less than or equal to 1, f+g is more than or equal to 3, M1 is one or two elements selected from Mn or Al, M2 is one or more elements selected from Zr, zn, cu, cr, mg, fe, V, ti, sr, sb, Y, W, nb, and R is one or more elements selected from N, F, S, cl.

The second positive electrode active material may be a ternary positive electrode material, specifically, liNi _0.4 Co _0.2 Mn _0.4 O ₂ 、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ And LiNi _0.7 Co _0.15 Mn _0.15 O ₂ And the like, wherein a in LiaNibCoCM1dM2eOfRg can be any one or more values in the range of 0.75-1.2, b can be any one or more values in the range of 0-1, c can be any one or more values in the range of 0-1, d can be any one or more values in the range of 0-1, e can be any one or more values in the range of 0-0.2, f can be any value in the range of 1-2.5, and g can be any one or more values in the range of 0-1.

The above list of the first positive electrode active material and the second positive electrode active material is only a list that can be implemented by the present solution, and is not limited to the present solution, and the first positive electrode active material and the second positive electrode active material are only required to meet the corresponding lattice shrinkage rate requirement. In other embodiments, those skilled in the art may select specific materials of the first positive electrode active material and the second positive electrode active material according to actual needs, for example, each of the materials listed above and modified materials thereof, modifications including doping or cladding, or other materials meeting the lattice shrinkage requirements of the present application.

After the foregoing description of the materials and structures of the positive electrode sheet 231, a specific description of the method for preparing the positive electrode sheet 231 follows.

The preparation method of the positive electrode sheet 231 includes the following steps: the order of preparing the positive electrode active material layer 2312 on the positive electrode current collector 2311, in which the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b in the positive electrode active material layer 2312 are prepared, is not limited, and may be: the first positive electrode active material layer 2312a is disposed on at least a portion of the surface of the positive electrode current collector 2311, and the second positive electrode active material layer 2312b is disposed on at least a portion of the surface of the first positive electrode active material remote from the positive electrode current collector 2311; it may also be: the second positive electrode active material layer 2312b is disposed on at least a portion of the surface of the positive electrode current collector 2311, and the first positive electrode active material layer 2312a is disposed on at least a portion of the surface of the second positive electrode active material layer 2312b remote from the positive electrode current collector 2311; the first positive electrode active material layer 2312a includes a first positive electrode active material, the second positive electrode active material layer 2312b includes a second positive electrode active material, and the lattice shrinkage a of the first positive electrode active material is greater than the lattice shrinkage b of the second positive electrode active material, and the relationship of the lattice shrinkage a of the first positive electrode active material, the lattice shrinkage b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312 satisfies: c is less than or equal to 0.014/(a-b).

The method satisfies the relationship of controlling the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material, and the ratio c of the thickness of the first positive electrode active material layer 2312a to the thickness of the positive electrode active material layer 2312: c is less than or equal to 0.014/(a-b), to reduce the occurrence of ion bridging of the first and second positive electrode active material layers 2312a and 2312b, thereby improving the electrical properties of the entire positive electrode sheet 231. Meanwhile, the first positive electrode active material and the second positive electrode active material are arranged in a layered manner, so that the possibility of current non-uniformity phenomenon between the first positive electrode active material and the second positive electrode active material can be reduced, and the positive electrode sheet 231 has higher capacity retention rate in the early period of circulation.

Fig. 7 is a flowchart of a method for preparing a positive electrode sheet 231 according to some embodiments of the present application, referring to fig. 7, the embodiment of the present application provides a method for preparing a positive electrode sheet 231, including:

s110, preparing first positive electrode active slurryAnd (3) material: the first positive electrode active material, the binder and the conductive agent are dispersed in a solvent to form a first positive electrode active slurry. The first positive electrode active material may be the first positive electrode active material described above, for example: the chemical formula is LiMn _a Fe _1-a PO ₄ The polyanion positive electrode material (a is more than or equal to 0 and less than or equal to 1), and a small amount of other positive electrode active materials can be optionally added.

For the specific selection of the polyanionic cathode material, reference may be made to the aforementioned selection of the polyanionic cathode material in the second cathode active material layer 2312b in the cathode sheet 231, and the details thereof will not be repeated here.

The binder can be one or more of styrene-butadiene rubber, water-based 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 may be one or more of dimethyl glutarate and N-methylpyrrolidone. Leveling agents, dispersing agents and the like can be added into the first positive electrode active slurry.

S120, preparing a second positive electrode 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 LiNi _x Co _y Mn _z O ₂ (x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x+y+z=1), and a small amount of other positive electrode active materials can be optionally added.

For the specific selection of the ternary system material, reference may be made to the aforementioned selection of the ternary system material in the first positive electrode active material layer 2312a in the positive electrode sheet 231, and the description thereof will not be repeated here.

The binder, the conductive agent, the solvent, and the like may be the binder in the first positive electrode active slurry, the conductive agent, the solvent, and the like, and the binder in the first positive electrode active slurry may be the same as or different from the binder in the second positive electrode active material; the conductive agent in the first positive electrode active slurry may be the same as or different from the conductive agent in the second positive electrode active material; the solvent in the first positive electrode active material 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.

S130, preparing a first positive electrode active material layer 2312a: the first positive electrode active slurry is coated on the surface of the positive electrode current collector 2311 and then dried to form a first positive electrode active material layer 2312a. The coating may be performed on one or both surfaces of the positive electrode current collector 2311 according to the need.

The coating mode can be as follows: blade coating, roll coating, slot coating, etc., the present application is not limited. The step S120 and the step S130 may be exchanged or performed simultaneously, and the present application is not limited thereto.

S140, a second positive electrode active material layer 2312b is prepared: the second positive electrode active slurry is coated on the surface of the first positive electrode active material layer 2312a, and then dried to form a second positive electrode active material layer 2312b. In the coating, the second positive electrode active material layer 2312b may be formed on the surface of the first positive electrode active material layer 2312a according to the condition of the first positive electrode active material layer 2312 a.

S150, rolling the second positive electrode active material layer 2312b to obtain the positive electrode sheet 231.

It should be noted that the above is merely an example in which the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b are sequentially disposed on the positive electrode current collector 2311, and in other embodiments, the first positive electrode active material layer 2312a and the second positive electrode active material layer 2312b may be exchanged in position.

After the positive electrode sheet 231 is prepared, sequentially stacking a first separator, the positive electrode sheet 231, a second separator and a negative electrode sheet, winding to form a wound flat structure, and then performing hot pressing to obtain a wound electrode assembly; or, 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 laminated to form a laminated electrode assembly.

The electrode assembly 23 may be used to manufacture a battery cell 20, and the battery cell 20 may be used to manufacture the secondary battery 100 and supply electric power to an electric device.

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

Examples and comparative examples

[ preparation of Positive electrode sheet ]

Preparing a first positive electrode active material layer: the preparation method comprises the following steps of mixing a first positive electrode active material, conductive agent carbon black and binder polyvinylidene fluoride (PVDF) according to a mass ratio of 96.5:1:2.5 adding the mixture into N-methyl pyrrolidone (NMP), and uniformly stirring and mixing to obtain first coating layer slurry; and then uniformly coating the slurry on the positive electrode current collector, and drying to obtain a first positive electrode active material layer.

Preparing a second positive electrode active material layer: the second positive electrode active material, conductive agent carbon black and binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 96.5:1:2.5 adding the mixture into N-methyl pyrrolidone (NMP), and uniformly stirring and mixing to obtain second coating layer slurry; and uniformly coating the slurry on the first positive electrode active material layer, drying, and rolling and die-cutting to obtain the positive electrode plate of the lithium ion battery.

[ preparation of negative electrode sheet ]

The active material artificial graphite, conductive agent carbon black, binder Styrene Butadiene Rubber (SBR) and thickener sodium hydroxymethyl cellulose (CMC) are mixed according to the mass ratio of 90:5:3:2, dissolving in deionized water serving as a solvent, and uniformly mixing to prepare negative electrode slurry; and uniformly coating the negative electrode slurry on a negative electrode current collector copper foil once or a plurality of times, and drying, cold pressing and cutting to obtain a negative electrode plate.

[ preparation of electrolyte ]

In an argon atmosphere glove box (H ₂ O<0.1ppm，O ₂ <0.1 ppm), mixing organic solvent Ethylene Carbonate (EC)/diethyl carbonate (DEC)/methyl ethyl carbonate (EMC) uniformly according to a volume ratio of 1/1/1, adding 1mol/L LiPF ₆ Uniformly dispersing lithium salt, and dissolving 5% fluoroethylene carbonate in the above-mentioned solutionAnd (3) uniformly stirring in an organic solvent to obtain the electrolyte.

[ isolation Membrane ]

Polyethylene film was used as the separator film.

[ preparation of Battery cell ]

And (3) preparing the prepared positive plate, negative plate and diaphragm (polyethylene (PE) porous polymeric film) into corresponding battery cells according to a Z-shaped lamination structure, vacuum drying the battery cells for 12 hours at 90 ℃, then performing ultrasonic welding on positive and negative electrode lugs, wherein the positive electrode adopts aluminum lugs, the negative electrode adopts nickel lugs, the positive and negative electrode lugs are positioned on the same side of the battery cells, filling the battery cells welded by the lugs into an aluminum plastic film with proper size for top side sealing, and immediately injecting electrolyte and sealing to obtain the uncharged battery. And the uncharged battery is subjected to the procedures of standing, hot and cold pressing, formation, shaping, capacity testing and the like in sequence, so that a battery monomer product is obtained.

The main parameter controls for examples and 1 to 8 and comparative examples 1 to 5 are shown in the following table:

in the above table, the first positive electrode active material having a lattice shrinkage of 6.50% was Li _0.945 Mn _0.6 Fe _0.4 P _0.995 S _0.005 O ₄ The first positive electrode active material with 6.80% lattice shrinkage is Li _0.947 Mn _0.7 Fe _0.38 Mg _0.02 P _0.994 S _0.005 B _0.001 O ₄ The first positive electrode active material with 6.20% lattice shrinkage is Li _0.955 Mn _0.3 Fe _0.65 V _0.05 P _0.995 S _0.005 O ₄ The second positive electrode active material with lattice shrinkage of 4.50% is LiNi _0.90 Co _0.03 Mn _0.05 B _0.01 Al _0.01 O ₂ The second positive electrode active material with lattice shrinkage of 4.40% is LiNi _0.80 Co _0.08 Mn _0.10 B _0.01 Al _0.01 O ₂ Second with lattice shrinkage of 2.50%The positive electrode active material is Li _0.99 ₉ Ni _0.55 Co _0.198 Mn _0.249 T _i0.001 Al _0.002 O ₂ 。

The lattice shrinkage test of the positive electrode active material includes: and (3) independently preparing the positive electrode active material into a soft-package laminated battery, charging to 4.3V according to 0.5C under the constant temperature environment of 25 ℃ and 2.5-4.3V, then charging to current of less than or equal to 0.05C under the constant voltage of 4.3V, then disassembling the battery to take out a positive electrode plate, performing XRD test, and finishing by XRD data and RietVeld software to obtain values of a and C axes (material unit cell parameters) required by calculating the unit cell volume of the positive electrode active material under the full charge state, wherein V full charge = a 2 x C x sin120 DEG, and obtaining V initial, wherein the lattice volume shrinkage rate= (V initial-V full charge)/V initial by adopting the same process to confirm the condition of the initial positive electrode active material which is not charged.

Comparative examples 6 to 8

Comparative examples 6 to 8 were used in a mixed coating form to co-use the first and second positive electrode active materials in one positive electrode active material layer, wherein the amounts of the first and second positive electrode active materials in comparative example 6 and comparative example 1, comparative example 7 and comparative example 2, and comparative example 8 and comparative example 3 were the same.

Comparative examples 9 to 16

Comparative examples 9 to 16 were used in a mixed coating form to co-use the first and second positive electrode active materials in one positive electrode active material layer, wherein the amounts of the first and second positive electrode active materials in comparative examples 9 and 1, comparative examples 10 and 2, comparative examples 11 and 3, comparative examples 12 and 4, comparative examples 13 and 5, comparative examples 14 and 6, comparative examples 15 and 7, and comparative examples 16 and 8 were the same.

Performance tests were performed on the batteries provided in each example and comparative example, and the performance tests specifically included:

and (3) testing the internal resistance increase of the circulating battery: discharging the battery monomer with 0 circle and 200 circles to 50% SOC at room temperature of 25 ℃, discharging by 4C current, and discharging the voltage difference DeltaU and DeltaU Current I _4C The ratio of (1) is the internal resistance R, i.e. R=DeltaU/I _4C The ratio of the internal resistance R of the battery cell of 200 cycles to 0 cycles is the internal resistance increase rate, i.e., (R _{Cycling 200 circles} - R _{Circulation for 0 circle} ）/R _{Circulation for 0 circle} 。

Capacity retention test: charging the battery monomer with 0 circle circulation and the battery monomer with 200 circles circulation to the upper limit voltage at room temperature of 25 ℃, adopting a capacity Cap discharged at 0.33 ℃, wherein the capacity retention rate is Cap _{Cycling 200 circles} /Cap _{Circulation for 0 circle} 。

The test results are shown in the following table:

as can be obtained from the table above, the battery cell assembled by the positive plate provided by the embodiment of the application has higher capacity retention rate and lower internal resistance increase.

As can be obtained by comparison of comparative examples 1 to 3 and examples 1 to 4, comparative example 4 and example 5, and comparative example 6, comparative example 5 and example 7, when the relationship of the lattice shrinkage a of the first positive electrode active material, the lattice shrinkage b of the second positive electrode active material, and the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: when c is less than or equal to 0.014/(a-b), the cycle retention rate of the battery cell can be controlled to be 93.3% or more, and the cycle internal resistance increase can be controlled to be 17% or less, while as the value of the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness is gradually increased, the capacity retention rate of the battery cell is gradually increased, while the internal resistance increase is gradually decreased.

As can be seen from the comparison of comparative examples 1 to 5 and comparative examples 8 to 16, the battery cells obtained by layering different positive electrode active materials have a high capacity retention rate and a low internal resistance increase.

The foregoing is merely a specific embodiment of the present application and is not intended to limit the application, and various modifications and variations may be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. The positive electrode sheet is characterized in that 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 first positive electrode active material layer comprises a first positive electrode active material, the second positive electrode active material layer comprises a second positive electrode active material, the lattice shrinkage rate a of the first positive electrode active material is larger than the lattice shrinkage rate b of the second positive electrode active material, and the relationship among the lattice shrinkage rate a of the first positive electrode active material, the lattice shrinkage rate b of the second positive electrode active material and the ratio c of the thickness of the first positive electrode active material layer to the thickness of the positive electrode active material layer is as follows: c is less than or equal to 0.014/(a-b);

Wherein the testing of the lattice shrinkage comprises: preparing a to-be-detected positive electrode active material into a soft-package laminated battery, charging to 4.3V according to 0.5C under the constant temperature environment of 25 ℃ and 2.5-4.3V, then charging to current of less than or equal to 0.05C under the constant voltage of 4.3V, disassembling the battery, taking out a positive plate, performing XRD test, and finishing by XRD data and RietVeld software to obtain the unit cell volume V of the positive electrode active material under the full charge state _{Full charge} The desired a, c axis values are according to the formula: v (V) _{Full charge} =a ² Xc×sin120 DEG to obtain V _{Full charge} The method comprises the steps of carrying out a first treatment on the surface of the XRD test is carried out on the initial positive electrode active material to be tested which is not charged, and the cell volume V of the positive electrode active material can be calculated in the initial state through XRD data and RietVeld software refinement _{Initial initiation} The desired values of the a, c axes are according to V _{Initial initiation} =a ² Xc×sin120 DEG to obtain V _{Initial initiation} The method comprises the steps of carrying out a first treatment on the surface of the Then according to the formula: lattice shrinkage= (V) _{Initial initiation} -V _{Full charge} ）/V _{Initial initiation} The lattice shrinkage is obtained.

2. The positive electrode sheet according to claim 1, wherein the relationship of the lattice shrinkage a of the first positive electrode active material, the lattice shrinkage b of the second positive electrode active material, and the ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: c is less than or equal to 0.01/(a-b).

3. The positive electrode sheet according to claim 1 or 2, wherein a ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: 80 percent or more and 20 percent or more of c.

4. The positive electrode sheet according to claim 3, wherein a ratio c of the first positive electrode active material layer thickness to the positive electrode active material layer thickness satisfies: 70 percent or more and 30 percent or more of c.

5. The positive electrode sheet according to claim 1 or 2, wherein the first positive electrode active material has a lattice shrinkage a of 6.2% to 6.8%; and/or

The lattice shrinkage rate b of the second positive electrode active material is 2.5% -4.5%.

6. The positive electrode sheet according to claim 1 or 2, wherein the first positive electrode active material comprises a polyanionic positive electrode material; and/or

7. The positive electrode sheet according to claim 6, wherein the polyanionic positive electrode material comprises LiMPO ₄ M comprises Mn and non-Mn elements, wherein the non-Mn elements comprise one or two of a first doping element and a second doping element, the first doping element is doped with manganese, and the second doping element is doped with phosphorus; and/or

The ternary system material comprises a nickel-cobalt-manganese ternary material, a modified material thereof, a nickel-cobalt-aluminum ternary material and a modified material thereof.

8. The positive electrode sheet of claim 7, wherein the first doping element comprises one or more of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge; and/or

The second doping element includes one or more elements of B, S, si and N.

9. The positive electrode sheet according to claim 6, wherein the polyanionic positive electrode material comprises Li _1+x Mn _1- _y A _y P _1-z R _z O ₄ Wherein x is any number in the range of-0.100 to 0.100, y is any number in the range of 0.001 to 0.500, z is any number in the range of 0.001 to 0.100, A comprises one or more elements of Zn, al, na, K, mg, mo, W, ti, V, zr, fe, ni, co, ga, sn, sb, nb and Ge, and R comprises one or more elements of B, S, si and N.

10. The positive electrode sheet according to claim 6, wherein the polyanionic positive electrode material comprises Li _h A _i Mn _1-j B _j P _1-k C _k O _4-l D _l Wherein the a comprises one or more of Zn, al, na, K, mg, nb, mo and W; the B includes one or more elements of Ti, V, zr, fe, ni, mg, co, ga, sn, sb, nb and Ge; the C includes one or more elements of B, S, si and N; the D comprises one or more elements of S, F, cl and Br; the h is selected from the range of 0.9 to 1.1, the i is selected from the range of 0.001 to 0.1, the j is selected from the range of 0.001 to 0.5, the k is selected from the range of 0.001 to 0.1, the l is selected from the range of 0.001 to 0.1, and the polyanionic positive electrode material is electrically neutral.

11. The positive electrode sheet according to claim 6, wherein the polyanionic positive electrode material further has a coating layer containing carbon.

12. The positive electrode sheet according to claim 6, wherein the ternary system material includes Li _a Ni _b Co _c M1 _d M2 _e O _f R _g Wherein a is more than or equal to 0.75 and less than or equal to 1.2,0<b<1，0<c<1，0<d<E is more than or equal to 1 and less than or equal to 0.2,1, f is more than or equal to 0 and less than or equal to 2.5, g is more than or equal to 0 and less than or equal to 1, f+g is more than or equal to 3, M1 is one or two elements selected from Mn or Al, M2 is one or more elements selected from Zr, zn, cu, cr, mg, fe, V, ti, sr, sb, Y, W, nb, and R is one or more elements selected from N, F, S, cl.

13. A battery cell, characterized in that the battery cell comprises the positive electrode sheet according to any one of claims 1 to 12.

14. A battery comprising the cell of claim 13.

15. An electrical device comprising the battery cell of claim 13 or the battery of claim 14.