CN115020635A

CN115020635A - Positive plate, lithium ion battery and vehicle

Info

Publication number: CN115020635A
Application number: CN202210672625.7A
Authority: CN
Inventors: 曾士哲
Original assignee: Weilai Automobile Technology Anhui Co Ltd
Current assignee: Weilai Automobile Technology Anhui Co Ltd
Priority date: 2022-06-14
Filing date: 2022-06-14
Publication date: 2022-09-06

Abstract

The invention relates to the technical field of batteries, and particularly provides a positive plate, a lithium ion battery and a vehicle, aiming at solving the problem that the cycle performance of the lithium ion battery is influenced by serious deterioration of the conventional positive plate at the later stage of the life cycle of the lithium ion battery. For this purpose, the positive plate comprises a positive current collector, wherein at least one of a first side surface and a second side surface, which are opposite to each other, of the positive current collector is provided with N doped modified active material layers, each doped modified active material layer comprises an active material, the active material is doped with a first element and a second element, and the doped modified active material layer closest to the positive current collector has low content of the first element and high content of the second element relative to the doped modified active material layer farthest from the positive current collector, so that the active material more resistant to deep charge and discharge is distributed in the surface area of the positive plate, the consistency of the whole lithium intercalation and deintercalation of the positive plate is improved, and a series of problems and hidden dangers caused by excessive charge and discharge on the surface of the positive plate are reduced.

Description

Positive plate, lithium ion battery and vehicle

Technical Field

The invention relates to the technical field of batteries, and particularly provides a positive plate, a lithium ion battery and a vehicle.

Background

With the continuous and high-speed development of the fields of large-scale energy storage, electric vehicles, consumer electronics and the like, the demand for lithium ion batteries is also continuously increased, and various performances such as energy density, quick charging capability, safety and reliability and the like are approaching to the limit more and more.

At present, in order to improve the energy density of a high-energy-density power battery, high-nickel NCM is mostly selected as an anode active substance, the charge and discharge resistance of each layer of anode active substance is the same, and the coating thickness of an anode plate is increased, so that the difference of lithium intercalation degrees of the anode active substance at different distances from the surface of the anode plate along the direction perpendicular to the thickness direction of the anode plate is increased, the higher the lithium deintercalation degree of the NCM material closer to the surface layer of the anode plate is, the more obvious the problem is reflected at the later stage of the cycle, the NCM material on the surface layer of the anode plate is seriously deteriorated, the cycle performance of the battery is influenced, and the problems of gas generation, reliability risk and the like are also caused.

Therefore, there is a need in the art for a new positive electrode sheet, lithium ion battery and vehicle to solve the above problems.

Disclosure of Invention

The invention aims to solve the technical problems, namely, the problems that the cycle performance of the lithium ion battery is influenced by serious deterioration of the conventional positive plate in the later period of the life cycle of the lithium ion battery are solved.

In a first aspect, the present invention provides a positive electrode sheet, including a positive electrode current collector, where the positive electrode current collector includes a first side surface and a second side surface that are opposite to each other, at least one of the first side surface and the second side surface is provided with N layers of doped modified active material layers, each layer of the doped modified active material layer includes an active material, the active material is doped with a first type of element and a second type of element, and a doped modified active material layer closest to the positive electrode current collector has a low content of the first type of element and a high content of the second type of element relative to a doped modified active material layer farthest from the positive electrode current collector; wherein N is the total number of the doped modified active material layers, N is a positive integer, and N is more than 1.

In a preferred technical solution of the positive electrode sheet, a content of the first type element doped in the ith active material layer is less than a content of the first type element doped in the (i + 1) th active material layer; the content of the doped second type element in the ith active material layer is greater than or equal to that in the (i + 1) th active material layer; and i is the number of layers where the active material layers are located, the ith active material layer is close to the positive current collector, the (i + 1) th active material layer is far away from the positive current collector, i is a positive integer, and i is more than or equal to 1 and less than N.

In a preferred technical scheme of the positive plate, the first element is selected from at least one or more of titanium, magnesium, aluminum, pickaxe, iron, niobium, molybdenum, tungsten, fluorine and boron.

In a preferred embodiment of the above positive electrode sheet, the first type element is selected from a combination of aluminum and magnesium, a combination of aluminum, titanium and fluorine, a combination of magnesium, iron and boron, a combination of molybdenum, niobium and tungsten, a combination of aluminum, niobium and fluorine, or a combination of aluminum, magnesium and titanium.

In a preferred embodiment of the positive electrode sheet, the total content of the first type element doped in each active material layer satisfies the following formula:

((i-1)/(N-1))×5000+500≤P≤((i-1)/(N-1))×8000+6000

wherein P is a total content of the first type element contained in the active material layer, and a unit of P is ppm.

In a preferred embodiment of the positive electrode sheet, the second element is at least one or more selected from copper, calcium, sulfur and chlorine.

In a preferred embodiment of the positive electrode sheet, the second element is selected from sulfur, a combination of sulfur and chlorine, a combination of sulfur and copper, or a combination of chlorine and calcium.

In a preferred embodiment of the positive electrode sheet, a total content of the second type element doped in each active material layer satisfies the following formula:

0＜Q≤1000-((i-1)/(N-1))×600

wherein Q is the total content of the second type element doped in the active material layer, and the unit of Q is ppm.

In a preferred embodiment of the positive electrode sheet, the material of the active material layer is selected from a ternary NCM active material, a lithium iron phosphate active material, or a lithium-rich manganese-based active material.

In a preferred embodiment of the positive electrode sheet, the active material is selected from ternary NCM active materials.

In a preferred technical scheme of the positive plate, the ternary NCM active material is at least one or more of single crystal particles, polycrystalline particles and secondary particles.

In a preferred embodiment of the positive electrode sheet, when the ternary NCM active material is a single crystal particle, the average number of cracks per ternary NCM single crystal particle in the x-th active material layer and the y-th active material layer satisfies the following formula:

0＜|(X-Y)/((x-y)/(N-1))|＜3

wherein x is the number of layers where the xth active material layer is located; x is the number of cracks per ternary NCM single crystal grain on average in the xth active material layer; y is the number of the layers where the y active material layer is located; y is the number of cracks that each ternary NCM single crystal grain has on average in the Y-th active material layer.

In a second aspect, the present invention provides a lithium ion battery, including the positive electrode sheet according to any one of the above preferred embodiments.

In a third aspect, the present invention provides a vehicle including the positive electrode sheet or the lithium ion battery according to any one of the above preferred embodiments.

In the preferred technical scheme of the positive plate, the positive plate comprises a positive current collector, the positive current collector comprises a first side surface and a second side surface which are opposite, at least one of the first side surface and the second side surface is provided with N layers of doping modified active material layers, each layer of doping modified active material layer comprises an active material, the active material is doped with a first type of element and a second type of element, and the doping modified active material layer closest to the positive current collector has low content of the first type of element and high content of the second type of element relative to the doping modified active material layer farthest from the positive current collector; wherein N is the total number of the doped modified active material layers, N is a positive integer, and N is more than 1.

Compared with the technical scheme that each active material layer in the prior art has the same charge-discharge tolerance, the doping modified active material layer farthest from the positive current collector is rich in the first element and is lack of the second element relative to the doping modified active material layer closest to the positive current collector, and through the arrangement, the active material more tolerant to deep charge-discharge is distributed in the surface layer area of the positive plate, so that the integral lithium desorption consistency of the positive plate is improved, the lattice collapse of the surface layer modified material of the positive plate caused by excessive lithium ion desorption of the positive plate in single lithium desorption is avoided, the lattice can keep a complete structure, the stability of the structure of the positive plate in the long-term lithium desorption process is improved, the serious deterioration of the surface layer modified material of the positive plate is avoided, and the oxygen generated by the serious deterioration of the surface layer modified material of the positive plate is reduced, The number of hydrogen, carbon dioxide, carbon monoxide and other gases prolongs the service life of the positive plate, and improves the cycle performance and reliability of the lithium ion battery.

Furthermore, the content of the first type of element doped in the ith active material layer close to the positive current collector is less than the content of the first type of element doped in the (i + 1) th active material layer far away from the positive current collector, the content of the second type of element doped in the ith active material layer close to the positive current collector is greater than or equal to the content of the second type of element doped in the (i + 1) th active material layer far away from the positive current collector, namely, the content of the first type of element doped in the (i + 1) th active material layer relatively far away from the positive current collector is increased, and the content of the second type of element doped in the (i + 1) th active material layer relatively far away from the positive current collector is reduced, through the structural arrangement, the tolerance degree of the lithium deintercalation of the (i + 1) th active material layer relatively far away from the positive current collector is greater than the tolerance degree of the lithium deintercalation (i) th active material layer close to the positive current collector, and therefore, the charge-discharge tolerance of the N-layer doped modified active material layer is gradually improved along the direction far away from the positive current collector, so that the tolerance degree of the de-intercalated lithium on the surface layer of the positive plate is maximized, the serious deterioration of the material of the surface layer of the positive current collector in the last cycle stage of the lithium ion battery is further avoided, and the cycle performance and the reliability of the lithium ion battery are further improved.

Further, when the ternary NCM active material is a single crystal grain, the x-th active material layer and the y-th active material layer have an average number of cracks per ternary NCM single crystal grain satisfying the following formula: 0 < | (X-Y)/((X-Y)/(N-1)) | < 3, namely, the proportion relation among the average number of cracks of each ternary NCM single crystal particle in any two layers of active material layers, the number of corresponding active material layers and the total number of doped modified active material layers is controlled to be 0-3, so that the average number of cracks of each ternary NCM single crystal particle in each active material layer is reduced, the capacity loss of each active material layer is reduced, and the aging speed of the lithium ion battery is reduced.

Scheme 1 discloses a positive plate, which is characterized in that the positive plate comprises a positive current collector, the positive current collector comprises a first side surface and a second side surface which are opposite, at least one of the first side surface and the second side surface is provided with N layers of doped modified active material layers, each layer of doped modified active material layer comprises an active material, and the active material is doped with a first element and a second element,

the doping modified active material layer closest to the positive current collector has low content of the first type of element and high content of the second type of element relative to the doping modified active material layer farthest from the positive current collector;

wherein N is the total number of the doped modified active material layers, N is a positive integer, and N is more than 1.

Scheme 2, the positive electrode sheet according to scheme 1, wherein the content of the first type element doped in the i-th active material layer is less than the content of the first type element doped in the i + 1-th active material layer;

the content of the doped second type element in the ith active material layer is greater than or equal to that in the (i + 1) th active material layer;

and i is the number of layers where the active material layers are located, the ith active material layer is close to the positive current collector, the (i + 1) th active material layer is far away from the positive current collector, i is a positive integer, and i is more than or equal to 1 and less than N.

Scheme 3, the positive plate according to scheme 2, characterized in that the first type element is selected from at least one or more of titanium, magnesium, aluminum, zirconium, iron, niobium, molybdenum, tungsten, fluorine, boron.

Scheme 4, the positive electrode sheet according to scheme 3, wherein the first type element is selected from a combination of aluminum and magnesium, a combination of aluminum, titanium and fluorine, a combination of magnesium, iron and boron, a combination of molybdenum, niobium and tungsten, a combination of aluminum, zirconium and fluorine, or a combination of aluminum, magnesium and titanium.

The positive electrode sheet according to claim 5, 3 or 4, wherein the total content of the first type element doped in each active material layer satisfies the following formula:

((i-1)/(N-1))×5000+500≤P≤((i-1)/(N-1))×8000+6000

wherein P is the total content of the first element doped in the active material layer, and the unit of P is ppm.

Scheme 6 and the positive electrode sheet according to scheme 2, wherein the second element is at least one or more selected from copper, calcium, sulfur and chlorine.

The positive electrode sheet according to claim 7 or 6, wherein the second element is selected from the group consisting of sulfur, a combination of sulfur and chlorine, a combination of sulfur and copper, and a combination of chlorine and calcium.

The positive electrode sheet according to claim 8, claim 6, or claim 7, wherein the total content of the second type element doped in each active material layer satisfies the following formula:

0＜Q≤1000-((i-1)/(N-1))×600

Scheme 9, the positive electrode sheet according to any one of schemes 1 to 4, wherein the active material is selected from a ternary NCM active material, a lithium iron phosphate active material, or a lithium-rich manganese-based active material.

Scheme 10, the positive electrode sheet according to scheme 9, wherein the active material is selected from ternary NCM active materials.

Scheme 11 and the positive electrode sheet according to scheme 10, wherein the ternary NCM active material is at least one or more of single crystal particles, polycrystalline particles, and secondary particles.

Scheme 12 is the positive electrode sheet according to claim 11, wherein when the ternary NCM active material is a single crystal particle, the average number of cracks per ternary NCM single crystal particle in the x-th active material layer and the y-th active material layer satisfies the following formula:

0＜|(X-Y)/((x-y)/(N-1))|＜3

The lithium ion battery according to claim 13 is characterized by comprising the positive electrode sheet according to any one of claims 1 to 12.

The vehicle according to claim 14 is characterized by comprising the positive electrode sheet according to any one of claims 1 to 12 or the lithium ion battery according to claim 13.

Drawings

The positive electrode sheet of the present invention is described below with reference to the accompanying drawings, in which:

fig. 1 is a schematic view of the structure of the positive electrode sheet of the present invention.

List of reference numerals

1. A positive current collector;

2. doping the modified active material layer; 21. 1 st active material layer; 22. a 2 nd active material layer;

3. a diaphragm.

Detailed Description

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention. For example, although the present application is described in conjunction with an electric vehicle, the technical solution of the present invention is not limited thereto, and the positive electrode sheet may be obviously applied to other vehicles such as a hybrid vehicle, without departing from the principle and scope of the present invention.

It should be noted that in the description of the present invention, the terms of direction or positional relationship indicated by the terms "upper", "lower", etc. are based on the directions or positional relationships shown in the drawings, which are for convenience of description only, and do not indicate or imply that the device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and "tenth" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Based on the technical problems proposed in the background art, the invention provides a positive plate, which aims to arrange an N-layer doped modified active material layer on at least one of a first side surface and a second side surface of a positive plate current collector opposite to each other, and arrange the doped modified active material layer farthest from the positive plate current collector to be rich in a first element and lack of a second element relative to the doped modified active material layer closest to the positive plate current collector, so that the active material more resistant to deep charge and discharge is distributed in the surface layer area of the positive plate, the integral lithium desorption consistency of the positive plate is improved, the lattice collapse of the surface layer modified material of the positive plate caused by excessive lithium ion desorption of the positive plate in single lithium desorption is avoided, the complete structure of the lattice can be maintained, the stability of the structure of the positive plate in the long-term lithium desorption process is improved, and the serious deterioration of the surface layer modified material of the positive plate is avoided, the quantity of oxygen, hydrogen, carbon dioxide, carbon monoxide and other gases generated by serious deterioration of the surface modified material of the positive plate is reduced, the service life of the positive plate is prolonged, and the cycle performance and reliability of the lithium ion battery are improved.

Referring first to fig. 1, the positive electrode sheet of the present invention will be described. Fig. 1 is a schematic structural view of the positive electrode sheet of the present invention.

As shown in fig. 1, the positive electrode sheet of the present invention includes a positive electrode current collector 1, the positive electrode current collector 1 includes a first side surface and a second side surface opposite to each other in a thickness direction (i.e., a direction from bottom to top in fig. 1), the first side surface (i.e., the side surface shown in fig. 1) of the positive electrode current collector 1 is provided with N layers of doped modified active material layers 2, each layer of doped modified active material layer 2 includes an active material, the active material layer is doped with a first type of element and a second type of element, and the doped modified active material layer closest to the positive electrode current collector 1 has a lower first type of element content and a higher second type of element content relative to the doped modified active material layer farthest from the positive electrode current collector 1, that is, the doped modified active material layer farthest from the positive electrode current collector 1 contains the first type of element and lacks the second type of element relative to the doped modified active material layer closest to the positive electrode current collector 1, and the charge and discharge resistance of the doped modified active material layer farthest from the positive current collector is higher than that of the doped modified active material layer closest to the positive current collector, wherein N is the total number of doped modified active material layers, N is a positive integer, and N is greater than 1.

Preferably, a plurality of doping modification active material layers 2 may be sequentially coated on the first side of the positive electrode current collector 1, or a plurality of doping modification active material layers 2 may also be simultaneously coated, that is, a plurality of doping modification active material layers 2 are simultaneously coated on the first side of the positive electrode current collector 1. Wherein, the naming serial numbers of the doping modified active material layers 2 gradually increase along the direction far away from the positive electrode current collector 1, taking two doping modified active material layers as an example, the doping modified active material layer near the positive electrode current collector 1 is named as a 1 st active material layer 21, and the doping modified active material layer far away from the positive electrode current collector 1 is named as a 2 nd active material layer 22.

Further, one of gravure coating, transfer coating, extrusion coating and spray coating may be selected to coat the doped modified active material layer 2, and of course, two, three or more of the coating manners may also be selected to coat the doped modified active material layer 2, and a person skilled in the art may determine a specific coating manner according to actual process requirements, and the invention is not limited thereto.

Further, a separator 3 may be provided on a surface of the doping modification active material layer (for example, the 2 nd doping modification active material layer 22 shown in fig. 1) farthest from the positive electrode collector 1.

The positive current collector 1 is made of metal foil such as aluminum foil, copper foil, nickel foil and the like.

Although fig. 1 shows two layers, that is, the 1 st active material layer 21 and the 2 nd active material layer 22, this is merely an example and is not a limitation, and in practical applications, any layer of the doping modification active material layers 2, such as three layers, four layers, five layers, six layers, seven layers, eight layers, nine layers, ten layers or eleven layers, may be provided, and those skilled in the art may flexibly adjust and set the number of the doping modification active material layers 2 according to the requirement of the actual positive electrode sheet for withstanding charge and discharge capacity, and the like.

In addition, in practical application, a plurality of layers of doping modified active material layers 2 may be disposed on both side surfaces of the positive electrode current collector 1 in the thickness direction, and a person skilled in the art may flexibly adjust and set the disposition position of the doping modified active material layer 2 on the positive electrode current collector 1 according to the actual demand of the lithium ion battery product, and the like.

Next, the first type element doped in the active material will be explained.

Firstly, the content of the first type element doped in two adjacent active material layers is set as follows: the content of the first type element doped in the i-th active material layer close to the positive electrode current collector 1 is smaller than the content of the first type element doped in the i + 1-th active material layer far from the positive electrode current collector 1, for example, in conjunction with fig. 1, the content of the first type element doped in the 1-th active material layer (i.e., the active material layer of the 1-th doping modification active material layer 21 shown in fig. 1) is smaller than the content of the first type element doped in the 2-th active material layer (i.e., the active material layer of the 2-th doping modification active material layer 22 shown in fig. 1), i.e., the content of the first type element doped in the 2-th active material layer is increased relative to the 1-th active material layer. Wherein i is the number of layers where the active material layer is located, i is a positive integer, i is greater than or equal to 1 and less than N, and further i +1 is equal to N.

Further, the total content of the first type element doped in each active material layer is set to satisfy the following formula (1):

((i-1)/(N-1))×5000+500≤P≤((i-1)/(N-1))×8000+6000 (1)

in formula (1), P is the total content of the first type element doped in the active material layer, and the unit of P is ppm.

For example, N is 2, when i is 1 (i.e., the 1 st doping modification active material layer 21 shown in FIG. 1), 500. ltoreq. P. ltoreq.6000; when i is 2 (i.e., the 2 nd doping modification active material layer 22 shown in FIG. 1), P.ltoreq.5500.ltoreq.14000 accurately defines a range of the total content of the first type element that can be doped in each active material layer, and a person skilled in the art can flexibly adjust the total content of the first type element that can be doped in each active material layer within the range.

Wherein, the first element is selected from one, two, three or more of titanium, magnesium, aluminum, zirconium, iron, niobium, molybdenum, tungsten, fluorine and boron, preferably the combination of aluminum and magnesium, the combination of aluminum, titanium and fluorine, the combination of magnesium, iron and boron, the combination of molybdenum, niobium and tungsten, the combination of aluminum, zirconium and fluorine, or the combination of aluminum, magnesium and titanium, and other combinations, the skilled person can flexibly adjust the combination of the first elements listed above according to the actual lithium ion battery product requirements, and the like, and in any way, the total content of the first elements corresponding to any combination is within the range determined according to the formula (1).

Next, the second type of element doped in the active material layer will be explained.

Firstly, the content of the second type element doped in two adjacent active material layers is set as follows: the content of the second type element doped in the ith active material layer close to the positive electrode current collector 1 is greater than or equal to the content of the second type element doped in the (i + 1) th active material layer far from the positive electrode current collector 1, for example, in conjunction with fig. 1, the content of the second type element doped in the 1 st active material layer is greater than the content of the second type element doped in the 2 nd active material layer, that is, the content of the second type element doped in the 2 nd active material layer is reduced relative to the 1 st active material layer.

Further, the total content of the second type element doped in each active material layer is set to satisfy the following formula (2):

0＜Q≤1000-((i-1)/(N-1))×600 (2)

in the formula (2), Q is the total content of the second type element doped in the active material layer, and the unit of Q is ppm.

For example, N is 2, when i is 1 (i.e., the 1 st doping modification active material layer 21 shown in FIG. 1), 0 < Q.ltoreq.1000; when i is 2 (i.e., the 2 nd doping modification active material layer 22 shown in FIG. 1), 0 < Q ≦ 400, a range of the total content of the second type element that can be doped in each active material layer is accurately defined, and a person skilled in the art can flexibly adjust the total content of the second type element that can be doped in each active material layer within the range.

The second type element is selected from one or two or more of copper, calcium, sulfur and chlorine, and preferably sulfur, a combination of sulfur and chlorine, a combination of sulfur and copper, or a combination of chlorine and calcium, and other combinations are preferable, and those skilled in the art can flexibly adjust the combinations of the above-mentioned second type elements according to actual use requirements, so long as the total content of the second type elements corresponding to any combination is within the range determined by the formula (2).

Through the structure arrangement, the content of the first element doped in the active material layer relatively far away from the positive current collector 1 is improved, and the content of the second element doped in the active material layer relatively far away from the positive current collector 1 is reduced, so that the tolerance degree of the de-intercalated lithium of the active material layer relatively far away from the positive current collector 1 is improved, the charge and discharge tolerance capability of the N-layer doped modified active material layer 2 is gradually improved along the direction far away from the positive current collector, the tolerance degree of the de-intercalated lithium of the surface layer of the positive plate (i.e. the doped modified active material layer farthest from the positive current collector 1 in the figure 1) is maximum, the serious deterioration of the surface layer material of the positive current collector 1 in the cycle end stage of the lithium ion battery is further avoided, and the cycle performance and the reliability of the lithium ion battery are further improved.

Next, the active material will be explained.

Preferably, the material of the active material is selected from ternary NCM active materials, wherein the ternary NCM active material may be single crystal grains, polycrystalline grains or secondary grains, or the ternary NCM active material may also be a mixture of two or three of single crystal grains, polycrystalline grains and secondary grains. In addition, in practical applications, other positive electrode active materials such as a lithium iron phosphate active material and a lithium-rich manganese-based active material may be used as the active material, but these are not necessarily listed here.

Further, when the ternary NCM active material is a single crystal particle, after 500 cycles of 1.5C charge/1C discharge in a 45 ℃ environment of a cell of a lithium ion battery, the number of cracks per ternary NCM single crystal particle in the x-th active material layer and the y-th active material layer on average is set to satisfy the following formula (3):

0＜|(X-Y)/((x-y)/(N-1))|＜3 (3)

in the formula (3), x is the number of layers where the xth active material layer is located; x is the number of cracks per ternary NCM single crystal grain on average in the xth active material layer; y is the number of the layers where the y active material layer is located; y is the number of cracks per ternary NCM single crystal particle on average in the Y-th active material layer; wherein x and y are different.

For example, N is 2, and when i is 1 (i.e., the 1 st doping modification active material layer 21 shown in fig. 1), X is 3; when Y is 2 (i.e., the 2 nd doping modified active material layer 22 shown in fig. 1), Y is 1.6, calculated according to the formula (3), | (3-1.6)/((1-2)/(2-1)) | 1.4, and 1.4 is between 0 and 3, that is, the proportional relationship among the average number of cracks per ternary NCM single crystal particle in any two active material layers, the number of layers of the corresponding active material layers, and the total number of layers of the doping modified active material layers 2 is controlled between 0 and 3, so that the average number of cracks per ternary NCM single crystal particle in each active material layer is reduced, the capacity loss of each active material layer is reduced, and the aging speed of the lithium ion battery is reduced.

The method for testing the crushing degree of the ternary NCM single crystal particles comprises the following steps: under the environment that the battery core of the lithium ion battery is at 45 ℃, after 500 cycles of 1.5C charging/1C discharging, respectively observing the section photos of a fresh battery prepared by using an argon ion grinder CP and a positive plate after high-temperature cycling by utilizing SEM, selecting a plurality of SEM pictures, and selecting the particle size of 0.5 XD ₅₀ To 2 XD ₅₀ 50 single crystal NCM particles in between, with the number of cracks at the corresponding positions calculated, respectively.

It should be noted that the test conditions for the degree of fragmentation of ternary NCM single crystal particles are not limited to the above-mentioned conditions, and for example, the cell of a lithium ion battery may be placed in an environment of 25 ℃ and cycled for 450 times at 1C/1C, and those skilled in the art may flexibly adjust and set the test conditions according to actual detection requirements and the like.

Next, the doping method of the elements will be described by taking the ternary NCM active material as an example, where the first type of elements are aluminum and magnesium, and the second type of elements are sulfur.

Firstly, pouring a ternary NCM active material, aluminum oxide, magnesium oxide and manganese sulfide into a high-speed mixer for mixing to obtain a uniformly mixed material; and secondly, pre-calcining the uniformly mixed material at 500-550 ℃ for 300-400 min, and then calcining at 700-750 ℃ for 800-900 min, wherein the temperature rise rates in the pre-calcining stage and the calcining stage are respectively 3-5 ℃/min, and the NCM active material doped with aluminum, magnesium and sulfur is obtained after calcining.

It should be noted that, although the above list is aluminum oxide, magnesium oxide and manganese sulfide, in practical applications, those skilled in the art can adjust and set other substances such as oxides, salts and the like containing elements to be doped according to the elements to be doped, for example, manganese sulfate, aluminum sulfate, titanium oxide and the like, which are not listed here.

It should be noted that the doping method of the element is not limited to the above-mentioned method, and other methods may be adopted, and the present invention is not limited thereto as long as the element can be doped.

Next, the other raw materials contained in each layer of the doping modified active material layer 2 will be further described.

Preferably, each of the doped modified active material layers further comprises a thickener, a conductive agent, a binder, and an organic solvent.

Wherein the thickener is selected from sodium carboxymethylcellulose or lithium carboxymethylcellulose.

The conductive agent is selected from conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, graphene, single-wall or multi-wall carbon nanotube, metal powder, carbon fiber and the like.

Wherein the binder is selected from styrene butadiene rubber, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide, polyvinylidene fluoride and the like.

Wherein the organic solvent is selected from N-methyl pyrrolidone, ethylene carbonate, methyl formate, diglyme, etc.

The positive electrode sheet of the present invention will be described in further detail below by taking a ternary NCM active material as an example and combining the examples and comparative examples.

Comparative example 1: single layer of doped modified active material layer

Step 1: the preparation method comprises the following steps of mixing a negative electrode active material artificial graphite, a thickening agent sodium carboxymethyl cellulose (CMC-Na), a binder styrene butadiene rubber and a conductive agent conductive carbon black according to a weight ratio of 98%: 0.7%: 0.8%: 0.5 percent of the mixture is mixed, deionized water is added, negative electrode slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the negative electrode slurry is 40-49 percent, the viscosity is 2000-6000 mPa.s, and the negative electrode slurry is coated on a copper foil with the thickness of 5 mu m by an extrusion coating machine according to an extrusion coating mode, so that the coating process is completed. And then drying, cold pressing and stripping to finish the preparation of the cathode plate.

And 2, step: obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the components are mixed, NMP (N-methyl pyrrolidone) is added, positive electrode slurry is obtained under the action of a vacuum mixer, wherein the solid content of the positive electrode slurry is 70-80 percent, the viscosity is 3500-6500 mPa.s, and the positive electrode slurry is coated on an aluminum foil with the thickness of 10 mu m by an extrusion coating machine according to an extrusion coating mode, so that the coating process is completed. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein, the total content of the first element Al and Mg is 8000 ppm; the total content of the second type of element S was 200ppm, the content of the first type of element was higher and the content of the second type of element was lower, relative to comparative example 2.

And 3, step 3: and (3) respectively die-cutting the negative plate obtained in the step (1) and the positive plate obtained in the step (2), laminating the negative plate and the diaphragm together to prepare a naked battery cell, putting the naked battery cell into a packaging bag, and completing the preparation of the battery cell of the lithium ion battery through the processes of liquid injection, formation, capacity grading, standing and the like.

Comparative example 2: single layer of doped modified active material layer

Step 1: same as in comparative example 1, step 1.

Step 2: obtaining PVDF, conductive carbon black and secondary particle NCM811 material with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the mixture is mixed, NMP is added, positive electrode slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the positive electrode slurry is 70-80 percent, the viscosity is 3500-6500 mPa.s, and the positive electrode slurry is coated on an aluminum foil with the thickness of 10 mu m by an extrusion coating machine according to an extrusion coating mode, so that the coating procedure is completed. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein the total content of the first type elements Al and Mg is 1500 ppm; the total content of the second type of element S was 800ppm, the content of the first type of element being lower and the content of the second type of element being higher with respect to comparative example 1.

And 3, step 3: same as in step 3 of comparative example 1.

Comparative example 3: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

and simultaneously coating the 1 st active material layer slurry and the 2 nd active material layer slurry on an aluminum foil with the thickness of 10 microns by adopting a double-layer coating machine, coating the 1 st active material layer slurry on a region close to the aluminum foil, and coating the 2 nd active material layer slurry on a region far away from the aluminum foil to finish the coating process. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein, the total content of the first type element Al and Mg in the 1 st active material layer is 8000ppm, and the total content of the second type element S is 200 ppm; the total content of the first type elements Al and Mg of the 2 nd active material layer was 1500ppm, and the total content of the second type element S was 800 ppm. Further, the first type element content of the 1 st active material layer is higher relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is lower relative to the second type element content of the 2 nd active material layer.

And step 3: same as in step 3 of comparative example 1.

Comparative example 4: single layer of doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the mixture is mixed, NMP (N-methyl pyrrolidone) is added, positive electrode slurry is obtained under the action of a vacuum mixer, wherein the solid content of the positive electrode slurry is 70-80 percent, the viscosity is 3500-6500 mPa.s, and the positive electrode slurry is coated on an aluminum foil with the thickness of 10 mu m by an extrusion coating machine according to an extrusion coating mode, so that the coating procedure is completed. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein, the total content of the first element Al and Mg is 8000 ppm; the total content of the second type of element S was 200ppm, the content of the first type of element was higher and the content of the second type of element was lower, relative to comparative example 5.

And 3, step 3: same as in step 3 of comparative example 1.

Comparative example 5: single layer of doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the mixture is mixed, NMP is added, positive electrode slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the positive electrode slurry is 70-80 percent, the viscosity is 3500-6500 mPa.s, and the positive electrode slurry is coated on an aluminum foil with the thickness of 10 mu m by an extrusion coating machine according to an extrusion coating mode, so that the coating procedure is completed. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein the total content of the first type elements Al and Mg is 1500 ppm; the total content of the second type of element S was 800ppm, the content of the first type of element was lower and the content of the second type of element was higher relative to comparative example 4.

And step 3: same as in step 3 of comparative example 1.

Example 1: double-layer doping modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

Wherein the total content of the first type elements Al and Mg in the 1 st active material layer is 1500ppm, and the total content of the second type elements S is 800 ppm; the total content of the first type elements Al and Mg of the 2 nd active material layer was 8000ppm, and the total content of the second type element S was 200 ppm. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 2 nd active material layer.

And step 3: same as in step 3 of comparative example 1.

Example 2: three-layer mixingHetero-modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: take the 1 st active material layer and the 3 rd active material layer as examples

Obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 3 rd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 3 rd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

and simultaneously coating all the active material layer slurry on an aluminum foil with the thickness of 10 mu m by using a three-layer coating machine, coating the 1 st active material layer slurry on the area closest to the aluminum foil, and coating the 3 rd active material layer slurry on the area farthest from the aluminum foil to finish the coating process. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein the total content of the first type elements Al and Mg in the 1 st active material layer is 1500ppm, and the total content of the second type elements S is 800 ppm; the total content of the first type elements Al and Mg of the 3 rd active material layer was 8000ppm, and the total content of the second type element S was 200 ppm. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 3 rd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 3 rd active material layer.

And step 3: same as in step 3 of comparative example 1.

Example 3: ten layers of doped modified active material

Step 1: same as in step 1 of comparative example 1.

Step 2: take the 1 st active material layer and the 10 th active material layer as examples

Obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry and NMP are mixed, and the 1 st active material layer slurry is obtained under the action of a vacuum mixer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 10 th active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 10 th active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

and simultaneously and sequentially coating all the active material layer slurry on an aluminum foil with the thickness of 10 mu m by adopting a coating machine, coating the active material layer slurry 1 in the area closest to the aluminum foil, and coating the active material layer slurry 10 in the area farthest from the aluminum foil to finish the coating process. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein the total content of the first type elements Al and Mg in the 1 st active material layer is 1500ppm, and the total content of the second type elements S is 800 ppm; the 10 th active material layer had a total content of the first type elements Al and Mg of 8000ppm and a total content of the second type element S of 200 ppm. Further, the content of the first type element of the 1 st active material layer is low relative to the content of the first type element of the 10 th active material layer, and the content of the second type element of the 1 st active material layer is high relative to the content of the second type element of the 10 th active material layer.

And step 3: same as in step 3 of comparative example 1.

Example 4: ten layers of doped modified active material

Step 1: same as in step 1 of comparative example 1.

Obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 5000ppm of Al, 1000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry and NMP are mixed, and the 1 st active material layer slurry is obtained under the action of a vacuum mixer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 10000ppm of Al, 4000ppm of Mg and 100ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 10 th active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 10 th active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

and simultaneously and sequentially coating all the active material layer slurry on an aluminum foil with the thickness of 10 microns by using a coating machine, coating the 1 st active material layer slurry on the area closest to the aluminum foil, and coating the 10 th active material layer slurry on the area farthest from the aluminum foil to finish the coating process. And drying, cold pressing and splitting to finish the preparation of the positive plate.

Wherein, the total content of the first type elements Al and Mg of the 1 st active material layer is 6000ppm, the maximum limit value of the first type element content of the active material layer closest to the anode current collector is reached, and the content of the second type element is 200ppm and lower; the 10 th active material layer had a total content of Al and Mg of the first type elements of 14000ppm, which reached the maximum limit of the content of the first type elements of the active material layer farthest from the positive electrode current collector, and a content of the second type elements of 100ppm, which was lower. Further, the content of the first type element of the 1 st active material layer is low relative to the content of the first type element of the 10 th active material layer, and the content of the second type element of the 1 st active material layer is high relative to the content of the second type element of the 10 th active material layer.

And 3, step 3: same as in step 3 of comparative example 1.

Example 5: ten layers of doped modified active material

Step 1: same as in step 1 of comparative example 1.

Obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 400ppm of Al, 100ppm of Mg and 1000ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and secondary particle NCM811 materials with 5000ppm of Al, 500ppm of Mg and 400ppm of S, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 10 th active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 10 th active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

Wherein the 1 st active material layer has a total content of Al and Mg of the first type elements of 500ppm reaching a minimum limit value of the content of the first type elements of the active material layer closest to the positive electrode current collector, and a content of the second type elements of 1000ppm reaching a maximum limit value of the content of the second type elements of the active material layer closest to the positive electrode current collector; the 10 th active material layer has a total content of Al and Mg of the first type element of 5500ppm, which reaches a minimum limit value of the content of the first type element of the active material layer farthest from the positive electrode current collector, and a content of the second type element of 400ppm, which reaches a maximum limit value of the content of the second type element of the active material layer farthest from the positive electrode current collector. Further, the content of the first type element of the 1 st active material layer is low relative to the content of the first type element of the 10 th active material layer, and the content of the second type element of the 1 st active material layer is high relative to the content of the second type element of the 10 th active material layer.

And step 3: same as in step 3 of comparative example 1.

Example 6: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 1500ppm of Al, 500ppm of Ti, 500ppm of F, 500ppm of S and 200ppm of Cl, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 7000ppm of Al content, 1000ppm of Ti content, 1500ppm of F content, 200ppm of S content and 100ppm of Cl content, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

Wherein the total content of the first type elements Al, Ti and F of the 1 st active material layer is 2500ppm, and the total content of the second type elements S and Cl is 700 ppm; the 2 nd active material layer had a total content of the first type elements Al, Ti and F of 9500ppm and a total content of the second type elements S and Cl of 300 ppm. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 2 nd active material layer.

And 3, step 3: same as in step 3 of comparative example 1.

Example 7: double-layer doped modified active material layer

Step 1: same as in comparative example 1, step 1.

Step 2: obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 1000ppm of Mg, 500ppm of Fe, 500ppm of B, 500ppm of S and 100ppm of Cu, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and a secondary particle NCM811 material with 5000ppm of Mg, 1500ppm of Fe, 1000ppm of B, 200ppm of S and 100ppm of Cu, and mixing the PVDF, the conductive carbon black and the secondary particle NCM811 material according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

Wherein the 1 st active material layer has a total content of the first type elements Mg, Fe and B of 2000ppm and a total content of the second type elements S and Cu of 600 ppm; the 2 nd active material layer had a total content of the first type elements Mg, Fe, and B of 7500ppm, and a total content of the second type elements S and Cu of 300 ppm. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 2 nd active material layer.

And step 3: same as in step 3 of comparative example 1.

Example 8: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black, and a secondary particle NCM811 material having a Mo content of 1000ppm, a Nb content of 500ppm, a W content of 500ppm, a Cl content of 200ppm, and a Ca content of 200ppm, and mixing the PVDF, the conductive carbon black, and the secondary particle NCM811 material in a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black, and a secondary particle NCM811 material having a Mo content of 4000ppm, a Nb content of 2000ppm, a W content of 2000ppm, a Cl content of 100ppm, and a Ca content of 100ppm, and mixing the PVDF, the conductive carbon black, and the secondary particle NCM811 material in a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

Wherein the total content of the first type elements Mo, Nb and W of the 1 st active material layer is 2000ppm, and the total content of the second type elements Cl and Ca is 400 ppm; the 2 nd active material layer had a total content of the first type elements Mo, Nb, and W of 8000ppm and a total content of the second type elements Cl and Ca of 200 ppm. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 2 nd active material layer.

And 3, step 3: same as in step 3 of comparative example 1.

Example 9: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: PVDF, conductive carbon black, and a secondary particle NCM811 material having an Al content of 1500ppm, a Zr content of 500ppm, an F content of 500ppm, an S content of 500ppm, and a Cl content of 200ppm were obtained, and the PVDF, the conductive carbon black, and the secondary particle NCM811 material were mixed in a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black, and a secondary particle NCM811 material having an Al content of 7000ppm, a Zr content of 1000ppm, an F content of 1500ppm, an S content of 200ppm, and a Cl content of 100ppm, wherein the PVDF, the conductive carbon black, and the secondary particle NCM811 material are mixed in a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

Wherein the 1 st active material layer has a total content of the first type elements Al, Zr and F of 2500ppm and a total content of the second type elements S and Cl of 700 ppm; the 2 nd active material layer had a total content of the first type elements Al, Zr, and F of 9500ppm and a total content of the second type elements S and Cl of 300 ppm. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 2 nd active material layer.

And 3, step 3: same as in step 3 of comparative example 1.

Example 10: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 1000ppm of Al, 500ppm of Mg and 800ppm of S, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry and NMP are mixed, and the 2 nd active material layer slurry is obtained under the action of a vacuum mixer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa.s;

and (3) simultaneously coating the 1 st active material layer slurry and the 2 nd active material layer slurry on an aluminum foil with the thickness of 10 microns by adopting a double-layer coating machine, coating the 1 st active material layer slurry on a region close to the aluminum foil, and coating the 2 nd active material layer slurry on a region far away from the aluminum foil to finish the coating process. And drying, cold pressing and splitting to finish the preparation of the positive plate.

And step 3: same as in step 3 of comparative example 1.

Example 11: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 400ppm of Al, 100ppm of Mg and 1000ppm of S, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 8000ppm of Al, 3000ppm of Mg, 3000ppm of Ti, 100ppm of S and 50ppm of Cl, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry and NMP are mixed, and the 2 nd active material layer slurry is obtained under the action of a vacuum mixer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa.s;

Wherein, the total content of the first type elements Al and Mg of the 1 st active material layer is 500ppm, the minimum limit value of the content of the first type elements of the active material layer closest to the anode current collector is reached, the total content of the second type elements S is 1000ppm, and the maximum limit value of the content of the second type elements of the active material layer closest to the anode current collector is reached; the total content of the first type elements Al, Mg and Ti of the 2 nd active material layer is 14000ppm, the maximum limit value of the content of the first type elements of the active material layer farthest from the positive electrode current collector is reached, and the total content of the second type elements S and Cl is 150ppm and lower. Further, the first type element content of the 1 st active material layer is lower relative to the first type element content of the 2 nd active material layer, and the second type element content of the 1 st active material layer is higher relative to the second type element content of the 2 nd active material layer.

And step 3: same as in step 3 of comparative example 1.

Example 12: double-layer doped modified active material layer

Step 1: same as in step 1 of comparative example 1.

Step 2: obtaining PVDF, conductive carbon black, and a NCM material in which single crystal particles and secondary particles having an Al content of 1000ppm, an Mg content of 500ppm, and an S content of 800ppm are mixed, and mixing the PVDF, the conductive carbon black, and the NCM material in which the single crystal particles and the secondary particles are mixed in a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 1 st active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 1 st active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

obtaining PVDF, conductive carbon black and single crystal particle NCM materials with 6000ppm of Al, 2000ppm of Mg and 200ppm of S, and mixing the PVDF, the conductive carbon black and the single crystal particle NCM materials according to a weight ratio of 1.4%: 1.1%: 97.5 percent of the active material layer slurry is mixed, NMP is added, and the 2 nd active material layer slurry is obtained under the action of a vacuum stirrer, wherein the solid content of the 2 nd active material layer slurry is 70-80 percent, and the viscosity is 3500-6500 mPa & s;

And step 3: same as in step 3 of comparative example 1.

For the above comparative examples 1 to 5 and examples 1 to 12, the average single ternary NCM single crystal grain was measured for the number of cracks, the mean mass energy density, the capacity retention rate, the cycle expansion rate, the 1h upper temperature limit, and other parameters after 500 cycles of 1.5C charge/1C discharge in an environment of 45 ℃, and the test results are shown in table 1.

The method for testing the number of cracks of the ternary NCM single crystal particles is described in the above, and will not be described herein again.

The method for testing the mass energy density mean value comprises the following steps: placing the battery cell in an environment with the temperature of 45 ℃, standing for 3h, discharging to 3V according to 1.5C when the battery cell reaches 45 ℃, and standing for 30 min; charging to cut-off current at constant voltage of 1.5 ℃, and standing for 30 min; repeating the above steps for 3 times, respectively measuring discharge energy of each time, and calculating average value E of discharge energy E of 3 times _everage (ii) a Measuring the mass M of the electric core by a weighing instrument, and calculating the mass energy density mean value PED, wherein PED is equal to E _everage /M。

The method for testing the capacity retention rate of 500 cycles at 45 ℃ comprises the following steps: placing the battery cell in an environment with the temperature of 45 ℃, standing for 3h, charging to 4.3V according to 1.5C when the battery cell reaches 45 ℃, then charging to 4.48V according to 0.7C, then charging to a cut-off current of 0.05C according to a constant voltage of 4.48V, then discharging to 3V according to 0.5C, and recording the initial capacity Q ₁ When the cycle reaches the required number, the previous discharge capacity is used as the capacity Q of the battery ₂ And calculating a capacity retention ratio (%) ═ Q ₂ /Q ₁ ×100％。

The method for testing the cyclic expansion rate after 500 cycles at 45 ℃ comprises the following steps: placing the battery core in an environment of 45 ℃, cleaning the surface of the battery core, discharging the battery core to a 0% SOC state, starting a press machine, slowly applying 5000N pressure and keeping the pressure, wherein the pressure application rate is 16N/s, and resetting the displacement value after keeping the pressure for 20 s; placing the battery core in a press, slowly applying 5000N pressure and keeping the pressure, wherein the pressure application rate is 14N/s, and measuring the thickness L of the battery after keeping the pressure for 26 s; and resetting the displacement value and keeping the pressure unchanged, performing charge-discharge circulation on the battery cell for 500 times, wherein the voltage of the charge-discharge circulation is 2-5V, continuously recording the thickness change value delta L in the charge-discharge circulation process to obtain a reversible expansion value, an irreversible expansion value and a charge expansion value, and calculating the expansion rate, wherein the expansion rate is delta L/L and 100%.

The method for testing the passing temperature upper limit for 1h of the hot box test after 500 cycles at 45 ℃ comprises the following steps: after the cell is circulated for 500 circles at 1C/1C45 ℃, stopping testing the cell, cooling the cell to room temperature, then fully charging the cell, carrying out 1h testing in hot boxes with different specified temperatures, and testing the cell at every 2-3 ℃ by using one step, wherein the cell has the highest temperature of no ignition and no combustion after being tested in the hot boxes.

TABLE 1 Performance parameters of the lithium ion batteries of examples and comparative examples

In the table, "-" indicates absence.

As can be seen from table 1, when comparing example 1 with comparative example 1, that is, comparing the double-layer doped modified active material layer structure defined in example 1 (i.e., the doped modified active material layer far from the positive electrode current collector is rich in the first element and short of the second element, and the doped modified active material layer near the positive electrode current collector is rich in the second element and short of the first element) with the single-layer doped modified active material layer structure relatively rich in the first element and short of the second element, although the capacity retention rate is slightly lost, the cycle expansion rate is slightly increased, and the upper temperature limit is slightly decreased, the mean mass-energy density is significantly increased, which is beneficial to improving the overall performance of the lithium ion battery.

Further, comparing example 1 with comparative example 2, that is, comparing the double-layer doped modified active material layer structure defined in example 1 (the same as above) with the single-layer doped modified active material layer structure relatively rich in the second element and lacking the first element, although the average value of the mass energy density is slightly lost, the capacity retention rate is obviously improved, the cycle expansion rate is obviously reduced, the passing temperature upper limit is also obviously improved, and the cycle performance of the lithium ion battery is favorably improved.

Further, comparing example 1 with comparative example 3, that is, comparing the double-layer doped modified active material layer structure defined in example 1 (the same as above) with the opposite double-layer doped modified active material layer structure (that is, the doped modified active material layer far from the positive electrode current collector is rich in the second type element and lacks the second type element, and the doped modified active material layer close to the positive electrode current collector is rich in the first type element and lacks the second type element), the capacity retention rate is obviously improved, the cycle expansion rate is obviously reduced, the upper limit of the passing temperature is also obviously improved, and the average value of the mass energy density is kept flat, so that the purpose of both high mass energy density and better cycle capacity can be achieved.

As can also be seen from table 1, in examples 2 to 5, the technical effects similar to those of example 1 can also be obtained by providing the doping modified active material layer in a three-layer, ten-layer structure.

As can also be seen from table 1, in examples 6 to 9, replacing the first type element with a combination of aluminum, titanium and fluorine, a combination of magnesium, iron and boron, a combination of molybdenum, niobium and tungsten, a combination of aluminum, zirconium and fluorine, or a combination of aluminum, magnesium and titanium, and replacing the second type element with a combination of sulfur and chlorine, a combination of sulfur and copper, or a combination of chlorine and calcium, also can achieve technical effects similar to those of example 1.

As can also be seen from table 1, comparing example 10 with comparative examples 4 and 5, respectively, replacing ternary NCM secondary particles with ternary NCM single crystal particles also achieves technical effects similar to example 1. Further, by comparing examples 12 and 10 and replacing the ternary NCM single-crystal particles with a mixture of ternary NCM single-crystal particles and secondary particles, a technical effect similar to that of example 10 can be obtained.

Further, by comparing examples 10 and 11, the number of cracks of the ternary NCM single crystal particles was adjusted within the range defined by formula (3), and the influence on the overall performance and cycle performance of the lithium ion battery was not significant, and the selection was flexible according to actual product requirements.

Those skilled in the art will appreciate that while some embodiments herein include some features included in other embodiments, rather than others, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims of the present invention, any of the claimed embodiments may be used in any combination.

In addition, the invention also provides a lithium ion battery, which comprises the positive plate in any one of the above embodiments.

In addition, the invention also provides an electric automobile which comprises the positive plate or the lithium ion battery in any one of the above embodiments.

So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.

Claims

1. A positive plate is characterized by comprising a positive current collector, wherein the positive current collector comprises a first side surface and a second side surface which are opposite, at least one of the first side surface and the second side surface is provided with N layers of doped modified active material layers, each layer of doped modified active material layer comprises an active material, and the active material is doped with a first element and a second element,

2. The positive electrode sheet according to claim 1, wherein the content of the first type of element doped in the i-th active material layer is less than the content of the first type of element doped in the i + 1-th active material layer;

3. The positive plate according to claim 2, wherein the first element is selected from at least one or more of titanium, magnesium, aluminum, iron, niobium, molybdenum, tungsten, fluorine and boron.

4. The positive electrode sheet according to claim 3, wherein the first type element is selected from a combination of aluminum and magnesium, a combination of aluminum, titanium and fluorine, a combination of magnesium, iron and boron, a combination of molybdenum, niobium and tungsten, a combination of aluminum, zirconium and fluorine, or a combination of aluminum, magnesium and titanium.

5. The positive electrode sheet according to claim 3 or 4, wherein the total content of the first type element doped in each of the active material layers satisfies the following formula:

((i-1)/(N-1))×5000+500≤P≤((i-1)/(N-1))×8000+6000

6. The positive electrode sheet according to claim 2, wherein the second type element is at least one or more selected from the group consisting of copper, calcium, sulfur and chlorine.

7. The positive electrode sheet according to claim 6, wherein the second type element is selected from sulfur, a combination of sulfur and chlorine, a combination of sulfur and copper, or a combination of chlorine and calcium.

8. The positive electrode sheet according to claim 6 or 7, wherein the total content of the second type element doped in each of the active material layers satisfies the following formula:

0＜Q≤1000-((i-1)/(N-1))×600

9. The positive electrode sheet according to any one of claims 1 to 4, wherein the active material is selected from a ternary NCM active material, a lithium iron phosphate active material, or a lithium-rich manganese-based active material.

10. The positive electrode sheet according to claim 9, wherein the active material is selected from ternary NCM active materials.