Battery cell, battery device, and electric device

Abstract

The application belongs to the technical field of batteries, and specifically discloses a battery monomer, a battery device and a power utilization device. The battery monomer comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer; the positive electrode film layer has a first surface away from the positive electrode current collector and a second surface arranged opposite to the first surface; the distance between the first surface and the second surface is H; along the stacking direction, the region formed from the second surface of the positive electrode film layer to the position at 0.1xH is recorded as the first region of the positive electrode film layer; along the stacking direction, the region formed from the first surface of the positive electrode film layer to the position at 0.1xH is recorded as the second region of the positive electrode film layer; the types of positive electrode active materials in the first region and the second region can be the same or different, and the positive electrode active materials in each region are matched with carbon nanotubes, so that the conductivity of the electrode sheet is improved to reduce the direct current resistance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a battery monomer, a battery device and a power consumption device. BACKGROUND

[0002] With the development of new energy technology, batteries are increasingly widely used, such as in mobile phones, notebook computers, electric cars, electric vehicles, energy storage devices, electric aircraft, electric ships, electric toy cars, electric toy ships, electric toy aircraft and electric tools. The requirements for battery performance are also increasing. SUMMARY

[0003] In view of the above problems, the present application provides a battery monomer, a battery device and a power consumption device, which improve the conductivity of the electrode sheet to reduce the direct current resistance of the battery.

[0004] In a first aspect, the present application provides a battery monomer, which comprises a positive electrode sheet and a negative electrode sheet stacked together.

[0005] The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector.

[0006] The positive electrode film layer has a first surface away from the positive electrode current collector and a second surface disposed opposite to the first surface.

[0007] The distance between the first surface and the second surface is H.

[0008] In the stacking direction of the electrode sheet, the region formed from the second surface of the positive electrode film layer to the position of 0.1xH is referred to as the first region of the positive electrode film layer.

[0009] In the stacking direction of the electrode sheet, the region formed from the first surface of the positive electrode film layer to the position of 0.1xH is referred to as the second region of the positive electrode film layer.

[0010] The first region comprises a first positive electrode active material and a first carbon nanotube, and the second region comprises a second positive electrode active material and a second carbon nanotube.

[0011] The first positive electrode active material comprises any one or more of lithium iron manganese phosphate and lithium manganese phosphate.

[0012] The second positive electrode active material comprises any one or more of lithium iron manganese phosphate and lithium iron phosphate.

[0013] The battery monomer provided by the present application is beneficial to improve the conductivity of the entire positive electrode sheet to reduce the direct current resistance of the battery, while also reducing the manganese leaching in the positive electrode film layer to improve the cycle or storage stability of the battery.

[0014] In some embodiments, the mass percentage content of the first carbon nanotubes in the first region is W1; the mass percentage content of the second carbon nanotubes in the second region is W2; W1≥W2.

[0015] In the present application, the mass percentage content of the first carbon nanotubes in the first region is W1; the mass percentage content of the second carbon nanotubes in the second region is W2; W1≥W2. Here, the mass percentage content is calculated by the amount of carbon nanotubes added during the preparation of the positive electrode film layer. Since the properties of carbon nanotubes in the positive electrode film layer are relatively stable, the loss is negligible. In fact, when taking high-magnification scanning electron microscope images of the positive electrode film layer, the content relationship between the two can be estimated according to the dispersion amount of the carbon nanotubes.

[0016] In some embodiments, the mass percentage content of the first carbon nanotubes in the first region is W1, which satisfies: 0

[0017] The mass percentage content of the second carbon nanotubes in the second region is W2, which satisfies: 0

[0018] The content of carbon nanotubes in the positive electrode film layer in the present application affects its conductivity. Generally speaking, the more the content, the stronger the conductivity. However, carbon nanotubes with high content are difficult to disperse during preparation, which may affect the conductivity. In the present application, W1 or W2 is independently selected from any value below 1% except zero, so as to further enhance the conductivity of the positive electrode active material under the premise of as much dispersion as possible.

[0019] In some embodiments, the first carbon nanotubes or the second carbon nanotubes each independently comprise any one or more of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0020] The single-walled carbon nanotubes in the present application refer to a single cylindrical layer of carbon atoms. The multi-walled carbon nanotubes in the present application refer to two or more layers of carbon atoms connected by intermolecular forces, or a single layer of carbon atoms wound around a cylindrical hollow core several times. The type of carbon nanotubes in the electrode plate is determined by high-power electron microscopy, and the average tube diameter of the carbon nanotubes is calculated by high-power electron microscopy to distinguish single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0021] In the present application, whether it is single-walled carbon nanotubes or multi-walled carbon nanotubes, since they all contain one-dimensional tubular structures, they can all exhibit good conductivity after being well dispersed in the positive electrode film layer.

[0022] In some embodiments, the first carbon nanotubes comprise single-walled carbon nanotubes; the single-walled carbon nanotubes satisfy any one or more of the following properties:

[0023] average tube length > 50 pm; aspect ratio 10-20; specific surface area 800 m 2 / g ~ 1600 m 2 / g.

[0024] In some embodiments, the above-mentioned second carbon nanotube includes a multi-walled carbon nanotube; the multi-walled carbon nanotube satisfies any one or more of the following properties:

[0025] average tube length 5 pm-50 pm; aspect ratio 1.2-2.0; specific surface area 170 m 2 / g ~ 220 m 2 / g.

[0026] The carbon nanotube of the present application has a one-dimensional tubular structure, and the tube diameter of the carbon nanotube refers to the outer diameter of the carbon nanotube. Generally speaking, the tube diameter of a single-walled carbon nanotube is smaller than that of a multi-walled carbon nanotube.

[0027] The tube length of the carbon nanotube of the present application refers to the value measured along the two ends of the one-dimensional tubular structure.

[0028] The aspect ratio of the carbon nanotube of the present application refers to the ratio between the tube length and the tube diameter of the carbon nanotube.

[0029] The specific surface area of the carbon nanotube in the present application is measured by a method known in the art, such as using a test instrument ASAP2460-physical adsorption analyzer, according to GB / T19587-2017: placing the carbon nanotube sample after drying and degassing treatment in liquid nitrogen, adjusting different test pressures, respectively measuring the adsorption amount of nitrogen, and drawing the adsorption and desorption isotherms, and calculating the specific surface area BET of the carbon nanotube according to the adsorption and desorption isotherms.

[0030] The present application can determine the type of carbon nanotubes in the positive plate by means of high-power electron microscope, and calculate the average tube length and aspect ratio of the carbon nanotube slurry by means of high-power electron microscope. In fact, when the carbon nanotubes of the present application are well dispersed in the positive film layer, the values of the tube length, aspect ratio and specific surface area BET of the carbon nanotubes change little and can be ignored.

[0031] The present application selects single-walled carbon nanotubes and multi-walled carbon nanotubes with the above-mentioned numerical ranges, which is beneficial for use with positive active materials to further improve the conductivity of the positive plate.

[0032] In some embodiments, the above-mentioned first positive active material includes any one or more of lithium iron manganese phosphate, lithium manganese phosphate;

[0033] The above-mentioned second positive active material includes lithium iron phosphate.

[0034] As described above, the conductivity of lithium iron phosphate is better than that of lithium manganese iron phosphate and lithium manganese phosphate, and the lithium iron phosphate does not contain manganese elements, so there is basically no phenomenon of manganese dissolution. The second positive electrode active material in the second area away from the positive electrode current collector has the conductivity equal to or stronger than that of the first positive electrode active material in the first area close to the positive electrode current collector, which is beneficial to improve the phenomenon of poor conductivity in the positive electrode film layer area away from the positive electrode current collector. At the same time, compared with the second positive electrode active material in the second area, the first positive electrode active material in the first area is used with equal or more amount of carbon nanotubes, which further improves the uniformity of the conductivity of the entire positive electrode sheet.

[0035] At the same time, due to the existence of the Jahn-Teller effect of manganese atoms in lithium manganese iron phosphate, the material structure is unstable, which leads to manganese dissolution and affects the cycle stability of the battery. To solve this problem, the design provided by the application is that the second positive electrode active material in the second area away from the positive electrode current collector includes lithium iron phosphate, and the lithium iron phosphate does not contain manganese elements, so there is basically no phenomenon of manganese dissolution, and the first positive electrode active material in the first area close to the positive electrode current collector includes any one or more of lithium manganese iron phosphate and lithium manganese phosphate. Since the first area close to the positive electrode current collector is more difficult to be fully soaked with electrolyte than the second area away from the positive electrode current collector, it is beneficial to reduce the probability of manganese dissolution of the first positive electrode active material in the first area close to the positive electrode current collector.

[0036] In some embodiments, the chemical formula of the above-mentioned lithium manganese iron phosphate is:

[0037] Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ;

[0038] N represents a lithium site doping element, and the lithium site doping element includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo and W;

[0039] M represents a manganese site and iron site doping element, and the manganese site and iron site doping element includes any one or more of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb and Nb;

[0040] Q represents a phosphorus site doping element, and the phosphorus site doping element includes any one or more of B, S, Si and N;

[0041] R represents an oxygen site doping element, the oxygen site doping element including any one or more of S, F, Cl, and Br;

[0042] a is 0.9 to 1.1;

[0043] b is 0 to 0.1;

[0044] x is 0.001 to 0.999;

[0045] y is 0.001 to 0.999;

[0046] 1-x-y is 0 to 0.1;

[0047] m is 0 to 0.1;

[0048] n is 0 to 0.1; the above-mentioned lithium iron manganese phosphate material is electrically neutral.

[0049] In some embodiments, the doping elements of the above-mentioned manganese sites and iron sites include any one or more of Al, Mg, and Ni;

[0050] 1-x-y is 0.01 to 0.1.

[0051] In some embodiments, the above-mentioned first positive electrode active material includes a first lithium iron manganese phosphate, and the molar percentage content of manganese elements in the first lithium iron manganese phosphate is Y1;

[0052] The above-mentioned second positive electrode active material includes a second lithium iron manganese phosphate, and the molar percentage content of manganese elements in the second lithium iron manganese phosphate is Y2;

[0053] Y1≥Y2;

[0054] The above-mentioned Y1 or Y2 is each independently selected from y×100%.

[0055] In some embodiments, the above-mentioned positive electrode film layer comprises a first sub-positive electrode film layer and a second sub-positive electrode film layer which are sequentially stacked;

[0056] The above-mentioned first sub-positive electrode film layer is located on at least one side surface of the positive electrode current collector;

[0057] The above-mentioned second sub-positive electrode film layer is located on a side surface of the first sub-positive electrode film layer away from the positive electrode current collector;

[0058] The above-mentioned first sub-positive electrode film layer comprises a first lithium iron manganese phosphate and a first carbon nanotube, the molar percentage content of manganese elements in the first lithium iron manganese phosphate is Y1, and 80%<Y1<100%; the mass percentage content of the first carbon nanotube in the first sub-positive electrode film layer is W1, and 0.5%<W1≤1%;

[0059] The second sub-cathode film layer contains second lithium manganese iron phosphate and second carbon nanotubes, the molar percentage content of manganese in the second lithium manganese iron phosphate is Y2, 0 < Y2 < 20%; the mass percentage content of the second carbon nanotubes in the second sub-cathode film layer is W2, 0 < W2 < 0.5%.

[0060] According to the above description, the second positive active material in the second area away from the positive current collector has stronger conductivity than the first positive active material in the first area close to the positive current collector, which is conducive to improving the poor conductivity in the area of the positive film layer away from the positive current collector. On this basis, the first positive active material in the first area is matched with a larger amount of carbon nanotubes than the second positive active material in the second area, which is conducive to further improving the uniform distribution of the electrical conductivity of the entire positive film layer to improve the conductivity of the pole piece and reduce the direct current resistance of the battery.

[0061] In some embodiments, the positive film layer comprises a first sub-cathode film layer, a third sub-cathode film layer and a second sub-cathode film layer stacked in sequence;

[0062] The first sub-cathode film layer is located on at least one side surface of the positive current collector;

[0063] The second sub-cathode film layer is located on the side surface of the first sub-cathode film layer away from the positive current collector;

[0064] The third sub-cathode film layer is located between the first sub-cathode film layer and the second sub-cathode film layer;

[0065] The first sub-cathode film layer contains first lithium manganese iron phosphate and first carbon nanotubes, the molar percentage content of manganese in the first lithium manganese iron phosphate is Y1, 60% < Y1 < 100%; the mass percentage content of the first carbon nanotubes in the first sub-cathode film layer is W1, 0.8% < W1 < 1%;

[0066] The third sub-cathode film layer contains third lithium manganese iron phosphate and third carbon nanotubes, the molar percentage content of manganese in the third lithium manganese iron phosphate is Y3, 20% < Y3 < 60%; the mass percentage content of the third carbon nanotubes in the third sub-cathode film layer is W3, 0.4 < W3 < 0.8%;

[0067] The second sub-cathode film layer contains second lithium manganese iron phosphate and second carbon nanotubes, the molar percentage content of manganese in the second lithium manganese iron phosphate is Y2, 0 < Y2 < 20%; the mass percentage content of the second carbon nanotubes in the second sub-cathode film layer is W2, 0 < W2 < 0.4%.

[0068] In some embodiments, the positive film layer further contains any one or more of carbon black and graphene.

[0069] The specific surface area of the carbon black is ≥100 m 2 / g;

[0070] and / or;

[0071] The number of layers of the graphene is 1-10 layers, and the average flake diameter of each layer is 2-8 μm;

[0072] and / or;

[0073] The mass percentage content of the carbon black and / or graphene in the positive electrode film layer is 0-2.5%.

[0074] The conductive agent in the positive electrode film layer in the present application can only contain carbon nanotubes with one-dimensional tubular structures, and can also contain one or both of carbon black and graphene, wherein the graphene has a sheet structure and the carbon black has a point structure. In some embodiments of the present application, the conductive agent is selected to be used in combination, such as one-dimensional tubular structure + sheet structure graphene + point carbon black, which is conducive to improving the conductivity of the positive electrode sheet by constructing a conductive network.

[0075] In some embodiments, the positive electrode film layer further comprises a dispersant, which comprises any one or more of hydrogenated nitrile rubber and modified compounds thereof, and polyvinylidene fluoride and modified compounds thereof;

[0076] The weight average molecular weight of the hydrogenated nitrile rubber and modified compounds thereof is 50,000-150,000;

[0077] and / or;

[0078] The hydrogenated nitrile rubber and modified compounds thereof comprise structural units derived from acrylonitrile monomers, and the mass percentage content of the structural units derived from acrylonitrile monomers in the hydrogenated nitrile rubber and modified compounds thereof is 20%-40%;

[0079] and / or;

[0080] The hydrogenation degree of the hydrogenated nitrile rubber and modified compounds thereof is ≥99%;

[0081] and / or;

[0082] The weight average molecular weight of the polyvinylidene fluoride and modified compounds thereof is 2 million-4 million;

[0083] and / or;

[0084] The crystallinity of the polyvinylidene fluoride and modified compounds thereof is 40%-60%.

[0085] The application uses carbon nanotubes as a conductive agent in the positive electrode film layer, but the one-dimensional tubular structure of the carbon nanotubes is easy to disperse badly and agglomerate, thereby affecting the conductivity. The application is good for dispersing the carbon nanotubes, and a certain type and content of dispersing agent is added.

[0086] In some embodiments, the film sheet resistance of the positive electrode tab is less than or equal to 1Ω.

[0087] In some embodiments, the film sheet resistance of the positive electrode tab is 0.1Ω-1Ω.

[0088] The film sheet resistance in the application can be used to measure the conductivity of the tab. The test of the film sheet resistance of the positive electrode tab in the application can be performed by a method known in the art, for example, a four-probe method, and a tab resistance meter test device of Yuaneng Technology. A 3*3mm small disc is cut from the positive electrode tab along the left, middle and right, and placed in the sample placement area of the resistance meter test device. The device is turned on to measure the resistance value.

[0089] In some embodiments, the particle size of the first positive electrode active material and / or the second positive electrode active material satisfies that Dv50 is 0.5μm-1.5μm.

[0090] In some embodiments, a carbon coating layer is formed on the outside of the particles of the first positive electrode active material and / or the second positive electrode active material, and the thickness of the carbon coating layer is 0.01μm-1μm.

[0091] In some embodiments, the distance H between the first surface and the second surface is 0.1mm-0.2mm.

[0092] The second aspect of the application is to provide a battery device comprising the secondary battery of the first aspect.

[0093] The third aspect of the application is to provide an electric device comprising the battery device of the second aspect.

[0094] The above description is only a summary of the technical solutions of the application. In order to more clearly understand the technical means of the application, the specific embodiments of the application can be implemented according to the content of the description, and in order to make the above and other purposes, characteristics and advantages of the application more obvious and easy to understand, the following specific embodiments of the application are described. BRIEF DESCRIPTION OF DRAWINGS

[0095] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered as limiting the application. Moreover, the same reference numerals are used to represent the same components throughout the drawings. In the drawings:

[0096] Figure 1 A schematic diagram of a battery structure for some embodiments of the present application;

[0097] Figure 2 A schematic diagram of an exploded structure of a battery for some embodiments of the present application;

[0098] Figure 3 A schematic diagram of a vehicle structure for some embodiments of the present application;

[0099] Figure 4 A schematic diagram of a battery pack structure for some embodiments of the present application;

[0100] Figure 5 A schematic diagram of a battery structure for some embodiments of the present application;

[0101] Figure 6 A schematic diagram of a positive electrode tab structure for some embodiments of the present application;

[0102] Figure 7 A schematic diagram of another positive electrode tab structure for some embodiments of the present application;

[0103] Figure 8 A schematic diagram of another positive electrode tab structure for some embodiments of the present application;

[0104] Reference signs in the detailed description of the embodiments are as follows:

[0105] 10000, vehicle;

[0106] 1000, battery; 2000, controller; 3000, motor;

[0107] 100, battery cell;

[0108] 200, box body; 210, first part; 220, second part;

[0109] 10, secondary battery;

[0110] 101, housing; 102, electrode assembly; 103, cover plate;

[0111] 1, negative electrode tab;

[0112] 2, positive electrode tab; 21, positive electrode current collector; 22, positive electrode film layer;

[0113] 3, separator film;

[0114] 22a, first surface; 22b, second surface;

[0115] 22A, first region; 22B, second region;

[0116] 222, first sub-positive electrode film layer;

[0117] 221、second sub-cathode film layer;

[0118] 223、third sub-cathode film layer.

[0119] Coordinate axis x direction: the stacking direction or thickness direction of the electrode tab;

[0120] Coordinate axis y direction: the length direction or width direction of the electrode tab. DETAILED DESCRIPTION

[0121] Hereinafter, specific embodiments of the battery cell, the battery device, and the power consuming device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0122] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing the arbitrary real number combinations between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0123] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0124] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0125] If not otherwise specified, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0126] If not otherwise specified, the terms "comprise" and "contain" mentioned in the present application mean open-ended, and can also mean closed-ended. For example, the terms "comprise" and "contain" can mean that other components not listed can also be included or contained, or can mean that only the listed components are included or contained.

[0127] If not otherwise specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions fulfills the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0128] If not otherwise specified, in the present application, the terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0129] If not otherwise specified, in the present application, the term "plurality" means more than two (including two), and similarly, "plurality of groups" means more than two groups (including two groups), and "plurality of pieces" means more than two pieces (including two pieces).

[0130] If not otherwise specified, in the present application, 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. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0131] Batteries have been widely used in various products due to their high energy density, long cycle life, safety and reliability, etc. In recent years, as the demand for batteries as energy sources has significantly increased, higher requirements have been placed on the performance of batteries such as conductivity.

[0132] Owing to their high safety, lithium iron phosphate, lithium manganese iron phosphate and lithium manganese phosphate positive electrode materials have gradually become the main positive electrode materials for electric vehicles or energy storage batteries. In particular, the charging voltage of lithium manganese iron phosphate can be increased from 3.4 V of lithium iron phosphate to 4.1 V. However, the electronic transmission capacity of lithium manganese iron phosphate is several orders of magnitude lower than that of lithium iron phosphate, resulting in relatively poor conductivity of lithium manganese iron phosphate materials.

[0133] To improve the conductivity of lithium manganese iron phosphate materials, the present application provides a battery monomer, a battery device and a power utilization device.

[0134] Firstly, the present application discloses a battery monomer, which comprises a positive electrode sheet and a negative electrode sheet arranged in a stack; the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector; the positive electrode film layer has a first surface away from the positive electrode current collector and a second surface arranged opposite to the first surface; the distance between the first surface and the second surface is H; along the stacking direction of the electrode sheet, the region formed from the second surface of the positive electrode film layer to the position of 0.1xH is referred to as the first region of the positive electrode film layer; along the stacking direction of the electrode sheet, the region formed from the first surface of the positive electrode film layer to the position of 0.1xH is referred to as the second region of the positive electrode film layer; the first region comprises a first positive electrode active material and a first carbon nanotube, and the second region comprises a second positive electrode active material and a second carbon nanotube; the first positive electrode active material comprises any one or more of lithium manganese iron phosphate and lithium manganese phosphate; and the second positive electrode active material comprises any one or more of lithium manganese iron phosphate and lithium iron phosphate.

[0135] The carbon nanotube in the present application has a one-dimensional tubular structure, which can well play the conductivity when used with the positive electrode active material, thereby improving the conductivity of the positive electrode sheet. At the same time, the design provided by the present application is beneficial to enhancing the conductivity of the second positive electrode active material in the second region away from the positive electrode current collector, reducing the difference in conductivity between the second region and the first region, and improving the phenomenon of poor conductivity in the region of the positive electrode film layer away from the positive electrode current collector, thereby making the electrical conductivity of the entire positive electrode film layer uniformly distributed in each region, so as to improve the conductivity of the electrode sheet and reduce the direct current resistance of the battery.

[0136] In addition, due to the Jahn-Teller effect of manganese atoms in the lithium manganese iron phosphate, the material structure is unstable, leading to manganese dissolution and affecting the cycle stability of the battery. To solve this problem, the design provided in the present application also makes the second positive electrode active material in the second area away from the positive electrode current collector include any one or more of lithium manganese iron phosphate and lithium iron phosphate, and the first positive electrode active material in the first area close to the positive electrode current collector includes any one or more of lithium manganese iron phosphate and lithium manganese phosphate, that is, the manganese content in the second area away from the positive electrode current collector is relatively lower. This design is conducive to reducing the manganese dissolution in the positive electrode film layer to improve the cycle or storage stability of the battery.

[0137] Therefore, the battery cell provided in the present application is conducive to improving the conductivity of the entire positive electrode sheet to reduce the direct current resistance of the battery, while also reducing the manganese dissolution in the positive electrode film layer to improve the cycle stability of the battery. Therefore, the design provided in the present application is conducive to improving the user experience.

[0138] Electrode assembly

[0139] The battery cell generally includes an electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet. During the charging and discharging process of the battery cell, active ions (such as lithium ions) are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, which can prevent the positive and negative electrodes from short-circuiting, and at the same time, the active ions can pass through.

[0140] Battery device

[0141] The battery apparatus mentioned in the embodiments of the present application can include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly can include a plurality of battery cells connected in series, in parallel, or in a mixed connection through a busbar component.

[0142] In some embodiments, the battery cell assembly is generally formed by arranging a plurality of battery cells.

[0143] As an example, the battery cell assembly can be a battery module formed by arranging and fixing a plurality of battery cells into an independent module. As an example, the battery module can be formed by bundling a plurality of battery cells with a cable tie.

[0144] In some embodiments, the battery device can be a battery pack, which includes a case and one or more battery cell assemblies housed in the case.

[0145] As an example, the battery cell assembly can be a battery module, which can be housed in the case by securing the battery module in the case.

[0146] As an example, the battery cell assembly can also be housed in the case by securing a plurality of battery cells directly in the case.

[0147] As an example, the case can include a first case and a second case. The first case and the second case are coupled such that an enclosed space is formed inside the case to receive the battery cell assembly. Enclosed here means covered or closed, which can be sealed or unsealed. The first case can be a top cover or a bottom plate.

[0148] As an example, the case can include a top cover, a frame, and a bottom plate. The top cover and the bottom plate are respectively connected to the frame such that an enclosed space is formed inside the case to receive the battery cell assembly.

[0149] In some embodiments, the case can be part of a chassis structure of a vehicle. For example, part of the case can be at least part of a floor of the vehicle, or part of the case can be at least part of a cross beam and a longitudinal beam of the vehicle.

[0150] The battery cell of the present application can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte composed of the above-mentioned battery cell. The outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, including but not limited to polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0151] The shape of the battery of the present application is not particularly limited, which can be cylindrical, square or any other shape. For example, Figure 1 is a square structure of the secondary battery 10 as an example.

[0152] According to some embodiments of the present application, with reference to Figure 2The outer package can include a shell 101 and a cover plate 103. The shell 101 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator film can form the electrode assembly 102 through a winding process or a stacking process. The electrode assembly 102 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 102. The number of electrode assemblies 102 contained in the secondary battery 10 can be one or more, and a person skilled in the art can select according to the actual needs.

[0153] The electrode assembly 102 provided by the application is applied to the secondary battery, which is beneficial to improve the performance of the secondary battery, and the secondary battery can be used as a power supply of an electric device or an energy storage unit of an electric device. The electric device is applied to the power field, for example, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited to the above-mentioned fields.

[0154] Some embodiments of the application take the electric device as a vehicle for example for convenience of description.

[0155] Please refer to Figure 3 , Figure 3 A structural schematic diagram of a vehicle 10000 provided by some embodiments of the application is shown. The vehicle 10000 can be a fuel automobile, a gas automobile or a new energy automobile, and the new energy automobile can be a pure electric vehicle, a hybrid electric vehicle or a range extended vehicle, etc. The vehicle 10000 is internally provided with a battery 1000, which can be arranged at the bottom, the head or the tail of the vehicle 10000. The battery 1000 can be used for power supply of the vehicle 10000, for example, the battery 1000 can be used as an operating power supply of the vehicle 10000. The vehicle 10000 can further include a controller 2000 and a motor 3000, and the controller 2000 is used to control the battery 1000 to supply power to the motor 3000, for example, to meet the working power demand of the vehicle 10000 during starting, navigation and driving.

[0156] In some embodiments of the application, the battery 1000 can not only be used as an operating power supply of the vehicle 10000, but also be used as a driving power supply of the vehicle 10000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 10000.

[0157] Please refer to Figure 4 , Figure 4An exploded view of a battery 1000 is provided for some embodiments of the present application. The battery 1000 includes a box 200 and a battery cell 100, a conventional battery cell includes a primary battery or a secondary battery, and the present application specifically protects a secondary battery 10, and the battery cell 100 is accommodated in the box 200. Among them, the box 200 is used to provide an accommodation space for the battery cell 100, and the box 200 can adopt various structures.

[0158] In some embodiments, the box 200 can include a first part 210 and a second part 220, the first part 210 and the second part 220 are mutually covered, and the first part 210 and the second part 220 jointly define an accommodation space for accommodating the secondary battery 100. The second part 220 can be a hollow structure with one end open, and the first part 210 can be a plate-shaped structure, the first part 210 covers the open side of the second part 220, so that the first part 210 and the second part 220 jointly define an accommodation space; the first part 210 and the second part 220 can also be hollow structures with one side open, and the open side of the first part 210 covers the open side of the second part 220. Of course, the box 200 formed by the first part 210 and the second part 220 can have various shapes, such as a cylinder, a cuboid, etc.

[0159] In the battery 1000, the battery cell 100 can be multiple, and the multiple battery cells 100 can be connected in series, in parallel, or in a mixed connection, where the mixed connection means that there are both series and parallel connections among the multiple battery cells 100. The multiple battery cells 100 can be directly connected in series, in parallel, or in a mixed connection, and then the whole of the multiple battery cells 100 is accommodated in the box 200; of course, the battery 1000 can also be that the multiple battery cells 100 are first connected in series, in parallel, or in a mixed connection to form a battery 1000 module, and then multiple battery 1000 modules are connected in series, in parallel, or in a mixed connection to form a whole, and are accommodated in the box 200. The battery 1000 can also include other structures, for example, the battery 1000 can also include a busbar component for realizing the electrical connection between the multiple battery cells 100.

[0160] Battery cell

[0161] This application discloses a battery cell in some embodiments, the battery cell including a positive electrode and a negative electrode stacked together; the positive electrode includes a positive current collector and a positive electrode film layer located on at least one side surface of the positive current collector; the positive electrode film layer has a first surface away from the positive current collector and a second surface disposed opposite to the first surface; the distance between the first surface and the second surface is H; the region formed along the stacking direction of the electrode, extending from the second surface of the positive electrode film layer to a position of 0.1×H, is denoted as the first region of the positive electrode film layer; the region formed along the stacking direction of the electrode, extending from the first surface of the positive electrode film layer to a position of 0.1×H, is denoted as the second region of the positive electrode film layer; the first region includes a first positive electrode active material and a first carbon nanotube, and the second region includes a second positive electrode active material and a second carbon nanotube; the first positive electrode active material includes any one or more of lithium manganese iron phosphate and lithium manganese phosphate; the second positive electrode active material includes any one or more of lithium manganese iron phosphate and lithium iron phosphate.

[0162] The positive electrode, separator, and negative electrode of this application can be formed into a secondary battery using winding or stacking processes. Specifically, this application... Figure 5 The diagram illustrates a secondary battery 10 formed using a stacking method, combined with... Figure 5 It is known that a negative electrode 1 or a positive electrode 2 is placed between two adjacent separators 3, and the negative electrode 1 and the positive electrode 2 are alternately arranged along the stacking direction (coordinate axis x direction). The number and size of the negative electrode 1 and / or the positive electrode 2 can be selected according to the actual situation, and will not be elaborated in this application. Furthermore, this application... Figure 5 The image only illustrates one type of lamination method; other lamination or winding methods are within the scope of protection of this application.

[0163] like Figure 6 The diagram illustrates that the positive electrode 2 includes a positive current collector 21 and a positive electrode film 22 located on at least one side surface of the positive current collector 21. Figure 6 The diagram illustrates a positive electrode film 22 disposed on either side of the surface of the positive electrode current collector 21. The positive electrode film 22 may also be located on both sides of the positive electrode current collector 21. The formation of the positive electrode film 22 on the surface of the positive electrode current collector 21 can be any method conventional in the art, such as coating, deposition, etc.

[0164] This application is in Figure 6 The diagram also illustrates the first surface 22a and the second surface 22b of the positive electrode film layer 22. The distance between the first surface 22a and the second surface 22b is H, which is the thickness of the positive electrode film layer 22 on one side of the positive electrode current collector. The measurement of this value H can be done in any way that is conventional in the art. In this application, it is measured using a micrometer.

[0165] For the convenience of describing the features of different regions in the positive electrode film layer, the region formed from the second surface 22b of the positive electrode film layer 22 to the 0.1xH position in the stacking direction of the tab is referred to as the first region 22A of the positive electrode film layer 22, and the region formed from the first surface 22a of the positive electrode film layer 22 to the 0.1xH position in the stacking direction of the tab is referred to as the second region 22B of the positive electrode film layer 22. The stacking direction of the tab also refers to the thickness direction of the tab, and in the following description, the stacking direction of the tab is also referred to as the thickness direction of the tab. Figure 6 In the above description, the x-axis direction is also referred to as the first region of the positive electrode film layer close to the positive electrode current collector, and the second region of the positive electrode film layer away from the positive electrode current collector. The 0.1xH position is only used to indicate the region, and the actual numerical range has no specific meaning.

[0166] The first region of the application includes the first positive electrode active material and the first carbon nanotube, and the second region includes the second positive electrode active material and the second carbon nanotube. The first positive electrode active material includes any one or more of lithium iron manganese phosphate and lithium manganese phosphate; and the second positive electrode active material includes any one or more of lithium iron manganese phosphate and lithium iron phosphate.

[0167] According to the above design idea and description, the positive electrode active material includes the following design methods:

[0168] (1) The first positive electrode active material includes lithium iron manganese phosphate, and the second positive electrode active material includes lithium iron manganese phosphate.

[0169] (2) The first positive electrode active material includes lithium iron manganese phosphate, and the second positive electrode active material includes lithium iron phosphate.

[0170] (3) The first positive electrode active material includes lithium manganese phosphate, and the second positive electrode active material includes lithium iron phosphate.

[0171] The above only lists some design methods, and in fact, the design method of containing two active materials in the first region and / or the second region is also within the protection scope of the application, which is not listed one by one here.

[0172] The carbon nanotube of the application is a one-dimensional tubular material mainly composed of sp 2 Hybrid carbon atoms, which has good electron mobility.

[0173] As described above, the conductivity of lithium manganese iron phosphate is lower than that of lithium iron phosphate by several orders of magnitude, resulting in relatively poor conductivity of lithium manganese iron phosphate material, and the conductivity of lithium manganese iron phosphate materials with different manganese contents is also different. Generally speaking, the conductivity of lithium manganese iron phosphate material with higher manganese content is weaker than that of lithium manganese iron phosphate material with lower manganese content. Therefore, the above-mentioned manner is adopted to reduce the difference between the conductivity of the second positive electrode active material in the second area away from the positive electrode current collector and the conductivity of the first positive electrode active material in the first area close to the positive electrode current collector, which is beneficial to improve the phenomenon of poor conductivity in the area of the positive electrode film layer away from the positive electrode current collector, and further makes the conductivity of the entire positive electrode film layer uniformly distributed in each area.

[0174] In addition, due to the existence of the Jahn-Teller effect of manganese atoms in lithium manganese iron phosphate, the material structure is unstable, which leads to manganese dissolution and further affects the cycle or storage stability of the battery. To solve this problem, the design method provided by the present application is adopted, that is, the second positive electrode active material in the second area away from the positive electrode current collector includes any one or more of lithium manganese iron phosphate and lithium iron phosphate, and the first positive electrode active material in the first area close to the positive electrode current collector includes any one or more of lithium manganese iron phosphate and lithium manganese phosphate. This design method is beneficial to reduce the manganese dissolution in the positive electrode film layer, so as to improve the cycle or storage stability of the battery.

[0175] Therefore, the battery cell provided by the present application is beneficial to improve the conductivity of the entire positive electrode sheet to reduce the direct current resistance of the battery, and at the same time, the manganese dissolution in the positive electrode film layer is also reduced to improve the cycle or storage stability of the battery.

[0176] In some embodiments, the mass percentage content of the first carbon nanotube in the first area is W1; the mass percentage content of the second carbon nanotube in the second area is W2; W1≥W2.

[0177] The mass percentage content of the first carbon nanotube in the first area in the present application is W1; the mass percentage content of the second carbon nanotube in the second area is W2; W1≥W2. Here, the mass percentage content is calculated by the amount of carbon nanotubes added during the preparation of the positive electrode film layer. Since the properties of carbon nanotubes in the positive electrode film layer are relatively stable, the loss is ignored. In fact, when taking a high-magnification scanning electron microscope image of the positive electrode film layer, the content relationship between the two can be estimated according to the dispersion amount of carbon nanotubes.

[0178] The present application selects the first positive electrode active material in the first area to use equal or more amount of carbon nanotubes with one-dimensional tubular structure compared with the second positive electrode active material in the second area, which is beneficial to further improve the uniform distribution of the conductivity of the entire positive electrode film layer in each area, so as to improve the conductivity of the electrode sheet to reduce the direct current resistance of the battery.

[0179] In some embodiments, the first carbon nanotube or the second carbon nanotube each independently comprises any one or more of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0180] The single-walled carbon nanotube of the present application refers to a single cylindrical layer of carbon atoms, and the multi-walled carbon nanotube of the present application refers to two or more layers of carbon atoms connected by intermolecular forces, or a single layer of carbon atoms wound several times around a cylindrical hollow core. The type of carbon nanotube in the electrode sheet is determined by means of a high-power electron microscope, and the average tube diameter of the carbon nanotube is calculated by means of a high-power electron microscope to further distinguish the single-walled carbon nanotube and the multi-walled carbon nanotube.

[0181] In the present application, whether it is a single-walled carbon nanotube or a multi-walled carbon nanotube, since it all contains a one-dimensional tubular structure, it can all play a good conductivity after being well dispersed in the positive electrode film layer.

[0182] In some embodiments, the mass percentage content of the first carbon nanotube in the first region is W1, which satisfies: 0 < W1≤ 1%;

[0183] The mass percentage content of the second carbon nanotube in the second region is W2, which satisfies: 0 < W2≤ 1%. In the present application, the content of carbon nanotubes in the positive electrode film layer affects its conductivity. Generally speaking, under the same type, the more the content, the stronger the conductivity, but the carbon nanotubes with high content are not easy to disperse during preparation, which will affect the conductivity. In the present application, W1 or W2 is each independently selected from any numerical value below 1% except for zero, so as to further enhance the conductivity of the positive electrode active material under the premise of as much dispersion as possible.

[0184] In these embodiments, the present application discloses that W1 or W2 each independently comprises any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or satisfies any one of the numerical range between any two of the above.

[0185] In some embodiments, the first carbon nanotube comprises single-walled carbon nanotubes; the single-walled carbon nanotubes satisfy any one or more of the following properties:

[0186] The average tube length is > 50 μm; the aspect ratio is 10-20; the specific surface area is 800 m 2 / g-1600 m 2 / g.

[0187] In some embodiments, the second carbon nanotube comprises multi-walled carbon nanotubes; the multi-walled carbon nanotubes satisfy any one or more of the following properties:

[0188] The average tube length is 5-50 μm; the aspect ratio is 1.2-2.0; the specific surface area is 170-220 m 2 / g-220 m 2 / g.

[0189] The carbon nanotubes of the present application have a one-dimensional tubular structure, and the tube diameter of the carbon nanotubes refers to the outer diameter of the carbon nanotubes. Generally, the tube diameter of single-walled carbon nanotubes is smaller than that of multi-walled carbon nanotubes.

[0190] The tube length of the carbon nanotubes of the present application refers to the value measured along the two ends of the one-dimensional tubular structure.

[0191] The aspect ratio of the carbon nanotubes of the present application refers to the ratio between the tube length and the tube diameter of the carbon nanotubes.

[0192] The specific surface area BET of the carbon nanotubes in the present application refers to the specific surface area determined by nitrogen adsorption according to the ASTM D 3663-78 standard based on the Brunauer-Emmett-Teller method described in the Journal of the American Chemical Society, 60, 309 (1938). The determination method of the specific surface area BET of the present application includes the known methods in the art, such as using the test instrument ASAP 2460-physical adsorption analyzer, and according to GB / T 19587-2017: placing the carbon nanotube sample after drying and degassing treatment in liquid nitrogen, adjusting different test pressures, respectively measuring the adsorption amount of nitrogen, and drawing the adsorption and desorption isotherms, and calculating the specific surface area BET of the carbon nanotubes according to the adsorption and desorption isotherms.

[0193] The present application can determine the carbon nanotubes in the positive plate by means of high-power electron microscopy, and calculate the average tube length and aspect ratio of the carbon nanotube slurry by means of high-power electron microscopy. In fact, when the carbon nanotubes of the present application are well dispersed in the positive film layer, the values of the tube length, aspect ratio and specific surface area BET of the carbon nanotubes change little and can be ignored.

[0194] The present application selects single-walled carbon nanotubes and multi-walled carbon nanotubes with the above numerical ranges, which is beneficial to be used with the positive active material to further improve the conductivity of the positive plate.

[0195] The present application discloses in these embodiments that the average tube length of the single-walled carbon nanotubes is greater than 50 μm and less than or equal to 100 μm. The present application specifically discloses that the average tube length of the single-walled carbon nanotubes is any one of 51 μm, 52 μm, 53 μm, 54 μm, 55 μm, 56 μm, 57 μm, 58 μm, 59 μm, 60 μm, 61 μm, 62 μm, 63 μm, 64 μm, 65 μm, 66 μm, 67 μm, 68 μm, 69 μm, 70 μm, 71 μm, 72 μm, 73 μm, 74 μm, 75 μm, 76 μm, 77 μm, 78 μm, 79 μm, 80 μm, 81 μm, 82 μm, 83 μm, 84 μm, 85 μm, 86 μm, 87 μm, 88 μm, 89 μm, 90 μm, 91 μm, 92 μm, 93 μm, 94 μm, 95 μm, 96 μm, 97 μm, 98 μm, 99 μm, 100 μm or any one in a numerical range between any two of the above.

[0196] The present application discloses in these embodiments that the aspect ratio of the single-walled carbon nanotubes is any one of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or any one in a numerical range between any two of the above.

[0197] The present application discloses in these embodiments that the specific surface area of the single-walled carbon nanotubes is any one of 800 m 2 / g, 850 m 2 / g, 900 m 2 / g, 950 m 2 / g, 1000 m 2 / g, 1050 m 2 / g, 1100 m 2 / g, 1150 m 2 / g, 1200 m 2 / g, 1250 m 2 / g, 1300 m 2 / g, 1350 m 2 / g, 1400 m 2 / g, 1450 m 2 / g, 1500 m 2 / g, 1550 m 2 / g, 1600 m 2 / g or any one in a numerical range between any two of the above.

[0198] The present application discloses in these embodiments that the average tube length of the multi-walled carbon nanotubes is any one of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm or any one in the numerical range between any two of the above.

[0199] The present application discloses in these embodiments that the aspect ratio of the multi-walled carbon nanotubes is any one of 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or any one in the numerical range between any two of the above.

[0200] The present application discloses in these embodiments that the specific surface area of the multi-walled carbon nanotubes is any one of 170 m 2 / g, 180 m 2 / g, 190 m 2 / g, 200 m 2 / g, 210 m 2 / g, 220 m 2 / g or any one in the numerical range between any two of the above.

[0201] In some embodiments, the first positive electrode active material described above includes any one or more of lithium iron manganese phosphate, lithium manganese phosphate; and the second positive electrode active material described above includes lithium iron phosphate.

[0202] As described above, the conductivity of lithium iron phosphate is better than that of lithium iron manganese phosphate and lithium manganese phosphate, and since the lithium iron phosphate does not contain manganese element, there is basically no phenomenon of manganese dissolution. The present application selects the second positive electrode active material in the second area away from the positive electrode current collector to have a conductivity equal to or stronger than that of the first positive electrode active material in the first area close to the positive electrode current collector, which is conducive to improving the phenomenon of poor conductivity in the positive electrode film layer area away from the positive electrode current collector. At the same time, the first positive electrode active material in the first area uses equal or more amount of carbon nanotubes than the second positive electrode active material in the second area, which further improves the uniformity of the conductivity of the entire positive electrode sheet.

[0203] Meanwhile, due to the Jahn-Teller effect of manganese atoms in the lithium manganese iron phosphate, the material structure is unstable, leading to manganese dissolution and affecting the cycle stability of the battery. To solve this problem, the design provided by the application is that the second positive electrode active material in the second area away from the positive electrode current collector includes lithium iron phosphate, and the lithium iron phosphate does not contain manganese elements, so there is basically no phenomenon of manganese dissolution, and the first positive electrode active material in the first area close to the positive electrode current collector includes any one or more of lithium manganese iron phosphate and lithium manganese phosphate; since the first area close to the positive electrode current collector is less likely to be fully soaked with electrolyte than the second area away from the positive electrode current collector, it is beneficial to reduce the probability of manganese dissolution of the first positive electrode active material in the first area close to the positive electrode current collector.

[0204] In some embodiments, the chemical formula of the above lithium manganese iron phosphate is:

[0205] Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ;

[0206] N represents a lithium site doping element, and the lithium site doping element includes any one or more of Zn, Al, Na, K, Mg, Nb, Mo and W;

[0207] M represents a manganese site and iron site doping element, and the manganese site and iron site doping element includes any one or more of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb and Nb;

[0208] Q represents a phosphorus site doping element, and the phosphorus site doping element includes any one or more of B, S, Si and N;

[0209] R represents an oxygen site doping element, and the oxygen site doping element includes any one or more of S, F, Cl and Br;

[0210] a is 0.9 to 1.1;

[0211] b is 0 to 0.1;

[0212] x is 0.001 to 0.999;

[0213] y is 0.001 to 0.999;

[0214] 1-x-y is 0 to 0.1;

[0215] m is 0 to 0.1;

[0216] n is 0 to 0.1; the above-mentioned manganese iron lithium phosphate material is electrically neutral.

[0217] The doping elements of the manganese site and the iron site in the present application are beneficial to improve the electronic conductivity of the material.

[0218] The above-mentioned b in the chemical formula in the present application is further 0.001 to 0.1.

[0219] The above-mentioned m in the chemical formula in the present application is further 0.001 to 0.1.

[0220] The above-mentioned n in the chemical formula in the present application is further 0.001 to 0.1.

[0221] The above-mentioned a in the chemical formula in the present application is any one of 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.05, 1.1 or any one satisfying a numerical range between any two of the above-mentioned in the embodiments.

[0222] The above-mentioned b in the chemical formula in the present application is any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or any one satisfying a numerical range between any two of the above-mentioned in the embodiments.

[0223] The above-mentioned x in the chemical formula in the present application is any one of 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99 or any one satisfying a numerical range between any two of the above-mentioned in the embodiments.

[0224] In these embodiments, the present application provides that y in the above formula is any one of 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any one of a range between any two of the above values.

[0225] In these embodiments, the present application provides that 1-x-y in the above formula is any one of 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any one of a range between any two of the above values.

[0226] In these embodiments, the present application provides that m in the above formula is any one of 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any one of a range between any two of the above values.

[0227] In these embodiments, the present application provides that n in the above formula is any one of 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any one of a range between any two of the above values.

[0228] In some embodiments, the doping elements of the manganese sites and the iron sites include any one or more of Al, Mg, and Ni.

[0229] 1-x-y is 0.01 to 0.1.

[0230] The selected lithium manganese iron phosphate in the present application further includes any one or more of Al, Mg, and Ni as doping elements, and the doping amount of the doping elements is controlled, which is beneficial to improve the electronic conductivity of the lithium manganese iron phosphate material, and further improve the conductivity of the positive electrode sheet.

[0231] In some embodiments, the first positive electrode active material comprises a first lithium iron manganese phosphate, and the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1;

[0232] The second positive electrode active material comprises a second lithium iron manganese phosphate, and the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2;

[0233] Y1≥Y2;

[0234] Y1 or Y2 is independently selected from y x 100%.

[0235] In the present application, the molar percentage content of manganese in lithium iron manganese phosphate refers to the molar percentage content of manganese in transition metal elements, and the calculation method of the numerical range corresponding to the definition given in the present application is that Y1 or Y2 is independently selected from y x 100%.

[0236] As mentioned above, due to the existence of the Jahn-Teller effect of manganese atoms in lithium iron manganese phosphate, the material structure is unstable, which leads to manganese dissolution and further affects the cycle stability of the battery, and the problem is more serious as the molar percentage content of manganese in lithium iron manganese phosphate is higher. The present application selects the molar percentage content of manganese in the first lithium iron manganese phosphate in the first area close to the positive electrode current collector to be greater than or equal to the molar percentage content of manganese in the second lithium iron manganese phosphate in the second area away from the positive electrode current collector. When the molar contents of the two are consistent, the use of carbon nanotubes with one-dimensional tubular structure is beneficial to improve the conductivity of the positive electrode plate. When the two have differences, it is obvious that the second positive electrode active material in the second area away from the positive electrode current collector has stronger conductivity than the first positive electrode active material in the first area close to the positive electrode current collector, which is beneficial to improve the phenomenon of poor conductivity in the positive electrode film area away from the positive electrode current collector. At the same time, compared with the second positive electrode active material in the second area, the first positive electrode active material in the first area uses equal or more amount of carbon nanotubes, which further improves the conductivity of the entire positive electrode plate. In addition, the second lithium iron manganese phosphate in the second area away from the positive electrode current collector is less likely to have manganese dissolution than the first lithium iron manganese phosphate in the first area close to the positive electrode current collector, and the first lithium iron manganese phosphate in the first area close to the positive electrode current collector is less likely to be fully infiltrated with electrolyte, so both are beneficial to reduce the probability of manganese dissolution.

[0237] In some embodiments, the positive electrode film layer comprises a first sub-positive electrode film layer and a second sub-positive electrode film layer stacked in sequence; the first sub-positive electrode film layer is located on at least one side surface of the positive electrode current collector; the second sub-positive electrode film layer is located on the side surface of the first sub-positive electrode film layer away from the positive electrode current collector; the first sub-positive electrode film layer comprises first lithium iron manganese phosphate and first carbon nanotubes, the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1, 80% < Y1 < 100%; the mass percentage content of the first carbon nanotubes in the first sub-positive electrode film layer is W1, 0.5% < W1 ≤ 1%;

[0238] The second sub-positive electrode film layer comprises second lithium iron manganese phosphate and second carbon nanotubes, the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2, 0 < Y2 ≤ 20%; the mass percentage content of the second carbon nanotubes in the second sub-positive electrode film layer is W2, 0 < W2 ≤ 0.5%.

[0239] As Figure 7 described above, the positive electrode film layer 22 of the present application comprises a first sub-positive electrode film layer 222 and a second sub-positive electrode film layer 221, the molar percentage content of manganese in the first lithium iron manganese phosphate of the first sub-positive electrode film layer 222 is greater than the molar percentage content of manganese in the second lithium iron manganese phosphate of the second sub-positive electrode film layer 221, specifically the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1, which satisfies: 80% < Y1 < 100%, the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2, 0 < Y2 ≤ 20%; according to the above description, the second positive electrode active material in the second region away from the positive electrode current collector has stronger conductivity than the first positive electrode active material in the first region close to the positive electrode current collector, which is beneficial to improve the phenomenon of poor conductivity in the region of the positive electrode film layer away from the positive electrode current collector. On this basis, the first positive electrode active material in the first region uses more amount of carbon nanotubes than the second positive electrode active material in the second region, which is beneficial to further improve the uniform distribution of the electrical conductivity of the entire positive electrode film layer, so as to improve the conductivity of the electrode sheet and reduce the direct current resistance of the battery.

[0240] The molar percentage content of manganese in the lithium iron manganese phosphate and the mass percentage content of carbon nanotubes in each sub-positive electrode film layer given herein are characteristics possessed by the raw materials used in the preparation of the positive electrode film layer or calculated or converted after reasonable control, and the loss or change is ignored.

[0241] The present application gives the molar percentage content of the manganese element in the first lithium iron manganese phosphate as Y1 is any one of 80.5%, 81%, 81.5%, 82%, 82.5%, 83%, 83.5%, 84%, 84.5%, 85%, 85.5%, 86%, 86.5%, 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.99% or any one in the numerical range between any two of the above.

[0242] The present application gives the molar percentage content of the manganese element in the second lithium iron manganese phosphate as Y2 is any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 13.5%, 14.0%, 14.5%, 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5%, 19.6%, 19.7%, 19.8%, 19.9% or any one in the numerical range between any two of the above.

[0243] The present application gives the mass percentage content of the first carbon nanotube in the first sub-cathode film layer as W1 is any one of 0.51%, 0.52%, 0.53%, 0.54%, 0.55%, 0.56%, 0.57%, 0.58%, 0.59%, 0.60%, 0.61%, 0.62%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 0.96%, 0.97%, 0.98%, 0.99% or any one in the numerical range between any two of the above.

[0244] The application gives the mass percentage content of the second carbon nanotube in the second sub-cathode film layer as W2 in these embodiments as any one of 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49% or any one of a numerical range between any two of the above.

[0245] In some embodiments, the above-mentioned cathode film layer comprises a first sub-cathode film layer, a third sub-cathode film layer and a second sub-cathode film layer stacked in sequence; the first sub-cathode film layer is located on at least one side surface of the above-mentioned cathode current collector; the second sub-cathode film layer is located on the side surface of the above-mentioned first sub-cathode film layer away from the above-mentioned cathode current collector; the third sub-cathode film layer is located between the above-mentioned first sub-cathode film layer and the above-mentioned second sub-cathode film layer; the first sub-cathode film layer comprises first lithium iron manganese phosphate and first carbon nanotubes, the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1, 60% < Y1 < 100%; the mass percentage content of the first carbon nanotube in the first sub-cathode film layer is W1, 0.8% < W1 ≤ 1%; the third sub-cathode film layer comprises third lithium iron manganese phosphate and third carbon nanotubes, the molar percentage content of manganese in the third lithium iron manganese phosphate is Y3, 20% < Y3 ≤ 60%; the mass percentage content of the third carbon nanotube in the third sub-cathode film layer is W3, 0.4 < W3 ≤ 0.8%; the second sub-cathode film layer comprises second lithium iron manganese phosphate and second carbon nanotubes, the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2, 0 < Y2 ≤ 20%; the mass percentage content of the second carbon nanotube in the second sub-cathode film layer is W2, 0 < W2 ≤ 0.4%.

[0246] As Figure 8 The cathode film layer 22 of the application comprises a first sub-cathode film layer 222, a third sub-cathode film layer 223 and a second sub-cathode film layer 221, and along the direction of the electrode sheet stacking (the coordinate axis x direction), the molar percentage content of manganese in the lithium iron manganese phosphate gradually changes in sequence, and similarly, the mass percentage content of the carbon nanotube also gradually changes in sequence. This design is beneficial in improving the uniform distribution of the electrical conductivity of the entire cathode film layer in each region, improving the conductivity of the electrode sheet and reducing the direct current resistance of the battery, and on the other hand, the second region away from the cathode current collector is less likely to cause manganese leaching compared to the first region close to the cathode current collector, thereby improving the cycle or storage stability of the battery.

[0247] The present application gives the molar percentage content of manganese element in the first lithium iron manganese phosphate in these embodiments Y1 is any one of 60.1%, 60.5%, 61.0%, 61.1%, 61.5%, 62.0%, 62.1%, 62.5%, 63.0%, 63.1%, 63.5%, 64.0%, 64.1%, 64.5%, 65.0%, 65.1%, 65.5%, 66.0%, 66.1%, 66.5%, 67.0%, 67.5%, 68.0%, 68.5%, 69.0%, 69.5%, 70.0%, 70.5%, 71.0%, 71.5%, 72.0%, 72.5%, 73.0%, 73.5%, 74.0%, 74.5%, 75.0%, 75.5%, 76.0%, 76.5%, 77.0%, 77.5%, 78.0%, 78.5%, 79.0%, 79.5%, 80.0%, 80.5%, 81.0%, 81.5%, 82.0%, 82.5%, 83.0%, 83.5%, 84%, 84.5%, 85%, 85.5%, 86%, 86.5%, 87%, 87.5%, 88%, 88.5%, 89%, 89.5%, 90%, 90.5%, 91%, 91.5%, 92%, 92.5%, 93%, 93.5%, 94%, 94.5%, 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.99% or any one in the numerical range between any two of the above.

[0248] The present application gives the molar percentage content of the manganese element in the third lithium iron manganese phosphate as Y3 is any one of 20.1%, 20.5%, 21.0%, 21.5%, 22.0%, 22.5%, 23.0%, 23.5%, 24.0%, 24.5%, 25.0%, 25.5%, 26.0%, 26.5%, 27.0%, 27.5%, 28.0%, 28.5%, 29.0%, 29.5%, 30.0%, 30.5%, 31.0%, 31.5%, 32.0%, 32.5%, 33.0%, 33.5%, 34.0%, 34.5%, 35.0%, 35.5%, 36.0%, 36.5%, 37.0%, 37.5%, 38.0%, 38.5%, 39.0%, 39.5%, 40.0%, 40.5%, 41.0%, 41.5%, 42.0%, 42.5%, 43.9%, 43.5%, 44.0%, 44.5%, 45.0%, 45.5%, 46.0%, 46.5%, 47.0%, 47.5%, 48.0%, 48.5%, 49.0%, 49.5%, 50.0%, 50.5%, 51.0%, 51.5%, 52.0%, 52.5%, 53.0%, 53.5%, 54.0%, 54.5%, 54.5%, 55.0%, 55.5%, 56.0%, 56.5%, 57.0%, 57.5%, 58.0%, 58.5%, 59.0%, 59.5%, 59.9% or any one in the numerical range between any two of the above.

[0249] The present application gives the molar percentage content of the manganese element in the second lithium iron manganese phosphate as Y2 is any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5%, 11.0%, 11.5%, 12.0%, 12.5%, 13.0%, 13.5%, 14.0%, 14.5%, 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5%, 19.6%, 19.7%, 19.8%, 19.9% or any one in the numerical range between any two of the above.

[0250] In the embodiments, the first carbon nanotube has a mass percentage content of W1 of any one of 0.81%, 0.85%, 0.90%, 0.95%, 0.96%, 0.97%, 0.98%, 0.99% or any one of the ranges between any two of the above values.

[0251] In the embodiments, the third carbon nanotube has a mass percentage content of W3 of any one of 0.41%, 0.45%, 0.50%, 0.51%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80% or any one of the ranges between any two of the above values.

[0252] In the embodiments, the second carbon nanotube has a mass percentage content of W2 of any one of 0.01%, 0.05%, 0.1%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40% or any one of the ranges between any two of the above values.

[0253] In some embodiments, the positive electrode film layer further comprises any one or more of carbon black and graphene;

[0254] The specific surface area of the carbon black is ≥100 m 2 / g.

[0255] In some embodiments, the graphene has a layer number of 1-10 layers, and each layer has an average flake diameter of 2-8 μm.

[0256] In some embodiments, the mass percentage content of the carbon black and / or graphene in the positive electrode film layer is 0-2.5%.

[0257] The graphene of the present application is a single-layer carbon nanomaterial composed of sp 2 hybridized carbon atoms, has a flake structure and good electron mobility.

[0258] The graphene flake structure of the present application can be a single flake or a plurality of flakes stacked together. The measurement method of the number of graphene layers includes any method in the art, for example, the transmission electron microscopy + electron diffraction method can be selected to determine the number of layers in the application area to be measured. The number of layers of the sample is determined by changing the direction of the electron beam incident on the graphene and observing the change in the intensity of the diffraction spot of the graphene at different electron beam incident angles.

[0259] The flake diameter of each layer of the present application refers to the lateral dimension of the graphene flake structure, wherein the average flake diameter is the mean value of the statistical flake diameter of each layer, which is observed by high-power electron microscope and obtained by measurement. The mean value measurement method herein is any conventional method in the art.

[0260] The average flake diameter of the graphene of the present application is 2 μm to 8 μm, so as to facilitate the coating on the partial surface of the positive electrode active material and directly improve the conductivity of the positive electrode active material.

[0261] The present application discloses in these embodiments that the average flake diameter of each layer is any one of 2 μm, 2.5 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 7.8 μm or any one of the above-mentioned ranges.

[0262] The definition and measurement method of the specific surface area of the carbon black of the present application are consistent with the above-mentioned carbon nanotubes, which are not repeated herein.

[0263] The large specific surface area of the carbon black of the present application is also conducive to increasing the contact between the carbon black and the positive electrode active material, and further improving the conductivity of the positive electrode sheet.

[0264] In some embodiments, the specific surface area BET of the carbon black is 100 m 2 / g to 1000 m 2 / g.

[0265] The present application gives in these embodiments that the specific surface area BET of the carbon black is 100 m 2 / g to 150 m 2 / g, 120 m 2 / g to 180 m 2 / g, 150 m 2 / g to 250 m 2 / g, 180 m 2 / g to 300 m 2 / g, 250 m 2 / g to 400 m 2 / g, 300 m 2 / g to 450 m 2 / g, 400 m 2 / g to 500 m 2 / g, 450 m 2 / g to 550 m 2 / g, 500 m 2 / g to 600 m 2 / g, 550 m 2 / g to 700 m 2 / g, 600 m 2 / g to 800 m 2 / g, 650 m 2 / g ~ 1000 m 2 / g or any of the above-mentioned range values satisfying any two.

[0266] The conductive agent in the positive electrode film layer in the present application can only contain carbon nanotubes with one-dimensional tubular structure, and can also contain one or both of carbon black and graphene, wherein graphene has a sheet structure and carbon black has a point structure. In some embodiments of the present application, the conductive agent is selected to be used in combination, such as one-dimensional tubular structure + sheet structure graphene + point carbon black, which is conducive to improving the conductivity of the positive electrode sheet by constructing a conductive network.

[0267] In some embodiments of the present application, the mass percentage content of carbon black in the above-mentioned positive electrode film layer is 0-2.5%.

[0268] In some embodiments of the present application, the mass percentage content of graphene in the above-mentioned positive electrode film layer is 0-2.5%.

[0269] In some embodiments of the present application, the total mass percentage content of carbon black and graphene in the above-mentioned positive electrode film layer is 0-2.5%.

[0270] In these embodiments of the present application, the mass percentage content of each component or the total amount in the positive electrode film layer is any one of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5% or any of the above-mentioned range values satisfying any two.

[0271] In some embodiments, the above-mentioned positive electrode film layer further comprises a dispersant, which comprises any one or more of hydrogenated nitrile rubber and its modified compounds, polyvinylidene fluoride and its modified compounds;

[0272] The weight average molecular weight of the above-mentioned hydrogenated nitrile rubber and its modified compounds is 50,000-150,000.

[0273] In some embodiments, the above-mentioned hydrogenated nitrile rubber and its modified compounds contain structural units derived from acrylonitrile monomers, and the mass percentage content of the structural units derived from acrylonitrile monomers in the above-mentioned hydrogenated nitrile rubber and its modified compounds is 20%-40%.

[0274] In some embodiments, the hydrogenation degree of the above-mentioned hydrogenated nitrile rubber and its modified compounds is ≥99%.

[0275] In some embodiments, the weight average molecular weight of the above-mentioned polyvinylidene fluoride and its modified compounds is 2 million-4 million.

[0276] In some embodiments, the crystallinity of the above-mentioned polyvinylidene fluoride and modified compounds thereof is 40% to 60%.

[0277] The present application uses carbon nanotubes as a conductive agent in the positive electrode film layer, but the one-dimensional tubular structure of carbon nanotubes is prone to poor dispersion and agglomeration, which in turn affects the development of conductivity. The present application is to disperse the carbon nanotubes well by selecting and adding a certain type and content of dispersing agent.

[0278] The hydrogenated nitrile rubber of the present application is a product obtained by hydrogenating and saturating the carbon-carbon double bonds on the molecular chain of nitrile rubber, and the nitrile rubber is a polymer obtained by polymerization of acrylonitrile and butadiene monomers. The present application refers to a collection of macromolecules that are chemically uniform but differ in degree of polymerization, molar mass and chain length, which are prepared by polymerization reaction. The modified compounds of hydrogenated nitrile rubber in the present application generally refer to compounds prepared by chemical modification, such as functional group modification of hydrogenated nitrile rubber, which includes but is not limited to carboxyl, ester, amide, etc. The hydrogenated nitrile rubber and its modified compounds provided by the present application improve the dispersibility of carbon nanotubes to increase the content of conductive agent in the positive electrode film layer, thereby developing good conductivity.

[0279] The determination method of the weight average molecular weight of the hydrogenated nitrile rubber and its modified compounds of the present application includes conventional methods in the art, such as gel chromatography.

[0280] The hydrogenated nitrile rubber and its modified compounds with appropriate weight average molecular weight in the present application are beneficial to develop their good dispersing ability.

[0281] The present application discloses in these embodiments that the weight average molecular weight of the hydrogenated nitrile rubber and its modified compounds includes any one or more of 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, 80,000, 85,000, 90,000, 95,000, 100,000, 105,000, 110,000, 112,000, 115,000, 120,000, 125,000, 130,000, 135,000, 140,000, 145,000, 150,000.

[0282] In some embodiments, the above-mentioned hydrogenated nitrile rubber and its modified compounds contain structural units derived from acrylonitrile monomers, and the mass percentage content of the structural units derived from acrylonitrile monomers is 20% to 40%.

[0283] The hydrogenated nitrile rubber of the present application is obtained by further hydrogenating the carbon-carbon double bonds of the polymer obtained by polymerization of acrylonitrile and butadiene monomers. The modified compound of the hydrogenated nitrile rubber generally refers to a mixture prepared by chemical modification, such as functional group modification of the hydrogenated nitrile rubber, and the functional groups include but are not limited to carboxyl, ester, amide, etc. As described above, after qualitative and quantitative testing of the hydrogenated nitrile rubber and its modified compound in the pole piece, the mass percentage content of acrylonitrile can be conveniently calculated.

[0284] The present application discloses that the mass percentage content of acrylonitrile in the hydrogenated nitrile rubber and its modified compound in these embodiments includes any one or more of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%.

[0285] In some embodiments, the hydrogenation degree of the hydrogenated nitrile rubber and its modified compound described above is ≥ 99%.

[0286] The hydrogenated nitrile rubber of the present application is obtained by further hydrogenating the carbon-carbon double bonds of the polymer obtained by polymerization of acrylonitrile and butadiene monomers, so the hydrogenation degree here also refers to the hydrogenation saturation degree, and the determination method includes measuring the residual double bonds by infrared spectrometer, etc., and calculating the double bond content, so the hydrogenation degree is (100%-double bond content). Or determined by nuclear magnetic resonance hydrogen spectrometer.

[0287] The hydrogenation degree of the hydrogenated nitrile rubber and its modified compound in the present application is relatively high, and the flexibility of the molecule is also better, and the dispersibility of the carbon nanotube is also better.

[0288] The polyvinylidene fluoride of the present application includes structural units derived from vinylidene fluoride, and the polyvinylidene fluoride and its modified compound of the present application include other structural units in addition to the structural units derived from vinylidene fluoride, including but not limited to acrylic monomer structural units.

[0289] The test of the weight average molecular weight of the polyvinylidene fluoride and modified compounds in the present application can be performed by using the method known in the art, for example, by using a gel chromatography, such as Waters 2695 Isocratic HPLC type gel chromatograph (differential refractive detector 2141). In some embodiments, the test method is to use a polystyrene solution sample of a certain mass fraction as a reference, and a matching chromatographic column (oil: Styragel HT5 DMF 7.8*300 mm + Styragel HT4) is selected. A certain mass fraction of polyvinylidene fluoride and modified compound glue solution is prepared with purified N-methyl pyrrolidone (NMP) solvent, and the prepared solution is placed for one day for standby. During the test, the syringe is first used to suck tetrahydrofuran for flushing several times. Then 5 ml of experimental solution is sucked, the air in the syringe is excluded, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the sample port. After the reading is stable, the data is obtained, and the weight average molecular weight is read.

[0290] The polyvinylidene fluoride and modified compounds with a weight average molecular weight of 2 million to 4 million are selected as the dispersant for dispersing carbon nanotubes in the present application, which is beneficial to improve the dispersibility.

[0291] In the present application, the weight average molecular weight of the polyvinylidene fluoride and modified compounds in these embodiments is any one of 2 million, 2.5 million, 3 million, 3.5 million, 4 million or any one of the above-mentioned ranges.

[0292] The crystallinity of the polyvinylidene fluoride and modified compounds in the present application refers to the proportion of the crystalline region in the compound. There are some regions with stable and regular arrangement of molecules in the microstructure, and the region with regular and compact arrangement of molecules is called the crystalline region.

[0293] In the present application, the test of the crystallinity can be performed by using the method known in the art, such as by using differential scanning calorimetry. In some embodiments, 0.5 g of polyvinylidene fluoride and modified compounds is placed in an aluminum pan, leveled, covered with a crucible cover, and tested under a nitrogen atmosphere at a purging gas of 50 ml / min, a protective gas of 70 mL / min, a heating rate of 8 ℃ / min, a test temperature range of 30 ℃-200 ℃, using a differential scanning calorimeter (DSC) of DSC 200F30 type from Netzsch Company, Germany, to eliminate the thermal history.

[0294] The test will obtain the DSC / (Mw / mg) of the polyvinylidene fluoride and modified compound thereof as a function of temperature, and the integral is performed, and the peak area is the melting enthalpy ΔH (J / g) of the polyvinylidene fluoride and modified compound thereof, the crystallinity = ΔH / (ΔHm100%) * 100%, wherein ΔHm100% is the standard melting enthalpy (crystalline heat of fusion) of the compound, ΔHm100% = 104.7 J / g.

[0295] The compound with the crystallinity in the above range can improve the dispersion of the carbon nanotubes at a low addition amount and reduce the battery impedance.

[0296] In these embodiments, the present application provides the polyvinylidene fluoride and modified compound thereof with a crystallinity of any one of 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, or any one of the ranges of any two of the above.

[0297] In some embodiments, the above positive electrode tab has a sheet resistance of 1Ω or less.

[0298] In some embodiments, the above positive electrode tab has a sheet resistance of 0.1Ω to 1Ω.

[0299] The sheet resistance in the present application can be used to measure the conductivity of the tab, and the test of the sheet resistance of the positive electrode tab in the present application can be tested by a method known in the art, for example, by using a four-probe method, and by using a Yuankang Technology tab resistance tester device, cutting a 3*3mm small disc from the left, middle and right of the positive electrode tab, and placing it in the sample placement area of the resistance tester device, and then turning on the device to measure the resistance value.

[0300] In some embodiments, the particle size of the first positive electrode active material and / or the second positive electrode active material satisfies that the Dv50 is 0.5μm to 1.5μm.

[0301] In some embodiments, a carbon coating layer is formed on the outside of the particles of the first positive electrode active material and / or the second positive electrode active material, and the thickness of the carbon coating layer is 0.01μm to 1μm.

[0302] The particle size Dv50 in the present application contains 50% of the particle volume larger than it and 50% of the particle volume smaller than it, also known as the median diameter, which is usually used to represent the average particle size. The volume particle size distribution in the present application can be measured by conventional methods in the art, such as using a particle size analyzer to determine the particle size distribution and then obtaining it by statistics. In these embodiments, the particle size distribution is determined by laser diffraction particle size analysis method, and the particle size distribution graph is obtained according to the standard GB / T19077-2016, and then the particle size distribution is obtained by calculation.

[0303] In these embodiments, the particle size of the first positive electrode active material and / or the second positive electrode active material is any one of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or any one of the above-mentioned range values.

[0304] The carbon coating layer in the present application refers to a substance formed on the outer surface of the positive electrode active material. The carbon coating layer can completely or partially coat the outer surface of the positive electrode active material. Since the carbon coating layer has electrical conductivity, on the one hand, the carbon coating layer is beneficial to improve the electrical conductivity of the positive electrode active material, and on the other hand, the carbon coating layer can partially block the reaction probability of manganese dissolved in the positive electrode active material with the external electrolyte, so it can also improve the cycle or storage stability of the battery. The measurement of the carbon coating layer in the present application and the measurement method of the thickness include any method in the art, such as high-power electron microscope, etc.

[0305] In these embodiments, the thickness of the carbon coating layer is any one of 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm or any one of the above-mentioned range values.

[0306] In some embodiments, the distance H between the first surface and the second surface is 0.1 mm to 0.2 mm.

[0307] In the above embodiments, the single-sided film layer thickness of the positive electrode tab is 0.1 mm to 0.2 mm.

[0308] [Positive electrode tab]

[0309] According to some embodiments of the present application, as described above, the positive electrode tab comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material.

[0310] The structure and composition of the positive electrode film layer of the present application are as described above, and will not be repeated here.

[0311] In some embodiments of the present application, the compaction density of the positive electrode film layer is 2.8 g / cm 3 ~ 3.4 g / cm 3 .

[0312] The compaction density of the positive electrode film layer of the present application can be used to characterize the energy density of the material. The compaction density of the positive electrode film layer = the area density of the positive electrode film layer / the thickness of the positive electrode film layer. The thickness of the positive electrode film layer includes the distance between the two end faces of the positive electrode film layer along the thickness direction. The area density of the positive electrode film layer = the weight of the single-sided positive electrode film layer / the area of the single-sided positive electrode film layer. The weight of the single-sided positive electrode film layer can be obtained by weighing, and the area of the single-sided positive electrode film layer can be obtained according to the area calculation formula according to the shape of the film layer.

[0313] In some embodiments of the present application, the positive electrode film layer contains the above-mentioned positive electrode active material, conductive agent, dispersing agent, and further contains a binder. The binder includes but is not limited to one or more than two combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0314] The forming method of the positive electrode film layer of the present application includes uniformly mixing the above-mentioned raw materials in a certain mass ratio with a solvent (such as nitrogen methyl pyrrolidone) to form a positive electrode slurry, uniformly coating the positive electrode slurry on both sides of the positive electrode current collector; controlling the single-sided coating weight to be 0.25 g ~ 0.50 g / 15 40.25 mm 2 ; after drying, compaction is carried out by a cold press to a certain compaction density (2.8 g / cm 3 ~ 3.4 g / cm 3 ), thereby obtaining a positive electrode sheet containing a positive electrode film layer.

[0315] [Negative electrode sheet]

[0316] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode film layer located on one side or both sides of the negative electrode current collector. Generally, the negative electrode film layer is located on both sides of the negative electrode current collector, and the forming method includes coating or deposition, etc. The present application will be described hereinafter taking both sides as an example.

[0317] In some embodiments of the present application, the compaction density of the negative electrode film layer is ≥ 1.65 g / cm 3 .

[0318] The compaction density of the negative electrode film layer in the present application can be used to represent the energy density of the material, but the compaction density of the negative electrode film layer is used to evaluate the compaction density of the whole negative electrode sheet. The compaction density of the negative electrode film layer = the area density of the negative electrode film layer / the thickness of the negative electrode film layer, the thickness of the negative electrode film layer includes the distance between the two end faces of the negative electrode film layer along the thickness direction, and the area density of the negative electrode film layer = the weight of the single-sided negative electrode film layer / the area of the single-sided negative electrode film layer, wherein the weight of the single-sided negative electrode film layer can be obtained by weighing, and the area of the single-sided negative electrode film layer can be obtained according to the area calculation formula according to the shape of the film layer. In the embodiments, the compaction density of the negative electrode film layer is ≥1.65 g / cm 3 .

[0319] In some embodiments, the negative electrode film layer disclosed in the present application comprises a negative electrode active material, and the negative electrode active material comprises one or more of carbonaceous material, silicon-based material, silicon-carbon composite material, tin-based and alloy material. The carbonaceous material in the present application comprises one or more of artificial graphite, natural graphite, soft carbon, hard carbon in combination. Among them, the artificial graphite, natural graphite, soft carbon, hard carbon and the like comprise any form of material in the prior art, and any manufacturer and model in the prior art. The silicon-based material in the present application comprises one or both of silicon-oxygen material or silicon-carbon material, or silicon-carbon composite. The tin-based and alloy material in the present application includes but is not limited to Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, etc. And the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of lithium ion batteries or sodium ion batteries can also be used. These negative electrode active materials can be used alone or in combination with two or more.

[0320] In some embodiments, the negative electrode film layer comprises a binder and a dispersing agent, etc., and the binder comprises but is not limited to polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, styrene-butadiene rubber (SBR), etc. The dispersing agent also comprises any kind in the prior art, such as cellulose and its salt, specifically comprising but not limited to methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0321] The forming method of the negative electrode film layer of the present application comprises mixing the above-mentioned raw materials in a certain mass ratio with a solvent (such as deionized water) to form a negative electrode slurry, degassing the negative electrode slurry, and then uniformly coating the negative electrode slurry on both sides of the negative electrode current collector; control the single-sided coating weight; dry, and compact to a certain compaction density by using a cold press, to obtain a negative electrode sheet comprising a negative electrode film layer.

[0322] [Separator]

[0323] The isolation member in some embodiments of the present application is not particularly limited in type, and any known porous structure isolation member with good chemical stability and mechanical stability can be selected.

[0324] In some embodiments, the isolation member includes a base material layer and a coating layer disposed on a surface of the base material layer; the base material of the base material layer includes one or more of polyethylene, polypropylene, poly-p-phenylene terephthalamide, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide; and the coating layer includes a ceramic coating layer and / or a polymer coating layer. The base material layer has good permeability to lithium ions, which is conducive to the migration of lithium ions; and the surface of the base material layer is provided with the coating layer, which can further improve the mechanical properties of the isolation film. Further, the ceramic particles in the ceramic coating layer include one or more of SiO2, Al2O3, AlOOH, CaO, TiO2, MgO, ZnO, ZrO2, Mg(OH)2, and BaSO4. Further, the polymer material of the polymer coating layer includes one or more of polyethylene (PE), polypropylene (PP), poly-p-phenylene terephthalamide (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and polyamide (PA). The polymer coating layer and the base material layer can be made of the same or different materials, and the thickness of the polymer coating layer and the base material layer can be different. Alternatively, the thickness of the polymer coating layer is less than that of the base material layer.

[0325] In some embodiments, the material of the isolation member can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation member can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the isolation member is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0326] [Electrolyte]

[0327] The electrolyte disclosed in some embodiments of the present application can be liquid, solid or gel. Among them, the solid is a solid electrolyte, the liquid is a liquid electrolyte, and the gel is a gel electrolyte. The secondary battery of the present application uses a liquid electrolyte, that is, an electrolyte. The electrolyte contains an electrolyte salt and an organic solvent. Among them, the type of electrolyte salt contains any type of conventional in the art, such as, including but not limited to inorganic metal salts, such as RClO4, RAsF6, RPF6, RBF4, RSbF6, RSO3F, RN(FSO2)2, etc.; fluorine-containing organic metal salts, such as RCF3SO3, RN(FSO2)(CF3SO2), RN(CF3SO2)2, RN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, RN(CF3SO2)(C4F9SO2), RC(CF3SO2)3, RPF4(CF3)2, RPF4(C2F5)2, RPF4(CF3SO2)2, RPF4(C2F5SO2)2, RBF2(CF3)2, RBF2(C2F5)2, RBF2(CF3SO2)2, RBF2(C2F5SO2)2, etc.; and dicarboxylic acid complex metal salt, such as lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, etc. The metal and R here both contain lithium ions.

[0328] According to some embodiments of the present application, the concentration of electrolyte salt in the electrolyte is 0.1 mol / L-4 mol / L. The present application discloses in these embodiments that the concentration of electrolyte salt is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4 mol / L or meets any of the above range values.

[0329] As described above, the organic solvent includes any one or more of a carboxylic acid ester compound, a carbonate compound, and an ether compound. Among them, the carboxylic acid ester compound includes one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL); the carbonate compound includes one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), and fluoroethylene carbonate (FEC). The ether compound includes at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvent of the present application further includes one or both of a nitrile solvent and a sulfone solvent. The nitrile solvent includes one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvent includes at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0330] According to some embodiments of the present application, the electrolyte further includes a film-forming stabilizer, which includes a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer includes a carbonate additive and / or a sulfate additive. The carbonate additive includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additive includes a cyclic sulfonate additive and / or a hydrocarbon sulfonate additive. Further, the cyclic sulfonate additive includes one or more of 1,3-propane sultone (PS), propene sultone (PES), and 3-fluoro-1,3-propane sultone (FPS). The hydrocarbon sulfonate additive includes one or more of vinyl sulfonate (DTD), diethyl sulfonate (DES), and dimethyl sulfonate (DMS). The negative electrode film-forming stabilizer includes one or more of a boron-lithium salt, a phosphorus-lithium salt, and a sulfur-lithium salt. The boron-lithium salt includes one or more of lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), and lithium bis(fluorooxalato)borate (LiDFOB). The phosphorus-lithium salt includes one or more of lithium difluorophosphate (LiPO2F2), lithium fluorophosphate (Li2PO3F), and lithium phosphate (Li3PO4). The sulfur-lithium salt includes one or more of lithium fluorosulfonate (LiFSO3), lithium sulfate (Li2SO4), and lithium sulfamate (LiSO3NH2).

[0331] The secondary battery of the present application will be described below with emphasis on specific examples.

[0332] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0333] The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0334] The present application can employ conventional techniques of inorganic chemistry within the skill of the art. In the following examples, efforts have been made to ensure accuracy with respect to numbers (quantities, temperatures, reaction times, etc.) but some experimental errors and deviations should be accounted for. Temperatures used in the following examples are expressed in °C, and pressures are at or near atmospheric pressure. All reagent chemicals were obtained in AR grade, and all reactions were carried out under an argon atmosphere. Unless otherwise indicated, all reagents were obtained from commercial sources.

[0335] Experimental materials:

[0336] 1. Lithium iron manganese phosphate, lithium iron phosphate, lithium manganese phosphate: commercially available;

[0337] 2. Carbon nanotubes: Wuxi Dongheng New Energy Technology Co., Ltd.;

[0338] 3. Dispersant - hydrogenated butyl rubber and its modified compounds: Zeon Corporation;

[0339] Dispersant - polyvinylidene fluoride and its modified compounds: China Blue Sky Group Co., Ltd.;

[0340] 4. Carbon black: Jiangxi Heicat Carbon Black Co., Ltd.;

[0341] 5. Graphene: commercially available;

[0342] The performance parameters of some of the experimental materials are as follows:

[0343] Table 1-1 Parameter List of Positive Electrode Active Material

[0344]

[0345] Table 1-2 Parameter List of Carbon Nanotubes

[0346]

[0347] Table 1-3 Parameter List of Carbon Black

[0348] Serial number Specific surface area BET / m 2 / g]]> 3-1 381

[0349] Table 1-4 Parameter List of Graphene

[0350] Serial number Number of layers Average particle diameter / pm 4-1 3 5.0

[0351] Table 1-5 Parameter list of hydrogenated nitrile rubber

[0352] Serial number Acrylonitrile content (%) Hydrogenation degree (%) Weight average molecular weight 5-1 34％ 99.5％ 212386

[0353] Table 1-6 Parameter list of polyvinylidene fluoride

[0354] Serial number Crystallinity Weight average molecular weight 6-1 50.2％ 2.26 million

[0355] Example 1 (double-layer multi-coating, different single-wall carbon nanotube contents)

[0356] A secondary battery is provided, which includes a positive electrode sheet, a separator, and a negative electrode sheet which are sequentially stacked, and further includes an electrolyte.

[0357] A positive electrode sheet is prepared, including the following steps:

[0358] (1) Preparation of carbon nanotube dispersion liquid: carbon nanotube powder 2-1 and hydrogenated nitrile rubber 5-1 are dispersed into N-methyl pyrrolidone to form a carbon nanotube dispersion liquid;

[0359] (2) Preparation of first positive electrode slurry: lithium manganese iron phosphate 1-3 (LiFe 0.1 Mn 0.9 O4), the above-mentioned carbon nanotube dispersion liquid, and adhesive styrene-butadiene rubber are mixed together, and after stirring with N-methyl pyrrolidone solvent, a first positive electrode slurry is formed;

[0360] (3) Preparation of second positive electrode slurry: lithium manganese iron phosphate 1-3 (LiFe 0.1 Mn 0.9 O4), the above-mentioned carbon nanotube dispersion liquid, and adhesive styrene-butadiene rubber are mixed together, and after stirring with N-methyl pyrrolidone solvent, a second positive electrode slurry is formed; the difference between the second positive electrode slurry and the first positive electrode slurry is that the amount of the carbon nanotube dispersion liquid added is different so that the carbon nanotube content in the first sub-positive electrode film layer and the second sub-positive electrode film layer is different;

[0361] (4) Preparation of positive electrode sheet: the first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain a first sub-positive electrode film layer, wherein in the first sub-positive electrode film layer, the mass percentage contents of LiFe 0.1 Mn 0.9 O4, carbon nanotube, and hydrogenated nitrile rubber are as shown in Table 2-1.

[0362] The second positive electrode slurry is coated on both surfaces of the first sub-positive electrode film layer to obtain a second sub-positive electrode film layer, wherein in the second sub-positive electrode film layer, the mass percentage contents of LiFe 0.1 Mn 0.9 O4, carbon nanotube, and hydrogenated nitrile rubber are as shown in Table 2-1.

[0363] The thickness H of the positive electrode film layer is 0.15 mm, wherein the thicknesses of the first and second sub-positive electrode film layers are 0.075 mm respectively.

[0364] The negative electrode sheet was prepared as follows:

[0365] The graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickening agent sodium carboxymethyl cellulose (CMC-Na) were dissolved in deionized water according to a weight ratio of 96.2:1.8:0.8:1.2, and stirred in a vacuum stirrer until the system was uniform. The negative electrode slurry was uniformly coated on both sides of the negative electrode current collector copper foil. A nine-section oven was used for drying, with the temperature settings being 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃ in sequence. Then, a cold press was used for compaction, and the negative electrode sheet was prepared.

[0366] The electrolyte was prepared as follows:

[0367] In an environment with a water content of less than 10 ppm, non-aqueous organic solvents ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed according to a volume ratio of 1:1:1 to obtain a solvent. Lithium salt lithium hexafluorophosphate was added to the solvent to form an electrolyte with a lithium hexafluorophosphate concentration of 1 mol / L.

[0368] The separator film was provided as follows:

[0369] A porous polyethylene (PE) film was used as the separator film, with a thickness of 13 μm.

[0370] The battery monomer was prepared as follows:

[0371] The above positive electrode sheet, separator film, and negative electrode sheet were stacked in sequence, with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role. A stack bare cell was formed by corresponding assembly. The stack bare cell was placed in an outer packaging shell, and after drying, the electrolyte was injected. After vacuum packaging, standing, formation, and shaping processes, the battery monomer was obtained.

[0372] Example 1-1 (double-layer single-coating, same carbon tube content)

[0373] A secondary battery was provided, which differed from Example 1 in that the first positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil to obtain a positive electrode film layer with a thickness of H.

[0374] The other parts of this embodiment 1-1 were the same as those of Example 1.

[0375] Comparative Example 1

[0376] A battery cell is provided, which is different from the above-mentioned embodiment 2-1 in that the positive electrode active material is replaced by lithium manganese phosphate (No. 1-2 in Table 1-1), and the conductive agent is replaced by carbon black (No. 3-1 in Table 1-3), and the mass ratio of lithium manganese phosphate, carbon black 3-1, hydrogenated butyl nitrile rubber 5-1 and adhesive styrene butadiene rubber is 94%:2.5%:1.5%:2%, and the others are the same as embodiment 2-1.

[0377] Embodiment 2-1 (double-layer multi-coating, different manganese content, different carbon tube content)

[0378] A secondary battery is provided, which is different from embodiment 1 in that the positive electrode sheet is different.

[0379] (1) Preparation of first carbon nanotube dispersion liquid: carbon nanotube powder 2-1 and hydrogenated butyl nitrile rubber 5-1 are dispersed into nitrogen methyl pyrrolidone to form a first carbon nanotube dispersion liquid;

[0380] (2) Preparation of second carbon nanotube dispersion liquid: carbon nanotube powder 2-2 and hydrogenated butyl nitrile rubber 5-1 are dispersed into nitrogen methyl pyrrolidone to form a second carbon nanotube dispersion liquid;

[0381] (3) Preparation of first positive electrode slurry: lithium manganese iron phosphate 1-3 (LiFe 0.1 Mn 0.9 O4), first carbon nanotube dispersion liquid and adhesive styrene butadiene rubber are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, a first positive electrode slurry is formed;

[0382] (4) Preparation of second positive electrode slurry: lithium manganese iron phosphate 1-6 (LiFe 0.8 Mn 0.2 O4), second carbon nanotube dispersion liquid and adhesive styrene butadiene rubber are mixed together, and after stirring with nitrogen methyl pyrrolidone solvent, a first positive electrode slurry is formed; the second positive electrode slurry is different from the first positive electrode slurry in that the type of positive electrode active material is different, and the content of carbon nanotubes is also different.

[0383] (5) Preparation of positive electrode sheet: the first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain a first sub-positive electrode film layer, wherein in the first sub-positive electrode film layer, the mass percentage content of LiFe 0.1 Mn 0.9 O4, carbon nanotube, hydrogenated butyl nitrile rubber is shown in Table 2-1.

[0384] The second positive electrode slurry is coated on both surfaces of the first sub-positive electrode film layer to obtain a second sub-positive electrode film layer, wherein in the second sub-positive electrode film layer, the mass percentage content of LiFe 0.8 Mn 0.2The mass percentage contents of O4, carbon nanotubes, and hydrogenated butadiene-acrylonitrile rubber are shown in Table 2-1. The other parts of this embodiment 2-1 are the same as those of embodiment 1.

[0385] Embodiment 2-2 (three-layer multi-coating, different manganese content, different carbon tube content)

[0386] A secondary battery is provided, which differs from embodiment 1 in that the positive electrode sheet is different.

[0387] (1) Preparation of the first carbon nanotube dispersion liquid: carbon nanotube powder 2-1 and hydrogenated butadiene-acrylonitrile rubber 5-1 are dispersed in nitrogen methyl pyrrolidone to form the first carbon nanotube dispersion liquid;

[0388] (2) Preparation of the third carbon nanotube dispersion liquid: carbon nanotube powder 2-3 and hydrogenated butadiene-acrylonitrile rubber 5-1 are dispersed in nitrogen methyl pyrrolidone to form the third carbon nanotube dispersion liquid;

[0389] (3) Preparation of the second carbon nanotube dispersion liquid: carbon nanotube powder 2-2 and hydrogenated butadiene-acrylonitrile rubber 5-1 are dispersed in nitrogen methyl pyrrolidone to form the second carbon nanotube dispersion liquid;

[0390] (4) Preparation of the first positive electrode slurry: lithium iron manganese phosphate 1-3 (LiFe 0.1 Mn 0.9 O4), the first carbon nanotube dispersion liquid, and the binder styrene-butadiene rubber are mixed together, and after stirring with the nitrogen methyl pyrrolidone solvent, a first positive electrode slurry with a solid content of 60% is formed;

[0391] (5) Preparation of the third positive electrode slurry: lithium iron manganese phosphate 1-7 (LiFe 0.6 Mn 0.4 O4), the third carbon nanotube dispersion liquid, and the binder styrene-butadiene rubber are mixed together, and after stirring with the nitrogen methyl pyrrolidone solvent, a third positive electrode slurry with a solid content of 60% is formed;

[0392] (4) Preparation of the second positive electrode slurry: lithium iron manganese phosphate 1-6 (LiFe 0.8 Mn 0.2 O4), the second carbon nanotube dispersion liquid, and the binder styrene-butadiene rubber are mixed together, and after stirring with the nitrogen methyl pyrrolidone solvent, a first positive electrode slurry with a solid content of 60% is formed; the second positive electrode slurry differs from the first positive electrode slurry and the third positive electrode slurry in that the types of positive electrode active materials are different, and the types and contents of carbon nanotubes are different.

[0393] (5) Preparation of the positive electrode sheet: the first positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil to obtain a first sub-positive electrode film layer, wherein in the first sub-positive electrode film layer, LiFe 0.1 Mn 0.9O4, carbon nanotube, hydrogenated nitrile rubber, and the mass percentage content of the adhesive is 96.5%, 1.0%, 1.5%, and 1.0%, respectively.

[0394] The third positive electrode slurry is coated on both surfaces of the first sub-positive electrode film layer to obtain a third sub-positive electrode film layer, wherein in the third sub-positive electrode film layer, the mass percentage content of LiFe 0.6 Mn 0.4 O4, carbon nanotube, hydrogenated nitrile rubber, and the mass percentage content of the adhesive is 96.5%, 1.0%, 1.5%, and 1.0%, respectively.

[0395] The second positive electrode slurry is coated on both surfaces of the third sub-positive electrode film layer to obtain a second sub-positive electrode film layer, wherein in the second sub-positive electrode film layer, the mass percentage content of LiFe 0.8 Mn 0.2 O4, carbon nanotube, hydrogenated nitrile rubber, and the mass percentage content of the adhesive is 96.5%, 1.0%, 1.5%, and 1.0%, respectively.

[0396] Example 3-1 (double-layer multi-coating, different carbon tube content, plus doping)

[0397] A secondary battery is provided, which is different from Example 2-1 in that the lithium manganese iron phosphate 1-3 (LiFe 0.1 Mn 0.9 O4) in the first positive electrode slurry is replaced by 1-5 (LiFe 0.05 Mn 0.9 Al 0.05 O4) in Table 1-1, and the other parts of this example remain the same as Example 2-1.

[0398] Example 4-1 (double-layer multi-coating, different carbon tube content, plus carbon coating)

[0399] A secondary battery is provided, which is different from Example 2-1 in that the lithium manganese iron phosphate 1-3 (LiFe 0.1 Mn 0.9 O4) in the first positive electrode slurry is replaced by 1-4 (carbon coating layer thickness is 0.053 μm) in Table 1-1, and the other parts of this example remain the same as Example 2-1.

[0400] Example 5-1 (double-layer multi-coating, each layer of conductive agent includes carbon tube + graphene + carbon black)

[0401] A secondary battery is provided, which is different from Example 2-1 in that the positive electrode sheet is different.

[0402] (1) Preparation of a first conductive agent dispersion liquid: carbon nanotube powder 2-1, carbon black 3-1, graphene 4-1, and hydrogenated butadiene rubber 5-1 were dispersed in nitrogen methyl pyrrolidone to form a first conductive agent dispersion liquid;

[0403] (2) Preparation of a second conductive agent dispersion liquid: carbon nanotube powder 2-2, carbon black 3-1, graphene 4-1, and hydrogenated butadiene rubber 5-1 were dispersed in nitrogen methyl pyrrolidone to form a second conductive agent dispersion liquid;

[0404] (3) Preparation of a first positive electrode slurry: lithium manganese iron phosphate 1-3 (LiFe 0.1 Mn 0.9 O4), the first conductive agent dispersion liquid, and the adhesive styrene butadiene rubber were mixed together, and after stirring with the nitrogen methyl pyrrolidone solvent, a first positive electrode slurry was formed;

[0405] (4) Preparation of a second positive electrode slurry: lithium manganese iron phosphate 1-6 (LiFe 0.8 Mn 0.2 O4), the second conductive agent dispersion liquid, and the adhesive styrene butadiene rubber were mixed together, and after stirring with the nitrogen methyl pyrrolidone solvent, a first positive electrode slurry was formed; the difference between the second positive electrode slurry and the first positive electrode slurry is that the types of positive electrode active materials are different, and the types and contents of the conductive agents are also different.

[0406] (5) Preparation of a positive electrode sheet: the first positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil to obtain a first sub-positive electrode film layer, wherein the mass percentage contents of LiFe 0.1 Mn 0.9 O4, carbon nanotubes, and hydrogenated butadiene rubber in the first sub-positive electrode film layer are shown in Table 2-1.

[0407] The second positive electrode slurry was coated on both surfaces of the first sub-positive electrode film layer to obtain a second sub-positive electrode film layer, wherein the mass percentage contents of LiFe 0.8 Mn 0.2 O4, carbon nanotubes, and hydrogenated butadiene rubber in the second sub-positive electrode film layer are shown in Table 2-3. The other parts of this embodiment 5-1 are the same as those of embodiment 2-1.

[0408] Example 6-1 (double-layer multi-coating, replacing dispersant)

[0409] A secondary battery is provided, which differs from example 2-1 in that the dispersant hydrogenated butadiene rubber 5-1 in the first carbon nanotube dispersion liquid and the second carbon nanotube dispersion liquid is replaced by polyvinylidene fluoride 6-1 of Table 1-6.

[0410] The other parts of this embodiment 6-1 are the same as those of example 2-1.

[0411] Example 7-1 (double layer coating, first layer of lithium manganese phosphate, second layer of lithium iron phosphate, same carbon tube content)

[0412] A secondary battery is provided, which differs from Example 2-1 in that:

[0413] The positive electrode active material in the first sub positive electrode film layer is lithium manganese phosphate 1-2 (LiMnO4) as shown in Table 1-1; the positive electrode active material in the second sub positive electrode film layer is lithium iron phosphate 1-1 (LiFeO4) as shown in Table 1-1, and the carbon nanotube content in the first sub positive electrode film layer and the second sub positive electrode film layer is the same.

[0414] The other parts of this Example 7-1 are the same as Example 2-1.

[0415] Example 7-2 (double layer coating, first layer of lithium manganese phosphate, second layer of lithium iron phosphate, different carbon tube content)

[0416] A secondary battery is provided, which differs from Example 8-1 in that: the carbon nanotube content in each sub positive electrode film layer in the positive electrode sheet is different. The other parts of this Example 7-2 are the same as Example 7-1.

[0417] The composition and proportion of the positive electrode film layers in the above-mentioned Examples 1, Example 1-1, Example 2-1, Example 3-1, Example 4-1, Example 6-1, Example 7-1, Example 7-2 of the present application are shown in Table 2-1 below.

[0418] Table 2-1 Composition of positive electrode film layer

[0419]

[0420]

[0421] The content of each component in each sub positive electrode film layer in Table 2-1 of the present application is 100%, and the remainder includes a binder and essential components.

[0422] The composition and proportion of the positive electrode film layers in the above-mentioned Example 2-2 are shown in Table 2-2 below.

[0423] Table 2-2 Composition of positive electrode film layer

[0424]

[0425] The content of each component in each sub positive electrode film layer in Table 2-2 of the present application is 100%, and the remainder includes a binder and essential components.

[0426] The composition and proportion of the positive electrode film layers in the above-mentioned Example 5-1 are shown in Table 2-3 below.

[0427] Table 2-3 Composition of positive electrode film layer

[0428]

[0429] In the above tables, the total mass percentage of each component in each sub-positive electrode film layer is 100%, and other components are binders or essential components except for the types and contents listed in the tables.

[0430] In the above tables, the test methods of the relevant parameters of each positive electrode tab in Table 2 are as follows:

[0431] ① Test method of film resistance:

[0432] The positive electrode tabs prepared in the above examples and comparative examples were cut into small round pieces of 10 mm in diameter at the left, middle and right positions of the dried tabs within a certain range. The power of the electrode resistance meter was turned on, and the electrode resistance meter was placed in the appropriate position of the "probe". The "start" button was clicked, and the reading was taken when the reading was stable. Two positions of each small round piece were tested, and the average value of six measurements was calculated as the film resistance of the tab. Table 2-4 was obtained.

[0433] Table 2-4 Film resistance of positive electrode tab

[0434]

[0435]

[0436] From the above Table 2-4, it can be seen that the use of positive active material and carbon nanotubes can significantly reduce the resistance of the positive electrode tab. In combination with Example 1 and Example 1-1, it can be seen that the more the amount of carbon nanotubes within a certain range, the more conducive to the conductivity. In combination with Example 1 and Example 2-1, it can be seen that within a certain range, the higher the content of iron in the positive active material lithium manganese iron phosphate, the less the demand for carbon nanotubes, but after the use of carbon nanotubes, it still shows good conductivity. In combination with Example 3-1 and 4-1, it can be seen that after the element doping and carbon coating of the positive active material, and the use of carbon nanotubes, good conductivity can also be achieved. This may be related to the fact that carbon nanotubes can be attached to the surface of the positive active material, shortening the electron conduction distance.

[0437] [Battery performance test]

[0438] ② Capacity retention rate after 1000 cycles:

[0439] The battery was charged at 1C constant current to 3.75V at 25°C, then charged at constant voltage to 0.05C (corresponding to 100% SOC), and then discharged at 1C constant current to the lower limit of 2.5V (corresponding to 0% SOC) after 5 min of standing, and the discharge capacity at this time was recorded as the discharge capacity of the first cycle. The battery was subjected to cycle charging and discharging tests according to the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the battery at 25°C after 1000 cycles = the discharge capacity after 1000 cycles / the discharge capacity of the first cycle x 100%.

[0440] ③Capacity retention rate of the battery (60°C) after 300 days of storage:

[0441] The battery was charged at 0.5C constant current to 3.75V at 25°C, then charged at constant voltage to 0.05C, and then discharged at 0.5C constant current to 2.5V after 5 min of standing. The discharge capacity at this time was the discharge capacity before storage. Then the battery was fully charged at a charging current of 0.5C and stored at 60°C for 300 days. After that, it was taken out and placed at 25°C for 2 hours, and then discharged at 0.5C constant current to 2.5V. After 5 min of standing, the battery was charged at 0.5C constant current to 3.75V, then charged at constant voltage to 0.05C, and then discharged at 0.5C constant current to 2.5V. The discharge capacity at this time was the discharge capacity after 300 days of storage.

[0442] Capacity retention rate of the battery after 300 days of storage at 60°C = (discharge capacity after 300 days of storage / discharge capacity before storage) x 100%.

[0443] According to the above test method, the test results shown in Table 3 are obtained.

[0444] Table 3 Performance list of the battery

[0445]

[0446]

[0447] From Tables 2-4 and Table 3, it can be seen that the design method of using different film layers in combination with different positive active materials and carbon nanotubes provided by the present application is beneficial to improving the conductivity of the electrode sheet to reduce the direct current resistance of the battery, and ultimately improving the performance of the battery. Further combining Example 2-1, Example 2-2 and Example 1 of Table 3, it can be seen that the design method of using different film layers in combination with different positive active materials and carbon nanotubes provided by the present application is beneficial to improving the cycle stability and storage stability of the battery to a certain extent, which may be due to reducing the manganese dissolution to a certain extent.

[0448] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be replaced equivalently. These modifications or replacements do not change the essence of the corresponding technical solutions, which should be covered in the scope of the present application. In particular, the technical features mentioned in each embodiment can be combined in any way as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery cell, characterized by: The positive electrode sheet and the negative electrode sheet are arranged in a stack; The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side surface of the positive electrode current collector; The positive electrode film layer has a first surface away from the positive electrode current collector and a second surface arranged opposite to the first surface; The distance between the first surface and the second surface is H; A region formed from the second surface of the positive electrode film layer to a position of 0.1×H in the stacking direction of the electrode sheet is referred to as a first region of the positive electrode film layer; A region formed from the first surface of the positive electrode film layer to a position of 0.1×H in the stacking direction of the electrode sheet is referred to as a second region of the positive electrode film layer; The first region comprises a first positive electrode active material and a first carbon nanotube, and the second region comprises a second positive electrode active material and a second carbon nanotube; The first positive electrode active material comprises any one or more of lithium manganese iron phosphate and lithium manganese phosphate; The second positive electrode active material comprises any one or more of lithium manganese iron phosphate and lithium iron phosphate; The mass percentage content of the first carbon nanotube in the first region is W1, and the mass percentage content of the second carbon nanotube in the second region is W2; W1≥W2.

2. The battery cell of claim 1, wherein: The mass percentage content of the first carbon nanotube in the first region is W1, and the mass percentage content of the second carbon nanotube in the second region is W2; W1≥W2. The first carbon nanotube or the second carbon nanotube each independently comprises any one or more of single-walled carbon nanotubes or multi-walled carbon nanotubes.

3. The battery cell of claim 1, wherein: The first carbon nanotube comprises single-walled carbon nanotubes, and the single-walled carbon nanotubes satisfy any one or more of the following properties:

4. The battery cell of claim 3, wherein: and / or; Average tube length greater than 50 pm; aspect ratio of 10-20; specific surface area of 800 m 2 / g ~ 1600 m 2 / g; The second carbon nanotube comprises multi-walled carbon nanotubes, and the multi-walled carbon nanotubes satisfy any one or more of the following properties: The first positive electrode active material comprises any one or more of lithium manganese iron phosphate and lithium manganese phosphate; The average tube length is 5-50 μm; the length-diameter ratio is 1.2-2.0; the specific surface area is 170-220 m 2 / g~220m 2 / g.

5. The battery cell of claim 1, wherein: The second positive electrode active material comprises lithium iron phosphate. The chemical formula of the lithium manganese iron phosphate is:

6. The battery cell of claim 1, wherein: wherein N represents a lithium-site doping element, the lithium-site doping element comprising any one or more of Zn, Al, Na, K, Mg, Nb, Mo, and W; Li a N b Fe x Mn y M 1-x-y P 1-m Q m O 4-n R n ; M represents a manganese-site and iron-site doping element, the manganese-site and iron-site doping element comprising any one or more of Al, Cu, Mg, Zn, Ni, Ti, V, Zr, Co, Ga, Sn, Sb, Nb; Q represents a phosphorus-site doping element, the phosphorus-site doping element comprising any one or more of B, S, Si, and N; R represents an oxygen-site doping element, the oxygen-site doping element comprising any one or more of S, F, Cl, and Br; a is 0.9 to 1.1; b is 0 to 0.1; x is 0.001 to 0.999; y is 0.001 to 0.999; 1-x-y is 0 to 0.1; m is 0 to 0.1; n is 0 to 0.

1. The manganese-site and iron-site doping element comprises any one or more of Al, Mg, and Ni; 7. The battery cell of claim 6, wherein: 1-x-y is 0.01 to 0.

1. ​ 8. The battery cell of claim 6 or 7, wherein: The first positive electrode active material comprises first lithium iron manganese phosphate, and the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1; The second positive electrode active material comprises second lithium iron manganese phosphate, and the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2; Y1≥Y2; Y1 or Y2 is independently selected from y x 100%.

9. The battery cell of claim 6, wherein: The positive electrode film layer comprises a first sub-positive electrode film layer and a second sub-positive electrode film layer which are stacked in sequence; The first sub-positive electrode film layer is located on at least one side surface of the positive electrode current collector; The second sub-positive electrode film layer is located on the side surface of the first sub-positive electrode film layer away from the positive electrode current collector; The first sub-positive electrode film layer comprises first lithium iron manganese phosphate and first carbon nanotubes, the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1, and 80% < Y1 < 100%; the mass percentage content of the first carbon nanotubes in the first sub-positive electrode film layer is W1, and 0.5% < W1 ≤ 1%; The second sub-positive electrode film layer comprises second lithium iron manganese phosphate and second carbon nanotubes, the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2, and 0 < Y2 ≤ 20%; the mass percentage content of the second carbon nanotubes in the second sub-positive electrode film layer is W2, and 0 < W2 ≤ 0.5%.

10. The battery cell of claim 6, wherein: The positive electrode film layer comprises a first sub-positive electrode film layer, a third sub-positive electrode film layer and a second sub-positive electrode film layer which are stacked in sequence; The first sub-positive electrode film layer is located on at least one side surface of the positive electrode current collector; The second sub-positive electrode film layer is located on the side surface of the first sub-positive electrode film layer away from the positive electrode current collector; The third sub-positive electrode film layer is located between the first sub-positive electrode film layer and the second sub-positive electrode film layer; The first sub-positive electrode film layer comprises first lithium iron manganese phosphate and first carbon nanotubes, the molar percentage content of manganese in the first lithium iron manganese phosphate is Y1, and 60% < Y1 < 100%; the mass percentage content of the first carbon nanotubes in the first sub-positive electrode film layer is W1, and 0.8% < W1 ≤ 1%; The third sub-positive electrode film layer comprises third lithium iron manganese phosphate and third carbon nanotubes, the molar percentage content of manganese in the third lithium iron manganese phosphate is Y3, and 20% < Y3 ≤ 60%; the mass percentage content of the third carbon nanotubes in the third sub-positive electrode film layer is W3, and 0.4 < W3 ≤ 0.8%; The second sub-positive electrode film layer comprises second lithium iron manganese phosphate and second carbon nanotubes, the molar percentage content of manganese in the second lithium iron manganese phosphate is Y2, and 0 < Y2 ≤ 20%; the mass percentage content of the second carbon nanotubes in the second sub-positive electrode film layer is W2, and 0 < W2 ≤ 0.4%.

11. The battery cell of claim 1, wherein: The positive electrode film layer further comprises any one or more of carbon black and graphene; The specific surface area of the carbon black is > 100 m 2 / g; And / or; The number of layers of the graphene is 1-10 layers, and the average flake diameter of each layer is 2 μm-8 μm; And / or; The mass percentage content of the carbon black and / or graphene in the positive electrode film layer is 0-2.5%.

12. The battery cell of claim 1, wherein: The positive electrode film layer further comprises a dispersant, the dispersant comprising any one or more of hydrogenated nitrile rubber and modified compounds thereof, and polyvinylidene fluoride and modified compounds thereof; The weight average molecular weight of the hydrogenated nitrile rubber and modified compounds thereof is 50,000-150,000; And / or; The hydrogenated nitrile rubber and modified compounds thereof comprise structural units derived from acrylonitrile monomers, the mass percentage content of the structural units derived from acrylonitrile monomers in the hydrogenated nitrile rubber and modified compounds thereof being 20%-40%; And / or; The hydrogenated nitrile rubber and modified compounds thereof have a hydrogenation degree of ≥99%; And / or; The weight average molecular weight of the polyvinylidene fluoride and modified compounds thereof is 2,000,000-4,000,000; And / or; The polyvinylidene fluoride and modified compounds thereof have a crystallinity of 40%-60%.

13. The battery cell of claim 1, wherein: The film sheet resistance of the positive electrode tab is ≤1Ω.

14. The battery cell of claim 1, wherein: The film sheet resistance of the positive electrode tab is 0.1Ω-1Ω.

15. The battery cell of claim 1, wherein: The particle size of the first positive electrode active material and / or the second positive electrode active material satisfies: Dv50 is 0.5μm-1.5μm; And / or; An outer side of the particles of the first positive electrode active material and / or the second positive electrode active material is formed with a carbon coating layer, the thickness of the carbon coating layer being 0.01μm-1μm.

16. The battery cell of claim 1, wherein: The distance H between the first surface and the second surface is 0.1mm-0.2mm.

17. A battery device, characterized by: The battery cell comprises any one of claims 1-16.

18. An electrical device, comprising: The battery device comprises claim 17.

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