Battery monomer, battery device, power utilization device and energy storage device

Abstract

The invention provides a battery monomer, a battery device, a power utilization device and an energy storage device. Each battery monomer comprises a positive pole piece, a negative pole piece and an electrolyte; the positive pole piece comprises a positive pole current collector and positive pole film layers arranged on at least one side of the positive pole current collector, and the positive pole film layers comprise a first positive pole film layer close to the positive pole current collector side and a second positive pole film layer arranged on the first positive pole film layer far away from the positive pole current collector side; the second positive electrode film layer comprises lithium-containing transition metal phosphate, the volume distribution particle size Dv99 of particles in the second positive electrode film layer is greater than or equal to 3.5 [mu] m, and the volume distribution particle size Dv99 of particles in the first positive electrode film layer is less than or equal to 3 [mu] m. The battery monomer provided by the invention has excellent energy density and safety performance.

Description

Technical Field

[0001] The present application relates to the technical field of battery cells, and in particular to a battery cell, a battery device, an electrical device and an energy storage device. Background Art

[0002] In recent years, battery monomers have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] As the market demands for the mileage and safety performance of electric devices increase, higher requirements are also put forward for the energy density, safety performance, cycle performance, etc. of battery cells. However, it is difficult to achieve the simultaneous improvement of the above performances in the existing technology, which has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] The present application is made in view of the above-mentioned problems, and its purpose is to provide a battery cell with good safety performance, high energy density and good cycle performance.

[0005] According to a first aspect of the present application, a battery cell is provided, wherein a positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one side of the positive electrode current collector, wherein the positive electrode film layer comprises a first positive electrode film layer close to the positive electrode current collector side and a second positive electrode film layer arranged on the first positive electrode film layer away from the positive electrode current collector side, wherein the second positive electrode film layer comprises a lithium-containing transition metal phosphate, wherein the volume distribution particle size Dv99 of the particles in the second positive electrode film layer is greater than or equal to 3.5 μm, and the volume distribution particle size Dv99 of the particles in the first positive electrode film layer is less than or equal to 3 μm.

[0006] The battery cell provided in the present application has a first positive electrode film layer added between the current collector and the second positive electrode film layer including a lithium transition metal phosphate. Among them, the Dv99 of the particles in the second positive electrode film layer is greater than or equal to 3.5μm, which helps to improve the energy density of the battery cell. However, the large particles in the second positive electrode film layer will lead to a decrease in the bonding force between the positive electrode film layer and the current collector, and the current collector leakage phenomenon is likely to occur when the pole piece is cut. By adding a first positive electrode film layer with particles having a Dv99 of less than or equal to 3μm between the current collector and the second positive electrode film layer, the particle size of the particles in the first positive electrode film layer is reduced, so that the number of particles in contact with the current collector is increased, and the binder content of the particles adhering to the current collector is increased, thereby improving the bonding force between the positive electrode film layer and the current collector, reducing the probability of current collector leakage, and improving the yield rate of pole piece cutting and the safety performance of the battery.

[0007] In any embodiment, the volume distribution particle size Dv99 of the particles in the second positive electrode film layer is 10-20 μm.

[0008] In any embodiment, the volume distribution particle size Dv99 of the particles in the first positive electrode film layer is 1-3 μm.

[0009] In any embodiment, the first positive electrode film layer further includes a binder, and based on the total mass of the first positive electrode film layer, the mass content of the binder is 0.5%-1.5%.

[0010] In any embodiment, the first positive electrode film layer also includes a binder. Based on the total mass of the first positive electrode film layer, the mass content of the binder can be selected to be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any numerical range therebetween.

[0011] The binder content in the first positive electrode film layer is within the above range, which is beneficial to increase the binder content of the first positive electrode film layer and the current collector, improve the bonding strength of the positive electrode film layer, and reduce the probability of leakage of the current collector during the cutting process of the electrode sheet.

[0012] In any embodiment, the first positive electrode film layer further includes a binder, and based on the total mass of the first positive electrode film layer, the mass content of the binder is 0.8%-1.3%.

[0013] Too high a binder content will cause the brittleness of the electrode to deteriorate severely and increase the resistance of the electrode. Studies have shown that when the binder content in the first positive electrode film layer is within the above range, it can improve the leakage of the electrode current collector while taking into account the brittleness of the electrode and the internal resistance of the battery, thereby improving the cycle performance and energy density of the battery.

[0014] In some embodiments, the binder includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid, polyimide (PI), and polyurethane (PU).

[0015] In some embodiments, the binder includes polyvinylidene fluoride.

[0016] The above-mentioned types of binders have good adhesion, which helps to improve the bonding strength between the positive electrode film layer and the current collector, improve the phenomenon of current collector leakage from the electrode, and thus improve the cycle performance of the battery.

[0017] In any embodiment, the number of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer accounts for greater than or equal to 50%.

[0018] In any embodiment, the number of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer accounts for greater than or equal to 75%.

[0019] The closer the roundness of the particles is to 1, the smoother the particles are. The increase in the roundness of the particles makes the arrangement of the particles in the first positive electrode film layer more uniform, and the surface flatness of the film layer is improved, thereby increasing the number of contact points between the particles close to the current collector and the current collector, increasing the bonding force between the positive electrode film layer and the current collector, and reducing the probability of the electrode sheet leaking the current collector during the cutting process, thereby improving the safety performance of the battery. At the same time, the increase in the roundness of the particles in the first positive electrode film layer reduces the tortuosity of the film layer, shortens the diffusion path of lithium ions, helps to reduce the increase of the DC impedance of the battery cell during the cycle, improves battery polarization, and improves the cycle performance and energy density of the battery.

[0020] In any embodiment, the number of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer accounts for greater than or equal to 98%.

[0021] The increase in the proportion of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer helps to further reduce the probability of collector leakage during the cutting process of the electrode, shorten the diffusion path of lithium ions, reduce the increase in DC impedance of the battery cell during the cycle, improve battery polarization, and further improve the battery's cycle performance and energy density.

[0022] In any embodiment, the first positive electrode film layer includes a lithium-containing transition metal phosphate, and the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer each independently includes a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I, Among them, 0.1≤x≤1.3, 0≤y≤1.3, and 0.8≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; and Y includes one or more of O and F.

[0023] In any embodiment, the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer independently includes one or more of lithium iron phosphate, lithium manganese phosphate, fluorolithium vanadium phosphate, lithium manganese iron phosphate, fluorolithium manganese iron phosphate and modified materials thereof.

[0024] The above-mentioned lithium-containing transition metal phosphate material has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0025] In any embodiment, the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer independently includes one or more of lithium iron phosphate and its modified materials.

[0026] In any embodiment, the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer includes lithium iron phosphate.

[0027] Both the first positive electrode film layer and the second positive electrode film layer contain lithium iron phosphate, and the voltage platform of the entire positive electrode system is consistent, which reduces the uneven current distribution and local overcharge / over-discharge problems caused by material differences, reduces the stress changes of the electrode during the cycle process, and thus improves the cycle stability of the battery.

[0028] In any embodiment, based on the total thickness of the positive electrode film layer, the first positive electrode film layer accounts for 0.2%-3%.

[0029] In any embodiment, based on the total thickness of the positive electrode film layer, the first positive electrode film layer accounts for 0.3%-1%.

[0030] Lithium-containing transition metal phosphates often have a low compaction density. In order to improve the energy density of the battery, the thickness of the positive electrode film layer needs to be increased. The embodiment of the present application can improve the leakage of the current collector through the first positive electrode film layer with a low thickness ratio, while taking into account the energy density of the battery.

[0031] In any embodiment, the single-side density of the first positive electrode film layer is 0.5-5 mg / 1540.25 mm 2 .

[0032] In any embodiment, the single-side density of the first positive electrode film layer is 1-2.5 mg / 1540.25 mm 2 .

[0033] The surface density of the first positive electrode film layer is within the above range, which can not only increase the bonding force between the positive electrode film layer and the current collector and reduce the probability of leakage of the current collector during the cutting process of the electrode sheet, but also reduce the loss of the positive electrode film layer compaction density caused by introducing the first positive electrode film layer between the second positive electrode film layer and the current collector, thereby taking into account the safety performance and energy density of the battery.

[0034] In any embodiment, the single-side density of the positive electrode film layer is 100-600 mg / 1540.25 mm 2 .

[0035] In any embodiment, the single-side density of the first positive electrode film layer is 250-500 mg / 1540.25 mm 2 .

[0036] The single-side density of the positive electrode film layer within the above range helps to improve the volume energy density of the battery.

[0037] In any embodiment, the volume distribution particle size Dv50 of the particles in the second positive electrode film layer is 0.5-1.5 μm.

[0038] In any embodiment, the volume distribution particle size Dv50 of the particles in the second positive electrode film layer is 0.5-1 μm.

[0039] The Dv50 of the particles in the second positive electrode film layer is within the range of 0.5-1.5μm, and further within the range of 0.5-1μm, which helps to reduce the stress concentration caused by the particles in the second positive electrode film layer, so that the low-thickness first positive electrode film layer can effectively reduce the probability of leakage of the collector. At the same time, the particle size is controlled within the above range, which helps to shorten the diffusion path of lithium ions, reduce the DCR of the battery cell, and take into account the gradation between particles, thereby improving the cycle performance and energy density of the battery.

[0040] In any embodiment, the particle size distribution of the particles in the second positive electrode film layer is (Dv90-Dv10) / Dv50 of 2-20.

[0041] In any embodiment, the particle size distribution of the particles in the second positive electrode film layer is (Dv90-Dv10) / Dv50 of 7-16.

[0042] The particle size distribution (Dv90-Dv10) / Dv50 indicates the concentration of particle size. The smaller the value, the more concentrated the particle size distribution, that is, the more uniform the particle size; conversely, the wider the particle size distribution, the greater the difference in particle size. The particle size distribution (Dv90-Dv10) / Dv50 of the particles in the second positive electrode film layer within the above range not only helps to improve the compaction density of the second negative electrode film layer according to the particle grading principle, but also helps to form a uniform pore structure between particles, improve the uniformity of lithium ion insertion and extraction, thereby taking into account both the energy density and cycle performance of the battery.

[0043] In any embodiment, the specific surface area of ​​the particles in the second positive electrode film layer is 5-15 cm 2 / g.

[0044] In any embodiment, the specific surface area of ​​the particles in the second positive electrode film layer is 8-13 cm 2 / g.

[0045] In any embodiment, the bonding strength between the positive electrode film layer and the positive electrode current collector is 56-141 N / m.

[0046] The bonding strength in the embodiment of the present application is within the above range, the positive electrode film layer has good adhesion to the current collector, which can effectively improve the current collector leakage phenomenon during the cutting process and improve the cycle performance of the battery.

[0047] In any embodiment, after the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets with leaking current collectors accounts for 0.1%-5.7%.

[0048] In any embodiment, after the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets with leaking current collectors accounts for 0.1%-0.8%.

[0049] In the embodiment of the present application, a first positive electrode film layer with particles having a Dv99 in the range of 0.1-3 μm is introduced between the second positive electrode film layer with particles having a Dv50 in the range of 0.5-1.5 μm and the current collector, which helps to reduce the probability of leakage of the current collector after the electrode sheet is cut and improve the safety performance of the battery.

[0050] In any embodiment, when the battery cell is fully discharged, the compaction density of the positive electrode film layer is 2.3-2.5 g / cm 3 .

[0051] When the battery cell is in a fully discharged state, the compaction density of the positive electrode film layer is within the above range, which is beneficial to improving the energy density of the battery cell.

[0052] A second aspect of the present application provides a battery device, which includes the battery cell provided by the first aspect.

[0053] A third aspect of the present application provides an electrical device, which includes the battery device provided in the second aspect, and the battery device is used to provide electrical energy.

[0054] A fourth aspect of the present application provides an energy storage device, which includes the battery device provided in the second aspect, and the battery device is used to store electrical energy.

[0055] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the multiple drawings represent the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings only depict some embodiments disclosed in the present application and should not be regarded as limiting the scope of the present application.

[0057] Figure 1This is a cross-sectional polished electron microscope morphology image of a positive electrode sheet in one embodiment of the present application; Figure 2 It is a graph showing the test data of the bonding strength of the pole piece according to an embodiment of the present application and a pair of ratios; Figure 3 is a schematic diagram of a battery cell provided in some embodiments of the present application; Figure 4 is a schematic diagram of a battery module provided in some embodiments of the present application; Figure 5 is a schematic diagram of a battery pack provided in some embodiments of the present application; Figure 6 yes Figure 5 An exploded schematic diagram of a battery pack is shown; Figure 7 is an exploded schematic diagram of a battery cell provided in some embodiments of the present application; Figure 8 It is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0058] Description of reference numerals: The reference numerals are as follows: 1. battery pack; 2. upper case; 3. lower case; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate; 6. positive electrode sheet; 61. positive electrode current collector; 62. positive electrode film layer; 621. first positive electrode film layer; 622. second positive electrode film layer. DETAILED DESCRIPTION

[0059] Hereinafter, the battery cells, battery devices and power devices of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0060] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0061] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0062] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0063] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0064] If there is no special explanation, the "include" and "comprising" mentioned in this application represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0065] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies 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).

[0066] In the present application, the terms "plurality" and "multiple" refer to two or more.

[0067] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0068] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be obtained by various test methods commonly used in the art. The measurement can be carried out, for example, according to the test method given in the examples of the present application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0069] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module or a battery pack.

[0070] A battery cell is the smallest unit of a battery, which can independently realize the functions of charging and discharging. The battery cell can be cylindrical, rectangular or in other shapes, etc., which is not limited in the embodiments of the present application. Figure 3 The battery cell 5 is a rectangular parallelepiped structure as an example.

[0071] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a box and battery cells, and the battery cells or battery modules are accommodated in the box. In some embodiments, the box may serve as part of the chassis structure of the vehicle. For example, part of the box may become at least a part of the floor of the vehicle, or part of the box may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0072] In some embodiments, the battery may be an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0073] In some embodiments, battery cells may be assembled into a battery module. The battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module. Figure 4FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 4 As shown, in the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0074] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0075] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0076] Figure 5 and Figure 6 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 5 and Figure 6 As shown, the battery pack 1 may include a box body and a plurality of battery modules 4 disposed in the box body. The box body includes an upper box body 2 and a lower box body 3, and the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the box body in any manner.

[0077] The battery provided in the embodiment of the present application may include a lithium-ion battery.

[0078] The battery cell includes an electrode assembly and an electrolyte. The electrode assembly can be a winding structure or a stacked structure, which is not limited in the present application.

[0079] The battery cell may also include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte. The outer package may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0080] In some embodiments, Figure 7 As shown, the outer package may include a shell 51 and a cover plate 53. The shell 51 may 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 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be adjusted according to demand.

[0081] The electrode assembly usually includes a positive electrode plate and a negative electrode plate. The negative electrode plate is the electrode that absorbs or lithiates lithium ions when the battery is charged and releases or delithiates lithium when the battery is discharged. The positive electrode plate is the electrode that releases or delithiates lithium ions when the battery is charged and absorbs or lithiates lithium when the battery is discharged.

[0082] As the market demands for the endurance of electrical devices increase, increasing the volume energy density of battery cells has become a common pursuit in the industry. The increase in the volume energy density of battery cells often requires an increase in the compaction density of the pole piece to increase the load of active materials per unit volume. However, researchers have found that after cutting, the pole piece with high compaction density leaks the current collector near its cut surface (the film layer near the cut surface falls off, resulting in the current collector being exposed), which affects the safety performance of the battery and cannot meet the use requirements of the battery cell.

[0083] In order to solve the above problems, the present application provides a battery cell in the first aspect, such as Figure 1 As shown, the positive electrode plate 6 includes a positive electrode collector 61 and a positive electrode film layer 62 arranged on at least one side of the positive electrode collector 61, the positive electrode film layer 62 includes a first positive electrode film layer 621 close to the positive electrode collector side and a second positive electrode film layer 622 arranged on the first positive electrode film layer 621 away from the positive electrode collector 61 side, the second positive electrode film layer 622 includes a lithium-containing transition metal phosphate, and the volume distribution particle size Dv99 of the particles in the second positive electrode film layer 622 is greater than or equal to 3.5μm; the volume distribution particle size Dv99 of the particles in the first positive electrode film layer 621 is less than or equal to 3μm.

[0084] Studies have shown that the generation of collector leakage during the slitting process of high compaction density pole pieces is closely related to the large particles in the pole piece film layer. In order to increase the compaction density of the pole piece, it is necessary to increase the proportion of large particles in the pole piece film layer to achieve a dense stacking of the film layer through the grading theory. However, large particles have a smaller specific surface area, less surface binder, and large particles will reduce the number of particles in contact with the current collector in the film layer, reduce the contact points with the current collector, and thus reduce the bonding force between the film layer and the current collector. During the slitting process, the film layer near the cut surface falls off under the action of shear force and current collector pressure, resulting in leakage of the current collector, affecting the safety performance of the battery.

[0085] Lithium-containing transition metal phosphates have good thermal stability, cycle stability and low cost, but their energy density needs to be improved, so it is necessary to increase the proportion of large particles in the material to increase the volume energy density of the battery. However, increasing the proportion of large particles will make the leakage of collectors more significant during the cutting process of the pole piece while improving the volume energy density.

[0086] The battery cell provided in the present application has a first positive electrode film layer added between the current collector and the second positive electrode film layer including a lithium transition metal phosphate. Among them, the Dv99 of the particles in the second positive electrode film layer is greater than or equal to 3.5μm, which helps to improve the energy density of the battery cell. However, the large particles in the second positive electrode film layer will lead to a decrease in the bonding strength between the positive electrode film layer and the current collector, which is prone to leakage of the current collector when the pole pieces are cut. By adding a first positive electrode film layer with particles having a Dv99 of less than or equal to 3μm between the current collector and the second positive electrode film layer, the particle size of the particles in the first positive electrode film layer is reduced, thereby increasing the number of particles in contact with the current collector, and increasing the content of the binder through which the particles adhere to the current collector, thereby improving the bonding strength between the positive electrode film layer and the current collector, such as Figure 2 As shown, the probability of collector leakage is reduced, and the yield rate of electrode cutting and the safety performance of the battery are improved.

[0087] In some embodiments, the volume distribution particle size Dv99 of the particles in the second positive electrode film layer is 10-20 μm.

[0088] In some embodiments, the volume distribution particle size Dv99 of the particles in the second positive electrode film layer can be selected as 3.5 μm, 4 μm, 4.2 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm , 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 16μm, 16.5μm, 16.7μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.2μm, 19.5μm, 20μm, 30μm, 50μm or any numerical range therebetween.

[0089] In some embodiments, the volume distribution particle size Dv99 of the particles in the first positive electrode film layer is 1-3 μm.

[0090] In some embodiments, the volume distribution particle size Dv99 of the particles in the first positive electrode film layer can be selected as 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.5μm, 2μm, 2.5μm, 2.8μm, 3μm or any numerical range therebetween.

[0091] When used in this article, the volume distribution particle sizes Dv50 and Dv99 have well-known meanings in the art, specifically the particle sizes corresponding to when the cumulative volume distribution percentage of the material reaches 50%, which can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer with reference to GB / T 19077-2016 particle size distribution laser diffraction method. The test instrument can be the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK. The examples are as follows: S1: Add 2g of positive electrode active material and 5g of sodium dodecyl sulfate SDS to 200mL of N-methylpyrrolidone (NMP), and then place it in an ultrasonic cleaner for ultrasonic treatment, set the power to 100W and the time to 30min, and take the solution after the ultrasonic treatment for particle size test; S2: Take 2g of positive electrode active material and 5g of sodium dodecyl sulfate SDS again and add them to 200mL of N-methylpyrrolidone (NMP), and then place it in an ultrasonic cleaner for ultrasonic treatment, set the power to 100W and the time to 30min, and take the solution after the ultrasonic treatment for particle size test; S2: Take 2g of positive electrode active material and 5g of sodium dodecyl sulfate SDS again and add them to 200mL of N-methylpyrrolidone (NMP), and then place it in an ultrasonic cleaner for ultrasonic treatment, set The power is set to 100W and the time is 60min. The solution after the ultrasonic treatment is taken for particle size test. If the Dv50 measured in steps S1 and S2 is greater than 5% or the fluctuation of Dv99 is greater than 5%, it is considered that the positive electrode active material is not completely dispersed. Repeat step S2 and increase the ultrasonic time by 30min until the fluctuations of Dv50 and Dv99 in two tests with a difference of 30min in ultrasonic time are both less than or equal to 5%. Stop the test, and the particle size distribution test result of the solution with the longest ultrasonic time is the particle size distribution of the positive electrode active material. Among them, the fluctuation of Dv50 is the ratio of the difference between the Dv50 of the two tests to the smaller Dv50 of the two test results; the fluctuation of Dv99 is the ratio of the difference between the Dv99 of the two tests to the smaller Dv99 of the two test results.

[0092] In some embodiments, the first positive electrode film layer further includes a binder, and based on the total mass of the first positive electrode film layer, the mass content of the binder is 0.5%-1.5%.

[0093] In some embodiments, the first positive electrode film layer also includes a binder. Based on the total mass of the first positive electrode film layer, the mass content of the binder can be selected to be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or any numerical range therebetween.

[0094] When used in this article, the content of the binder can be tested by methods and instruments known in the art, as shown below: place the positive electrode plate sample in an oven, set the oven temperature to 80°C and the time to 8h; then, use a scraper to scrape the dried positive electrode plate for powder treatment, and scrape 20mg of powder from the positive electrode film layer close to the positive electrode current collector side as the sample to be tested, place the sample to be tested in a hot gravity crucible, set the heating rate of the hot gravity crucible to 5°C / min, set the temperature to 25-800°C, heat it in a nitrogen atmosphere, record the weight loss curve of the sample in the entire temperature range, and calculate the weight loss rate of the test sample in the temperature range greater than or equal to 400°C, which is the mass proportion of the binder.

[0095] The binder content in the first positive electrode film layer is within the above range, which is beneficial to increase the binder content of the first positive electrode film layer and the current collector, improve the bonding strength of the positive electrode film layer, and reduce the probability of leakage of the current collector during the cutting process of the electrode sheet.

[0096] In some embodiments, the first positive electrode film layer further includes a binder, and based on the total mass of the first positive electrode film layer, the mass content of the binder is 0.8%-1.3%.

[0097] Too high a binder content will cause the brittleness of the electrode to deteriorate severely and increase the resistance of the electrode. Studies have shown that when the binder content in the first positive electrode film layer is within the above range, it can improve the leakage of the electrode current collector while taking into account the brittleness of the electrode and the internal resistance of the battery, thereby improving the cycle performance and energy density of the battery.

[0098] In some embodiments, the binder includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid, polyimide (PI), and polyurethane (PU).

[0099] In some embodiments, the binder includes polyvinylidene fluoride.

[0100] The above-mentioned types of binders have good adhesion, which helps to improve the bonding strength between the positive electrode film layer and the current collector, improve the phenomenon of current collector leakage from the electrode, and thus improve the cycle performance of the battery.

[0101] In some embodiments, the number of particles in the first positive electrode film layer having a roundness greater than or equal to 0.75 accounts for greater than or equal to 50%.

[0102] In some embodiments, the number of particles in the first positive electrode film layer having a roundness greater than or equal to 0.75 accounts for greater than or equal to 75%.

[0103] In some embodiments, the proportion of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer can be selected to be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100% or any numerical range therebetween.

[0104] As used herein, the definition of roundness is well known in the art, specifically the ratio of the shortest diameter R1 to the longest diameter R2 of a single particle, that is, roundness = R1 / R2. Roundness can be tested using methods or instruments known in the art, as shown below: the morphology of the material is photographed using a scanning electron microscope (SEM), and the roundness of the particles is automatically identified and counted using ImageJ software.

[0105] The test method for the proportion of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer is as follows: take a prepared positive electrode sheet, or a positive electrode sheet disassembled from a battery, and perform a CP-SEM test. It can be clearly observed in the obtained picture that there is a clear dividing line between the first positive electrode film layer and the second positive electrode film layer. The film layer particles close to the current collector side are smaller in size, and this layer is the first positive electrode film layer; the film layer particles away from the positive current collector side are larger, and this layer is the second positive electrode film layer. The ImageJ software is used to automatically identify and count the roundness of the particles in the first positive electrode film layer. The number of particles with a roundness greater than or equal to 0.75 is n1, and the total number of particles is n. The proportion of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer is equal to n1 / n.

[0106] The closer the roundness of the particles is to 1, the smoother the particles are. The increase in the roundness of the particles makes the arrangement of the particles in the first positive electrode film layer more uniform, and the surface flatness of the film layer is improved, thereby increasing the number of contact points between the particles close to the current collector and the current collector, increasing the bonding force between the positive electrode film layer and the current collector, and reducing the probability of the electrode sheet leaking the current collector during the cutting process, thereby improving the safety performance of the battery. At the same time, the increase in the roundness of the particles in the first positive electrode film layer reduces the tortuosity of the film layer, shortens the diffusion path of lithium ions, helps to reduce the increase of the DC impedance of the battery cell during the cycle, improves battery polarization, and improves the cycle performance and energy density of the battery.

[0107] In some embodiments, the number of particles in the first positive electrode film layer having a roundness greater than or equal to 0.75 accounts for greater than or equal to 98%.

[0108] The increase in the proportion of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer helps to further reduce the probability of collector leakage during the cutting process of the electrode, shorten the diffusion path of lithium ions, reduce the increase in DC impedance of the battery cell during the cycle, improve battery polarization, and further improve the battery's cycle performance and energy density.

[0109] In some embodiments, the first positive electrode film layer includes a lithium-containing transition metal phosphate, and the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer each independently includes a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I, Among them, 0.1≤x≤1.3, 0≤y≤1.3, and 0.8≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; and Y includes one or more of O and F.

[0110] In some embodiments, x can be selected to be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, or any range therebetween.

[0111] In some embodiments, y can be selected to be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, or any range therebetween.

[0112] In some embodiments, x+y may be selected to be 0.8, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, or any range therebetween.

[0113] In some embodiments, a may be selected to be 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, or any range therebetween.

[0114] In some embodiments, b may be selected to be 0, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any range therebetween.

[0115] In some embodiments, a+b may be selected to be 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.3, 1.4, 1.5, or any range therebetween.

[0116] In some embodiments, c may be selected to be 0, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or any range therebetween.

[0117] In some embodiments, z may be selected as 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, or any range therebetween.

[0118] In some embodiments, the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer independently includes one or more of lithium iron phosphate, lithium manganese phosphate, fluorolithium vanadium phosphate, lithium manganese iron phosphate, fluorolithium manganese iron phosphate and modified materials thereof.

[0119] The above-mentioned lithium-containing transition metal phosphate material has good thermal stability, cycle stability, etc., which helps to improve the safety performance and cycle performance of the battery.

[0120] In some embodiments, the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer independently includes one or more of lithium iron phosphate and its modified materials.

[0121] In some embodiments, the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer both include lithium iron phosphate.

[0122] Both the first positive electrode film layer and the second positive electrode film layer contain lithium iron phosphate, and the voltage platform of the entire positive electrode system is consistent, which reduces the uneven current distribution and local overcharge / over-discharge problems caused by material differences, reduces the stress changes of the electrode during the cycle process, and thus improves the cycle stability of the battery.

[0123] In some embodiments, based on the total thickness of the positive electrode film layer, the first positive electrode film layer accounts for 0.2%-3%.

[0124] In some embodiments, based on the total thickness of the positive electrode film layer, the first positive electrode film layer accounts for 0.3%-1%.

[0125] In some embodiments, based on the total thickness of the positive electrode film layer, the proportion of the first positive electrode film layer may be selected to be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3% or any numerical range therebetween.

[0126] Based on the total thickness of the positive electrode film layer, the proportion of the first positive electrode film layer can be tested by methods and equipment known in the art, as shown below: the first positive electrode film layer has a smaller particle size, so in the CP-SEM image of the cross section of the positive electrode sheet, the first positive electrode film layer and the second positive electrode film layer have a clear boundary, and the thickness A1 of the first positive electrode film layer in the image and the thickness A2 of the second positive electrode film layer in the image are vertically marked using the Adobe software of SEM. According to the measurement results and the ruler, the thickness L1 of the first positive electrode film layer and the thickness L2 of the second positive electrode film layer are converted, the thickness L of the positive electrode film layer = L1 + L2, and the proportion of the first positive electrode film layer is = L1 / L.

[0127] Lithium-containing transition metal phosphates often have a low compaction density. In order to improve the energy density of the battery, the thickness of the positive electrode film layer needs to be increased. The embodiment of the present application can improve the leakage of the current collector through the first positive electrode film layer with a low thickness ratio, while taking into account the energy density of the battery.

[0128] In some embodiments, the single-side density of the first positive electrode film layer is 0.5-5 mg / 1540.25 mm 2 .

[0129] In some embodiments, the single-side density of the first positive electrode film layer is 1-2.5 mg / 1540.25 mm 2 .

[0130] In some embodiments, the single-side density of the first positive electrode film layer can be selected to be 0.5 mg / 1540.25 mm 2 、1mg / 1540.25mm 2 , 1.5mg / 1540.25mm 2 , 2mg / 1540.25mm 2 , 2.5mg / 1540.25mm 2 、3mg / 1540.25mm 2 、3.5mg / 1540.25mm 2 ,4mg / 1540.25mm 2 4.5mg / 1540.25mm 2, 5mg / 1540.25mm 2 Or any range of values ​​in between.

[0131] The surface density of the first positive electrode film layer is within the above range, which can not only increase the bonding force between the positive electrode film layer and the current collector and reduce the probability of leakage of the current collector during the cutting process of the electrode sheet, but also reduce the loss of the positive electrode film layer compaction density caused by introducing the first positive electrode film layer between the second positive electrode film layer and the current collector, thereby taking into account the safety performance and energy density of the battery.

[0132] In some embodiments, the single-side density of the positive electrode film layer is 100-600 mg / 1540.25 mm 2 .

[0133] In some embodiments, the single-side density of the first positive electrode film layer is 250-500 mg / 1540.25 mm 2 .

[0134] In some embodiments, the single-side density of the positive electrode film layer can be selected to be 100 mg / 1540.25 mm 2 、150mg / 1540.25mm 2 、200mg / 1540.25mm 2 , 250mg / 1540.25mm 2 、300mg / 1540.25mm 2 、350mg / 1540.25mm 2 , 400mg / 1540.25mm 2 、450mg / 1540.25mm 2 、500mg / 1540.25mm 2 、550mg / 1540.25mm 2 、600 mg / 1540.25 mm 2 Or any range of values ​​in between.

[0135] The single-side density of the positive electrode film layer is well known in the art and can be tested using methods and instruments known in the art. An example is as follows: take a single-sided coated and cold-pressed positive electrode sheet (if it is a double-sided coated positive electrode sheet, the positive electrode film layer on one side can be wiped off first), punch it into small discs with an area of ​​S1, weigh it, and record it as M1. Then wipe off the positive electrode film layer of the weighed positive electrode sheet, weigh the weight of the current collector, and record it as M0. The single-side density of the positive electrode film layer = (M1-M0) / S1. In order to ensure the accuracy of the test results, multiple groups (for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.

[0136] The single-side density of the positive electrode film layer within the above range helps to improve the volume energy density of the battery.

[0137] In some embodiments, the volume distribution particle size Dv50 of the particles in the second positive electrode film layer is 0.5-1.5 μm.

[0138] In some embodiments, the volume distribution particle size Dv50 of the particles in the second positive electrode film layer can be selected as 0.5 μm, 0.6 μm, 0.5 μm, 0.7 μm, 0.8 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm or any numerical range therebetween.

[0139] In some embodiments, the volume distribution particle size Dv50 of the particles in the second positive electrode film layer is 0.5-1 μm.

[0140] The Dv50 of the particles in the second positive electrode film layer is within the range of 0.5-1.5μm, and further within the range of 0.5-1μm, which helps to reduce the stress concentration caused by the particles in the second positive electrode film layer, so that the low-thickness first positive electrode film layer can effectively reduce the probability of leakage of the collector. At the same time, the particle size is controlled within the above range, which helps to shorten the diffusion path of lithium ions, reduce the DCR of the battery cell, and take into account the gradation between particles, thereby improving the cycle performance and energy density of the battery.

[0141] In some embodiments, the particle size distribution of the particles in the second positive electrode film layer is (Dv90-Dv10) / Dv50 of 2-20.

[0142] In some embodiments, the particle size distribution of the particles in the second positive electrode film layer is (Dv90-Dv10) / Dv50 of 7-16.

[0143] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the particles in the second positive electrode film layer can be selected as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or any range therebetween.

[0144] The particle size distribution (Dv90-Dv10) / Dv50 indicates the concentration of particle size. The smaller the value, the more concentrated the particle size distribution, that is, the more uniform the particle size; conversely, the wider the particle size distribution, the greater the difference in particle size. The particle size distribution (Dv90-Dv10) / Dv50 of the particles in the second positive electrode film layer within the above range not only helps to improve the compaction density of the second negative electrode film layer according to the particle grading principle, but also helps to form a uniform pore structure between particles, improve the uniformity of lithium ion insertion and extraction, thereby taking into account both the energy density and cycle performance of the battery.

[0145] In some embodiments, the specific surface area of ​​the particles in the second positive electrode film layer is 5-15 cm 2 / g.

[0146] In some embodiments, the specific surface area of ​​the particles in the second positive electrode film layer is 8-13 cm 2 / g.

[0147] In some embodiments, the specific surface area of ​​the particles in the second positive electrode film layer can be 5 cm 2 / g, 6cm 2 / g, 7cm 2 / g, 8cm 2 / g, 9cm 2 / g, 10cm 2 / g, 11cm 2 / g, 12cm 2 / g, 13cm 2 / g, 14cm 2 / g, 15cm 2 / g or any range of values ​​between them.

[0148] When used in this article, specific surface area is a well-known meaning in the art, specifically the total area per unit mass of material. It can be tested using methods and instruments known in the art. For example, reference can be made to GB / T19587-2017, using nitrogen adsorption specific surface area analysis test method test, and calculated using the BET (BrunauerEmmettTeller) method. The nitrogen adsorption specific surface area analysis test can be performed by the Tri-Star3020 specific surface area pore size analysis tester of Micromeritics, USA.

[0149] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector is 56-141 N / m.

[0150] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector may be selected to be 56 N / m, 60 N / m, 65 N / m, 70 N / m, 75 N / m, 80 N / m, 85 N / m, 90 N / m, 95 N / m, 100 N / m, 105 N / m, 110 N / m, 115 N / m, 120 N / m, 125 N / m, 130 N / m, 135 N / m, 140 N / m, 141 N / m or any range of values ​​therebetween.

[0151] As used herein, the term "bonding strength" has a well-known meaning in the art and can be tested using methods and instruments known in the art, with examples as follows: prepare a positive electrode sheet or disassemble a battery to obtain a positive electrode sheet, and cut the positive electrode sheet into a rectangular sample to be tested with a long side width of a and a short side width of b; use double-sided tape to stick the sample to be tested to the surface of a steel plate, and compact it with a roller to make it completely fit the sheet; bend one end of the positive current collector 180° in the opposite direction, that is, bend the long side of the positive current collector; fix the steel plate with the lower fixture of the high-speed rail tensile machine, and fix the bent end (short side) of the positive current collector with the upper fixture, adjust the angle of the current collector so that the upper and lower ends are in a vertical position, and stretch the sample at a speed of 50 mm / min until the current collector is completely peeled off from the surface of the sheet, record the displacement and force during the process, and the force when the forces are balanced is the bonding force F of the sheet, and the bonding strength is = bonding force F / b, in units of N / m.

[0152] The bonding strength in the embodiment of the present application is within the above range, the positive electrode film layer has good adhesion to the current collector, which can effectively improve the current collector leakage phenomenon during the cutting process and improve the cycle performance of the battery.

[0153] In some embodiments, after the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets with leaking current collectors accounts for 0.1%-5.7%.

[0154] In some embodiments, after the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets that leak current collectors accounts for 0.1%-0.8%.

[0155] In some embodiments, after the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets with leakage collector can be selected to be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.12%, 0.14%, 0.15%, 0.17%, 0.2%, 0.25%, 0.3%, 0.35%, 0.36%, 0.39%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 5.7% or any numerical range therebetween.

[0156] As used herein, the term "current collector leakage" refers to the phenomenon that the film layer does not completely cover a certain surface of the current collector, so that the current collector is exposed. The number and proportion of positive electrode sheets that leak the current collector after the positive electrode sheet is cut at a cutting speed of 0.5m / s can be tested using methods and instruments known in the art, as shown below: After the positive electrode sheet is cut at a cutting speed of 0.5m / s, a high-resolution electron microscope (CCD) is used to take micrographs of 1000 positive electrode film layers away from the side of the current collector. If a bright spot or bright edge appears at the cutting point of the sheet in the micrograph, it is identified as a positive electrode sheet that leaks the current collector. The number of leaking current collector sheets is counted as n2, and the number of positive electrode sheets that leak the current collector accounts for (n2 / 1000)×100%.

[0157] In the embodiment of the present application, a first positive electrode film layer with particles having a Dv99 in the range of 0.1-3 μm is introduced between the second positive electrode film layer with particles having a Dv50 in the range of 0.5-1.5 μm and the current collector, which helps to reduce the probability of leakage of the current collector after the electrode sheet is cut and improve the safety performance of the battery.

[0158] In some embodiments, when the battery cell is fully discharged, the compaction density of the positive electrode film layer is 2.3-2.5 g / cm 3 .

[0159] In some embodiments, when the battery cell is fully discharged, the compaction density of the positive electrode film layer can be selected to be 2.55 g / cm 3 , 2.3g / cm 3 , 2.31g / cm 3 , 2.32g / cm 3 , 2.33g / cm 3 , 2.34g / cm 3 , 2.35g / cm 3 , 2.36g / cm 3 , 2.37g / cm 3 , 2.38g / cm 3 , 2.39g / cm 3 , 2.4g / cm 3 , 2.41g / cm 3 , 2.42g / cm 3 , 2.43g / cm 3 , 2.44g / cm 3 , 2.45g / cm 3 , 2.46g / cm 3 , 2.47g / cm 3 , 2.48g / cm 3 , 2.49g / cm 3 , 2.5g / cm 3 Or any range of values ​​in between.

[0160] The compaction density of the positive electrode film layer can be tested by methods known in the art. As an example, disassemble the battery cell in a fully charged state, take out the positive electrode plate, wash the positive electrode plate with a solvent for more than three times and dry it, and then use an electronic balance to weigh the positive electrode plate test sample with an area of ​​S. The weight is recorded as W1, and the thickness of the positive electrode plate T1 is measured using a micrometer. Then wipe off the weighed electrode film layer, weigh the weight of the positive electrode collector, record it as W2, and use a micrometer to measure the thickness of the positive electrode collector T2. Then the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0161] When the battery cell is in a fully discharged state, the compaction density of the positive electrode film layer is within the above range, which is beneficial to improving the energy density of the battery cell.

[0162] Battery device The embodiment of the present application also provides a battery device, the battery device includes the battery cell provided in the embodiment of the present application, and the battery device is used to provide a device. The battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

[0163] Electrical devices The embodiment of the present application also provides an electric device, which includes a battery device provided in the embodiment of the present application, and the battery device is used to provide electrical energy. The battery can be used as a power source for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop 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, etc.

[0164] The electrical device can select a specific type of battery, such as a battery cell, a battery module or a battery pack, according to its usage requirements.

[0165] Energy storage device The embodiment of the present application also provides an energy storage device, which includes a battery device provided in the embodiment of the present application, and the battery device is used to store electrical energy. The battery device can be used as an energy storage unit of the energy storage device. The energy storage unit can be, but is not limited to, an energy storage container, an energy storage cabinet, an energy storage power station, an energy storage battery pack, or a portable energy storage system.

[0166] Figure 8 Schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

[0167] As another example, the electric device may be a mobile phone, a tablet computer, a notebook computer, etc. The electric device is usually required to be light and thin, and a battery cell may be used as a power source.

[0168] Example Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0169] 3. Preparation method Example 1 (1) Preparation of positive electrode Preparation of the first cathode film slurry: LiFePO 4 , conductive carbon, and binder PVDF are dissolved in NMP (N-methylpyrrolidone) solvent in a mass ratio of 98:0.7:1.3, fully stirred and mixed, and then wetting, kneading and dispersing treatments are performed to obtain the first film layer positive electrode slurry.

[0170] Among them, based on the addition of LiFePO 4 Of the total mass, the mass of particles with a roundness greater than or equal to 0.75 accounts for 100%.

[0171] Preparation of the second cathode film slurry: LiFePO 4 , conductive carbon, and binder PVDF are dissolved in NMP (N-methylpyrrolidone) solvent in a weight ratio of 98:1:1, fully stirred and mixed, and then wetted, kneaded and dispersed to obtain the second film layer positive electrode slurry.

[0172] The first positive electrode slurry is coated on the aluminum foil to form a first positive electrode slurry coating, and the second positive electrode slurry is coated on the surface of the first positive electrode slurry to form a second positive electrode slurry coating; then dried, cold pressed, and cut on a slitting machine at a cutting speed of 0.5m / s to obtain positive electrode sheets.

[0173] The single-side density of the first positive electrode film layer is 2 mg / 1540.25 mm 2 ; The single-side density of the positive electrode film is 302mg / 1540.25mm 2 Based on the total mass of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 0.66%; the thickness of the second positive electrode film layer is LiFePO 4 The (Dv90-Dv10) / Dv50 of the particles is 12, and the specific surface area is 11cm 2 / g; the bonding strength between the positive electrode film layer and the positive electrode current collector is 123.5N / m; when the battery cell is fully discharged, the compaction density of the positive electrode film layer is 2.45g / cm 3 .

[0174] (2) Preparation of negative electrode sheet The negative electrode active material graphite, the binder polyvinyl alcohol, and the conductive agent SP-Li are mixed in a mass ratio of 90:5:5, and the solvent deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the surface of the negative electrode collector copper foil, and the negative electrode collector coated with the slurry is dried in a vacuum environment at 110°C, and then cold pressed and cut to obtain the negative electrode sheet.

[0175] (3) Preparation of electrolyte In an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm), organic solvents ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) were mixed evenly in a volume ratio of 1:1:1, and a certain amount of LiPF 6 The lithium salt is dissolved in an organic solvent, the concentration of the lithium salt is controlled to be 1 mol / L, and the mixture is stirred evenly to obtain an electrolyte.

[0176] (4) Isolation film Polyethylene film with a thickness of 13 μm.

[0177] (5) Preparation of batteries The positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrode sheets to play an isolating role, and then wound to obtain an electrode assembly. The electrode assembly is placed in a battery housing, and after drying, the electrolyte is injected, and then a lithium-ion battery is obtained through processes such as formation and static.

[0178] Example 2-3 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiFePO 4 The Dv99 of the particles is different, see Table 1 for details.

[0179] Example 4 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the mass proportion of PVDF in the first positive electrode slurry is different. Specifically, LiFePO 4 The mass ratio of conductive carbon and binder PVDF is 98.7:0.7:0.6, see Table 1 for details.

[0180] Example 5 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the mass proportion of PVDF in the first positive electrode slurry is different. Specifically, LiFePO 4 The mass ratio of conductive carbon and binder PVDF is 98.5:0.7:0.8, see Table 1 for details.

[0181] Example 6 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the mass proportion of PVDF in the first positive electrode slurry is different. Specifically, LiFePO 4 The mass ratio of conductive carbon and binder PVDF is 98.3:0.7:1, see Table 1 for details.

[0182] Example 7 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the mass proportion of PVDF in the first positive electrode slurry is different. Specifically, LiFePO 4 The mass ratio of conductive carbon and binder PVDF is 97.8:0.7:1.5, see Table 1 for details.

[0183] Example 8 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiFePO4 in the first positive electrode slurry has a roundness greater than or equal to 0.75. 4 The mass proportion of particles is 81%.

[0184] Example 9 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiFePO4 in the first positive electrode slurry has a roundness greater than or equal to 0.75. 4 The mass proportion of particles is 57%.

[0185] Embodiment 10-11 The preparation method of the lithium-ion battery is similar to that of Example 1, except that in the second positive electrode slurry, LiFePO 4 The Dv50 and Dv99 of the particles are different, see Table 1 for details.

[0186] Example 12 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiFePO 4 Replaced with LiFe 0.7 Mn 0.3 PO 4 , see Table 1 for details.

[0187] Comparative Example 1 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the positive electrode film layer does not have the first positive electrode film layer, but only includes the second positive electrode film layer, as shown in Table 1 for details.

[0188] Comparative Example 2 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiFePO 4 The Dv99 of different samples is different, see Table 1 for details.

[0189] Comparative Example 3 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the positive electrode film layer does not have the first positive electrode film layer, only includes the second positive electrode film layer, and the second positive electrode slurry contains LiFePO 4 The Dv50 and Dv99 are different, see Table 1 for details.

[0190] 2. Performance Test 1. Pole brittleness test Cut the electrode into 10cm×2cm strips of the sample to be tested. Fold the middle of the sample to be tested 180°, and apply 10N of pressure at the fold to make the fold fit together, then unfold the electrode to observe whether there is light transmission or powder loss at the fold. If there is no light transmission or powder loss, continue to repeat the above steps in the opposite direction, and each fold is counted as 0.5 times until light transmission or powder loss occurs at the fold of the electrode. Test at least ten samples, and take the average value of the cumulative folding times of all samples as the bending resistance of the positive electrode, that is, the brittleness level of the electrode.

[0191] 2. Battery volume energy density test The lithium-ion secondary battery was allowed to stand at 25°C for 2 hours. After charging the lithium-ion secondary battery at 0.33C to a charge cut-off voltage of 3.75V at 25°C, constant voltage charging was continued at the charge cut-off voltage until the current reached 0.05C and the charge was cut off (where C represents the rated capacity of the lithium-ion secondary battery). After the lithium-ion secondary battery was allowed to stand at 25°C for 1 hour, it was discharged at 0.33C at 25°C to a discharge cut-off voltage of 2.58V. The total discharge energy of the lithium-ion secondary battery was recorded as E0. Measure the length, width and height of the lithium-ion secondary battery, and calculate the volume value of the lithium-ion secondary battery V0 = length × width × height. The volume energy density of the lithium-ion secondary battery = lithium-ion secondary battery discharge energy E0 / lithium-ion secondary battery volume V0.

[0192] 3. Battery cycle retention rate test The lithium-ion secondary battery was left at 25°C for 2h, and then charged to 3.75V at 0.33C charging rate of the nominal capacity of the battery at 25°C, and then charged to 0.05C at 2.5V constant voltage, left at 10min, and then discharged to 2.58V at 0.33C discharge rate, and the reversible capacity was measured as C0. The above charge and discharge is a cycle, and after repeated charging and discharging for 1000 times, the battery capacity C1 is recorded, and the capacity retention rate at this cycle number is (C1 / C0)×100%.

[0193] 3. Test Results The test results of the above embodiments and comparative examples are shown in Tables 1 to 4.

[0194] Table 1

[0195] From the comparison between the embodiment and the comparative example, it can be seen that the second positive electrode film layer includes a lithium-containing transition metal phosphate, the volume distribution particle size Dv99 of the particles in the second positive electrode film layer is greater than or equal to 3.5 μm, and the volume distribution particle size Dv99 of the particles in the first positive electrode film layer is less than or equal to 3 μm, which helps to reduce the probability of collector leakage after the pole piece is cut, while taking into account the volume energy density of the battery.

[0196] Table 2

[0197] From the comparison between Example 1, Examples 5-6 and Examples 4 and Example 7, it can be seen that the binder content is in the range of 0.8%-1.3%, which is beneficial to further reduce the probability of collector leakage after the electrode sheet is cut, while taking into account the cell DCR and the electrode sheet brittleness, thereby helping to further improve the volume energy density and cycle performance of the battery.

[0198] Table 3

[0199] From the comparison between Example 1 and Examples 8-9, it can be seen that the number of particles with a roundness greater than or equal to 0.75 in the first positive electrode film layer accounts for greater than or equal to 75%, and further greater than or equal to 98%, which is beneficial to reducing the DCR of the battery cell and further improving the cycle performance and volume energy density of the battery.

[0200] Table 4

[0201] From the comparison between Example 1 and Example 12, it can be seen that the lithium transition metal phosphate containing in the first positive electrode film layer is made of lithium iron phosphate material, which helps to further improve the cycle performance of the battery.

[0202] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A battery cell, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode film layer includes a first positive electrode film layer close to the positive electrode current collector and a second positive electrode film layer disposed on the first positive electrode film layer away from the positive electrode current collector, wherein the second positive electrode film layer includes a lithium-containing transition metal phosphate. The volume distribution particle size Dv99 of the particles in the second positive electrode film layer is greater than or equal to 3.5 μm; The volume distribution particle size Dv99 of the particles in the first positive electrode film layer is less than or equal to 3 μm.

2. The battery cell according to claim 1, characterized in that: The volume distribution particle size Dv99 of the particles in the second positive electrode film layer is 10-20 μm.

3. The battery cell according to claim 1, characterized in that: The volume distribution particle size Dv99 of the particles in the first positive electrode film layer is 1-3 μm.

4. The battery cell according to claim 1, characterized in that: The first positive electrode film layer also includes a binder. Based on the total mass of the first positive electrode film layer, the mass content of the binder is 0.5%-1.5%.

5. The battery cell according to claim 4, characterized in that: The mass content of the binder is 0.8%-1.3%.

6. The battery cell according to claim 4, characterized in that: The binder includes one or more of polyvinylidene fluoride (PVDF), polyacrylic acid, polyimide (PI), and polyurethane (PU).

7. The battery cell according to claim 1, characterized in that: The number of particles in the first positive electrode film layer having a roundness greater than or equal to 0.75 accounts for greater than or equal to 50%.

8. The battery cell according to claim 1, characterized in that: The number of particles in the first positive electrode film layer having a roundness greater than or equal to 0.75 accounts for greater than or equal to 75%.

9. The battery cell according to claim 1, characterized in that: The number of particles in the first positive electrode film layer having a roundness greater than or equal to 0.75 accounts for greater than or equal to 98%.

10. The battery cell according to claim 1, characterized in that: The first positive electrode film layer includes a lithium-containing transition metal phosphate, and the lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer each independently includes a component represented by the following general formula: Li x A y Me a M b P 1-c X c Y z Formula I Among them, 0.1≤x≤1.3, 0≤y≤1.3, and 0.8≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A includes one or more of Na, K, and Mg; Me includes one or more of Mn, Fe, Co, and Ni; M includes one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X includes one or more of S, Si, Cl, B, C, and N; and Y includes one or more of O and F.

11. The battery cell according to claim 10, characterized in that: The lithium-containing transition metal phosphates in the first positive electrode film layer and the second positive electrode film layer independently include one or more of lithium iron phosphate, lithium manganese phosphate, fluorolithium vanadium phosphate, lithium manganese iron phosphate, fluorolithium manganese iron phosphate and modified materials thereof.

12. The battery cell according to claim 10, characterized in that: The lithium-containing transition metal phosphate in the first positive electrode film layer and the second positive electrode film layer independently includes one or more of lithium iron phosphate and its modified materials.

13. The battery cell according to claim 1, characterized in that: Based on the total thickness of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 0.2%-3%.

14. The battery cell according to claim 1, characterized in that: Based on the total thickness of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 0.3%-1%.

15. The battery cell according to claim 1, characterized in that: The single side density of the first positive electrode film layer is 0.5-5 mg / 1540.25 mm 2 .

16. The battery cell according to claim 1, characterized in that: The single-side density of the first positive electrode film layer is 1-2.5 mg / 1540.25 mm 2 .

17. The battery cell according to claim 1, characterized in that: The single-side density of the positive electrode film layer is 100-600 mg / 1540.25 mm 2 .

18. The battery cell according to claim 1, characterized in that: The single-side density of the positive electrode film layer is 250-500 mg / 1540.25 mm 2 .

19. The battery cell according to claim 1, characterized in that: The volume distribution particle size Dv50 of the particles in the second positive electrode film layer is 0.5-1.5 μm.

20. The battery cell according to claim 1, characterized in that: The volume distribution particle size Dv50 of the particles in the second positive electrode film layer is 0.5-1 μm.

21. The battery cell according to claim 1, characterized in that: The particle size distribution of the particles in the second positive electrode film layer is (Dv90-Dv10) / Dv50 of 2-20.

22. The battery cell according to claim 1, characterized in that: The particle size distribution (Dv90-Dv10) / Dv50 of the particles in the second positive electrode film layer is 7-16.

23. The battery cell according to claim 1, characterized in that: The specific surface area of ​​the particles in the second positive electrode film layer is 5-15cm 2 / g.

24. The battery cell according to claim 1, characterized in that The specific surface area of ​​the particles in the second positive electrode film layer is 8-13 cm 2 / g.

25. The battery cell according to claim 1, characterized in that The bonding strength between the positive electrode film layer and the positive electrode current collector is 56-141 N / m.

26. The battery cell according to claim 1, characterized in that: After the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets that leak current collectors accounts for 0.1%-5.7%.

27. The battery cell according to claim 1, characterized in that: After the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the number of positive electrode sheets that leak the current collector accounts for 0.1%-0.8%.

28. The battery cell according to any one of claims 1 to 27, characterized in that: When the battery cell is fully discharged, the compaction density of the positive electrode film layer is 2.3-2.5 g / cm 3 .

29. A battery device, characterized in that: Comprising the battery cell according to any one of claims 1-28.

30. An electrical device, characterized in that: The electrical device comprises the battery device as claimed in claim 29, and the battery device is used to provide electrical energy.

31. An energy storage device, characterized in that: The energy storage device comprises a battery device as claimed in claim 29, wherein the battery device is used to store electrical energy.

Images