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 arranged on the side close to the positive pole current collector and a second positive pole film layer arranged on the side, away from the positive pole current collector, of the first positive pole film layer; dv90 of particles in the second positive electrode film layer is greater than or equal to 18 microns; dv99 of particles in the first positive electrode film layer is smaller than or equal to 18 microns, a particle size volume distribution curve of the particles in the first positive electrode film layer presents bimodal distribution, and the peak position of a first peak is 0.1-1.5 microns. The battery monomer provided by the invention has good safety performance and energy density.

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 pursues battery capacity and safety performance, higher requirements are placed on battery energy density and safety performance. However, it is difficult for existing technologies to achieve simultaneous improvement of the above performances. How to balance the two has become a technical problem that urgently needs to be solved in this field. Summary of the invention

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

[0005] In a first aspect, the present application provides a battery cell, comprising a positive electrode plate, a negative electrode plate and an electrolyte; the positive electrode plate comprises a positive electrode collector and a positive electrode film layer arranged on at least one side of the positive electrode collector, the positive electrode film layer comprises a first positive electrode film layer arranged on the side close to the positive electrode collector and a second positive electrode film layer arranged on the side of the first positive electrode film layer away from the positive electrode collector, the Dv90 of the particles in the second positive electrode film layer is greater than or equal to 18 μm; the Dv99 of the particles in the first positive electrode film layer is less than or equal to 18 μm, and the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, wherein the peak position of the first peak is located at 0.1-1.5 μm.

[0006] The battery cell provided in the present application adds a first positive electrode film layer between the current collector and the second positive electrode film layer. Among them, the Dv90 of the particles in the second positive electrode film layer is greater than or equal to 18μm, and has certain large-sized particles to increase the compaction density of the positive electrode sheet and improve the energy density of the battery. However, the large particles in the second positive electrode film layer are easy to squeeze the current collector, causing burr problems. By setting a first positive electrode film layer with a Dv99 less than or equal to 18μm between the positive current collector and the second positive electrode film layer, the particles in the first positive electrode film layer are smaller in size than those in the second positive electrode film layer, which effectively reduces the probability of large particles in the second positive electrode film layer directly contacting and squeezing the current collector during the electrode sheet cutting process, thereby reducing the probability of burrs, improving the yield rate of electrode sheet cutting and the safety performance of the battery.

[0007] At the same time, the particle size volume distribution curve of the first positive electrode film layer particles of the battery cell in this application is set to present a bimodal distribution, and the particles are mainly concentrated in two particle size intervals with large differences. Smaller particles can effectively fill the gaps between larger particles, achieve close stacking of particles, and reduce the loss of compaction density of the positive electrode sheet caused by increasing the first positive electrode film layer. At the same time, the peak position of the first peak is located at 0.1-1.5μm, and the content of small particles in the first positive electrode film layer in contact with the current collector is increased, so that the surface is coated with more binder and the contact points with the current collector are increased, thereby improving the bonding force between the positive electrode film layer and the current collector, while improving the burr phenomenon and reducing the probability of the film layer being easy to fall off when the pole piece is cut, resulting in the current collector being exposed, and further improving the safety performance of the battery.

[0008] In any embodiment, the Dv90 of the particles in the second positive electrode film layer is 20-28 μm.

[0009] In any embodiment, the Dv99 of the particles in the first positive electrode film layer is 1-18 μm.

[0010] In any embodiment, the peak position of the first peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is 0.3-1 μm.

[0011] In any embodiment, the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 0.5-7 μm.

[0012] The peak positions of the two characteristic peaks of the particle size volume distribution of the particles in the first positive electrode film layer are controlled within the above range, that is, a large difference between the two particle size ranges is maintained, and smaller particles fill the gaps between larger particles. This can increase the gap filling rate between larger particles, thereby allowing the positive electrode plate to maintain a high compaction density and the battery cell to have a high energy density.

[0013] In any embodiment, the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 1-5 μm.

[0014] Furthermore, controlling the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer within the range of 1-5 μm helps to increase the specific surface area of ​​the larger particles in the first positive electrode film layer, increase the amount of surface binder coating, reduce the probability of collector leakage when the electrode sheet is cut, and improve the cycle performance of the battery; at the same time, the larger particle size in the first positive electrode film layer is within the above range, and the particle size is appropriate, which helps to maintain a high compaction density of the positive electrode film layer, and the battery has a high volume energy density.

[0015] In any embodiment, the first positive electrode film layer includes lithium-containing transition metal oxide single crystal particles and polyanion particles. The volume distribution particle size Dv50 of the lithium-containing transition metal oxide single crystal particles in the first positive electrode film layer is 0.5-7μm, and can be optionally 1-5μm. The volume distribution particle size Dv50 of the polyanion particles is 0.1-1.5μm, and can be optionally 0.3-1μm.

[0016] The size of lithium-containing transition metal oxide single crystal particles is smaller than that of polycrystalline particles, which can reduce the size of large particles in the first positive electrode film layer and reduce the probability of burrs on the positive electrode plate. However, due to the small single crystal particles in the first positive electrode film layer, the compaction density of the plate is reduced, thereby losing the volume energy density of the battery cell; at the same time, the smaller single crystal particles containing lithium transition metal oxide in the first positive electrode film layer have limited increase in the bonding force between the positive electrode film layer and the current collector, and the problem of powder loss and leakage of the current collector will still occur during the cutting process of the plate. In the embodiment of the present application, the first positive electrode film layer includes lithium-containing transition metal oxide single crystal particles and polyanion particles with smaller particle size. On the one hand, the polyanion particles fill the gaps between the single crystal particles to increase the compaction density of the plate; on the other hand, the polyanion is filled into the gaps between the single crystal particles, so that the number of particles in contact with the current collector of the first positive electrode film layer increases, the binder content and area increase, and the bonding strength between the positive electrode film layer and the current collector increases, further reducing the probability of leakage of the current collector and improving the yield rate of the plate.

[0017] In any embodiment, based on the total mass of the first positive electrode film layer, the mass proportion of the polyanion particles is 0.1%-10%.

[0018] The mass proportion of polyanions is in the range of 0.1%-10%, which helps to improve the volume energy density of battery cells; at the same time, compared with lithium-containing transition metal oxides, polyanions have a lower voltage platform and low-temperature voltage platform stability. The mass proportion of polyanions is in the above range, which helps to improve the power deterioration problem of the battery at low temperature and low SOC.

[0019] In any embodiment, based on the total mass of the first positive electrode film layer, the mass proportion of the polyanion particles is 2%-8%.

[0020] Furthermore, the mass proportion of polyanions is in the range of 2%-8%, which helps to further reduce the probability of collector leakage when the electrode is divided and improve the cycle performance of the battery; at the same time, the polyanion particles can fully fill the gaps between the lithium-containing transition metal oxide single crystal particles, while reducing the non-gap space occupied by excessive polyanion particles, thereby increasing the compaction density of the positive electrode film layer and further optimizing the energy density of the battery; in addition, the mass proportion of polyanions is in the above range, which helps to further improve the problem of power deterioration of the battery at low temperature and low SOC.

[0021] In any embodiment, the polyanionic particles include components 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.

[0022] In any embodiment, the polyanion includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate, lithium fluoro iron phosphate, lithium fluoro manganese iron phosphate and modified materials thereof.

[0023] Polyanions often have a smaller particle size, which is beneficial to filling the gaps in the first positive electrode film layer, and is beneficial to using its small particle size to increase the adhesive adhesion on the current collector, thereby improving the leakage of the current collector of the electrode.

[0024] In any embodiment, the polyanion includes one or more of lithium manganese iron phosphate and modified materials thereof.

[0025] Compared with other polyanions, lithium iron manganese phosphate has a higher voltage platform and a smaller voltage difference with lithium-containing transition metal oxides, which is conducive to the use of polyanion specific capacity, thereby further improving the volume energy density of battery cells. At the same time, polyanions can form voltage complementarity with lithium-containing transition metal oxides through their lower voltage platform, so that lithium-containing transition metal oxides can still maintain a higher voltage at low state of charge (SOC), effectively alleviating the power deterioration problem of lithium-containing transition metal oxide materials at low temperature and low SOC.

[0026] In any embodiment, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-6 μm, and the second peak is located at 5-14 μm.

[0027] In any embodiment, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-6 μm, and the second peak is located at 6-10 μm.

[0028] In any embodiment, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-5 μm, and the second peak is located at 6-10 μm.

[0029] In any embodiment, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-5 μm, and the second peak is located at 5-14 μm.

[0030] The particles in the second positive electrode film layer show a bimodal distribution, which is similar to the bimodal distribution of the particles in the first positive electrode film layer, which is conducive to smaller particles filling the gaps between larger particles, achieving close stacking of particles, and increasing the compaction density of the second positive electrode film layer, thereby further improving the energy density of the battery.

[0031] In any embodiment, the second positive electrode film layer includes lithium-containing transition metal oxide polycrystalline particles and lithium-containing transition metal oxide single crystal particles.

[0032] In any embodiment, the volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer is 20-30 μm.

[0033] In any embodiment, the volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer is 22-28 μm.

[0034] In any embodiment, the volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer is 5-14 μm.

[0035] In any embodiment, the volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer is 6-10 μm.

[0036] The Dv99 and Dv50 of the polycrystalline particles in the second positive electrode film layer are within the above ranges, and the particles have a larger size, which is beneficial to increasing the compaction density of the second positive electrode film layer, thereby further improving the energy density of the battery.

[0037] In any embodiment, the volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer is 6-13 μm.

[0038] In any embodiment, the volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer is 6-12 μm.

[0039] In any embodiment, the volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer is 1-6 μm.

[0040] In any embodiment, the volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer is 1-5 μm.

[0041] The combination of polycrystalline particles and single crystal particles that meet the above-mentioned particle size range is beneficial to improving the particle grading, achieving close stacking of particles in the positive electrode film layer, and further increasing the compaction density of the electrode sheet, thereby increasing the energy density of the battery.

[0042] In any embodiment, the mass ratio of the polycrystalline particles in the second positive electrode film layer to the single crystal particles in the second positive electrode film layer is 5:5-9:1.

[0043] Controlling the mass ratio of polycrystalline particles and single crystal particles to meet the above range and mixing single crystals with smaller particle sizes and polycrystalline particles with larger particle sizes can help improve the space utilization of the second positive electrode film layer, thereby increasing the compaction density of the electrode sheet and making the battery have excellent energy density.

[0044] In any embodiment, the mass ratio of the polycrystalline particles in the second positive electrode film layer to the single crystal particles in the second positive electrode film layer is 6:4-8:2.

[0045] The mass ratio of polycrystalline particles to single crystal particles in the second positive electrode film layer is in the range of 6:4-8:2, which is conducive to better grading between particles to further improve space utilization, increase the compaction density of the pole piece, and improve the volume energy density of the battery.

[0046] In any embodiment, the lithium-containing transition metal oxide in the positive electrode film layer includes nickel element. Based on the total molar number of transition metal in the lithium-containing transition metal oxide in the positive electrode film layer, the molar ratio of nickel element in the lithium-containing transition metal oxide in the positive electrode film layer is 80%-96%, and can be optionally 90%-96%.

[0047] Lithium-containing transition metal oxides with a molar proportion of 80%-96% nickel have high gram capacity, which is conducive to further improving the energy density of battery cells, but this will further increase the hardness of particles in the positive electrode film layer, increase the degree of compression of large particles in the positive electrode film layer on the current collector, and make it easy to generate burrs during the cutting process of the positive electrode sheet. The technical solution in the embodiment of the present application is particularly suitable for the positive electrode sheet, which further improves the high energy density of the battery while improving the yield rate during the cutting process of the electrode sheet, meeting the performance and efficiency requirements.

[0048] In any embodiment, the lithium-containing transition metal oxide in the first positive electrode film layer and the second positive electrode film layer independently comprises a component Li represented by the following general formula: a1 Ni x1 Co y1 M1 z1 M2 w1 O 2-b1, wherein M1 includes one or more of Mn and Al, M2 includes one or more of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K, 0.8≤a1≤1.2, 0≤x1≤1, 0≤y1≤1, 0≤z1≤1, 0≤w1≤0.1, and -0.1≤b1≤0.1.

[0049] In any embodiment, based on the total thickness of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 5%-50%, and can be optionally 20%-40%.

[0050] The thickness of the first positive electrode film layer is within the above range, which can reduce the contact between large particles in the second positive electrode film layer and the current collector, reduce the probability of burrs on the pole piece during cutting, and further improve the safety performance of the battery cell; at the same time, it reduces the pole piece compression loss caused by adding the first positive electrode film layer, while taking into account the energy density of the battery.

[0051] In any embodiment, the thickness of a single surface of the positive electrode film layer is 25-60 μm.

[0052] In any embodiment, the thickness of a single surface of the positive electrode film layer is 30-50 μm.

[0053] The thinning of the positive electrode film layer is beneficial to reducing the diffusion path of lithium ions and improving the dynamic performance of the battery cell; however, with the thinning of the positive electrode film layer, the compaction density of the pole piece increases, making the current collector more severely squeezed by large particles during cutting, and the probability of burrs is higher. At the same time, burrs are more likely to protrude from the edge of the positive electrode film layer, exacerbating the safety hazard of the burr problem.

[0054] In any embodiment, the bonding strength between the positive electrode film layer and the positive electrode current collector is 10-30 N / m.

[0055] In any embodiment, the bonding strength between the positive electrode film layer and the positive electrode current collector is 15-25 N / m.

[0056] 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.

[0057] 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%-2.5%.

[0058] 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%.

[0059] 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 burrs accounts for 0-2.1%.

[0060] 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 burrs accounts for 0-0.05%.

[0061] As the pole pieces become thinner and the compaction density increases, when the pole pieces are cut, large particles squeeze the current collector to produce burrs. In the embodiment of the present application, a first positive electrode film layer is added between the second positive electrode film layer and the current collector, and the number of pole pieces with burrs can be reduced to within the above range, which is beneficial to improving the yield of the pole pieces and improving the safety performance of the battery.

[0062] In any embodiment, the charge capacity of the positive electrode plate is 232-238.5 mAh g -1 .

[0063] In any embodiment, at -25°C, the time required to discharge the battery cell from 5% SOC to 0% SOC at a discharge rate of 5C is 41-65s.

[0064] At -25°C, the longer the time required to discharge the battery cell from 5% SOC to 0% SOC at a discharge rate of 5C, the better the power performance of the battery cell at low temperature and low SOC, and the more energy can be supplied at low power.

[0065] A second aspect of the present application provides a battery device, which includes the battery cell provided by the first aspect.

[0066] 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.

[0067] A fourth aspect of the present application provides an energy storage device, which includes the battery device provided by the second aspect, and the battery device is used to store electrical energy.

[0068] 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

[0069] 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.

[0070] Figure 1 It is a cross-sectional polishing electron microscope morphology image of a positive electrode piece in the prior art; Figure 2 This is a cross-sectional polished electron microscope morphology image of a pair of proportional positive electrode pieces of the present application; Figure 3 This is a cross-sectional polished electron microscope morphology image of a positive electrode sheet in one embodiment of the present application; Figure 4 It is a graph showing the test data of the bonding force of an electrode piece according to an embodiment of the present application and a pair of ratios; Figure 5 is a schematic diagram of a battery cell provided in some embodiments of the present application; Figure 6 is a schematic diagram of a battery module provided in some embodiments of the present application; Figure 7 is a schematic diagram of a battery pack provided in some embodiments of the present application; Figure 8 yes Figure 7 An exploded schematic diagram of a battery pack is shown; Fig. 9 is an exploded schematic diagram of a battery cell provided in some embodiments of the present application; Fig.10 It is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0071] In the drawings, the drawings are not necessarily drawn to scale.

[0072] Explanation of the reference numerals: 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

[0073] 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.

[0074] "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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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).

[0080] In the present application, the terms "plurality" and "multiple" refer to two or more.

[0081] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0082] 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.

[0083] 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.

[0084] 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 5 The battery cell 5 is a rectangular parallelepiped structure as an example.

[0085] 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 case and battery cells, and the battery cells or battery modules are accommodated in the case. In some embodiments, the case may serve as part of the chassis structure of the vehicle. For example, part of the case may become at least a part of the floor of the vehicle, or part of the case may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0086] In some embodiments, the battery may be an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0087] 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 6FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 6 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.

[0088] 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.

[0089] 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.

[0090] Figure 7 and Figure 8 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 7 and Figure 8 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.

[0091] The battery provided in the embodiment of the present application may include a lithium-ion battery.

[0092] 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.

[0093] 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).

[0094] In some embodiments, Fig. 9 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.

[0095] 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.

[0096] As the market's requirements for battery fast charging performance and energy density increase, the thickness of the pole piece after cold pressing is required to be reduced and the compaction density of the positive electrode film layer is increased. However, researchers found that this type of pole piece is prone to burrs when cutting, and the thickness of the positive electrode film layer cannot completely cover the burrs. In the electrode assembly, the pole piece with burrs can easily penetrate the diaphragm and cause the battery cell to self-discharge, and even cause the battery cell to short-circuit and fail, thereby affecting the safety performance of the battery and failing to meet the use requirements.

[0097] The first aspect of the present application provides a battery cell, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; Figure 3 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 arranged on the side close to the positive electrode collector 61 and a second positive electrode film layer 622 arranged on the side of the first positive electrode film layer 621 away from the positive electrode collector 61, the Dv90 of the particles in the second positive electrode film layer 622 is greater than or equal to 18μm; the Dv99 of the particles in the first positive electrode film layer 621 is less than or equal to 18μm, and the particle size volume distribution curve of the particles in the first positive electrode film layer 621 presents a bimodal distribution, wherein the peak position of the first peak is located at 0.1-1.5μm.

[0098] Studies have shown that the burrs generated during the slitting process of high compaction density pole pieces are 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 particle size of the particles in the pole piece to increase the compaction density of the pole piece. However, during the slitting process, the extrusion of the large particles by the cutter will be transmitted to the current collector, causing local deformation or even fracture of the current collector. The stress distribution at the fracture is uneven, which in turn generates burrs, such as Figure 1 As shown, it affects the safety performance of the battery.

[0099] 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, such as Figure 3As shown. Among them, the Dv90 of the particles in the second positive electrode film layer is greater than or equal to 18μm, and there are certain large-sized particles to increase the compaction density of the positive electrode sheet and improve the energy density of the battery. The large particles in the second positive electrode film layer are easy to squeeze the current collector, causing burr problems. By setting a first positive electrode film layer with a Dv99 of less than or equal to 18μm between the positive current collector and the second positive electrode film layer, the particles in the first positive electrode film layer are smaller in size than those in the second positive electrode film layer, which effectively reduces the probability of large particles in the second positive electrode film layer directly contacting and squeezing the current collector during the electrode sheet cutting process, thereby reducing the probability of burrs and improving the yield of electrode sheet cutting and the safety performance of the battery.

[0100] At the same time, the particle size volume distribution curve of the first positive electrode film layer particles of the battery cell in this application is set to present a bimodal distribution, and the particles are mainly concentrated in two particle size intervals with large differences. Smaller particles can effectively fill the gaps between larger particles, achieve close stacking of particles, and reduce the loss of compaction density of the positive electrode sheet caused by increasing the first positive electrode film layer. At the same time, the peak position of the first peak is located at 0.1-1.5μm, and the content of small particles in the first positive electrode film layer in contact with the current collector is increased, so that the surface is coated with more binder and the contact points with the current collector are increased, thereby improving the bonding force between the positive electrode film layer and the current collector, while improving the burr phenomenon and reducing the probability of the film layer being easy to fall off when the pole piece is cut, resulting in the current collector being exposed, and further improving the safety performance of the battery.

[0101] In some embodiments, Dv90 of the particles in the second positive electrode film layer may be 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, or any range of values ​​therebetween.

[0102] In some embodiments, the Dv90 of the particles in the second positive electrode film layer is 20-28 μm.

[0103] In some embodiments, Dv99 of the particles in the first positive electrode film layer can be selected to be 1 μm, 3 μm, 5 μm, 6 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or any range of values ​​therebetween.

[0104] In some embodiments, the Dv99 of the particles in the first positive electrode film layer is 1-18 μm.

[0105] In some embodiments, the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, wherein the peak position of the first peak is located at 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1 μm, 1.2 μm, 1.5 μm or any numerical range therebetween.

[0106] As used in this article, the term "burr" refers to the provisions of the IEEE1725 battery safety performance review and testing standard, such as Figure 1 As shown, the metal protrusion or warping extends outward from the current collector; the extension direction can be any direction, such as the thickness direction or the pole piece plane direction, and the reasons for its generation include but are not limited to cutting, tearing, etc.

[0107] As used herein, a bimodal distribution of a particle size volume distribution curve means that there are two characteristic peaks in the curve. This distribution characteristic indicates that the particles in the material are mainly concentrated in two particle size intervals with large differences.

[0108] As used herein, the particle size volume distribution curve presents a bimodal distribution, and the peak position of the first peak refers to the particle size corresponding to the smaller characteristic peak in the curve.

[0109] The Dv90 and Dv99 of particles are well known in the art, and respectively represent the particle sizes corresponding to when the cumulative volume distribution percentage of the particles reaches 90% and 99%.

[0110] The particle size volume distribution curve, Dv90 and Dv99 of the particles 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 from 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, setting 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, setting 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, setting 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.

[0111] It is worth noting that the materials used for testing in this application can be freshly prepared materials, or can be obtained by scraping powder from the film layer after disassembling the secondary battery.

[0112] In some embodiments, the peak position of the first peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is 0.3-1 μm.

[0113] In some embodiments, the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, wherein the peak position of the first peak is located at 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1 μm or any numerical range therebetween.

[0114] Furthermore, the peak position of the first peak of the particle size volume distribution curve of the particles in the first positive electrode film layer is controlled within the range of 0.3-1 μm, and the particles have a large specific surface area, which helps to reduce the probability of collector leakage caused by electrode sheet cutting. At the same time, the particle size is appropriate and the battery has good cycle performance.

[0115] In some embodiments, the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 0.5-7 μm.

[0116] In some embodiments, the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or any numerical range therebetween.

[0117] The peak positions of the two characteristic peaks of the particle size volume distribution of the particles in the first positive electrode film layer are controlled within the above range, that is, a large difference between the two particle size ranges is maintained, and smaller particles fill the gaps between larger particles. This can increase the gap filling rate between larger particles, thereby allowing the positive electrode plate to maintain a high compaction density and the battery cell to have a high energy density.

[0118] In some embodiments, the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 1-5 μm.

[0119] In some embodiments, the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any numerical range therebetween.

[0120] Furthermore, controlling the peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer within the range of 1-5 μm helps to increase the specific surface area of ​​the larger particles in the first positive electrode film layer, increase the amount of surface binder coating, reduce the probability of collector leakage when the electrode sheet is cut, and improve the cycle performance of the battery; at the same time, the larger particle size in the first positive electrode film layer is within the above range, and the particle size is appropriate, which helps to maintain a high compaction density of the positive electrode film layer, and the battery has a high volume energy density.

[0121] In some embodiments, the first positive electrode film layer includes lithium-containing transition metal oxide single crystal particles and polyanion particles. The volume distribution particle size Dv50 of the lithium-containing transition metal oxide single crystal particles in the first positive electrode film layer is 0.5-7μm, and can be optionally 1-5μm. The volume distribution particle size Dv50 of the polyanion particles is 0.1-1.5μm, and can be optionally 0.3-1μm.

[0122] In some embodiments, the volume distribution particle size Dv50 of the lithium-containing transition metal oxide single crystal particles in the first positive electrode film layer can be selected as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm or any two of the numerical ranges.

[0123] In some embodiments, the volume distribution particle size Dv50 of the polyanion particles in the first positive electrode film layer can be selected as 0.1μm, 0.2μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm or any two of the numerical ranges.

[0124] As used herein, the term "single crystal particle" refers to the smallest unit of a particle within a certain observation range. The interior of a single crystal particle may include any form of defects, but no smaller particles can be defined therein. It is understood that the single crystal particle described herein does not necessarily mean that there is no grain boundary inside the single crystal, and that atoms, molecules or ions are continuously and consistently arranged periodically in three-dimensional space, but refers to the fact that no smaller particles can be defined by grain boundaries inside the single crystal at a certain observation scale.

[0125] As used herein, the term "polyanionic" particles refers to particles whose crystal structure contains a plurality of anions (e.g. etc.) through oxygen atom bridging to form a stable three-dimensional framework structure.

[0126] The Dv50 of a particle is a well-known meaning in the art, which indicates the particle size corresponding to when the cumulative volume distribution percentage of the particle reaches 50%. The Dv50 of a particle can be determined by referring to the test method of the Dv90 of a particle.

[0127] Lithium-containing transition metal oxides are an important class of positive electrode materials for lithium-ion batteries, characterized by transition metals (such as cobalt, nickel, manganese, etc.) combined with oxygen to form a layered or spinel structure. As examples, they include but are not limited to: lithium cobalt oxide, lithium nickel oxide, ternary material lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium-rich manganese-based oxides.

[0128] The size of lithium-containing transition metal oxide single crystal particles is smaller than that of polycrystalline particles, which can reduce the size of large particles in the first positive electrode film layer and reduce the probability of burrs on the positive electrode plate. However, due to the small single crystal particles in the first positive electrode film layer, the compaction density of the plate is reduced, thereby losing the volume energy density of the battery cell; at the same time, the smaller single crystal particles containing lithium transition metal oxide in the first positive electrode film layer have limited increase in the bonding force between the positive electrode film layer and the current collector, and the problem of powder loss and leakage of the current collector will still occur during the cutting process of the plate. In the embodiment of the present application, the first positive electrode film layer includes lithium-containing transition metal oxide single crystal particles and polyanion particles with smaller particle size. On the one hand, the polyanion particles fill the gaps between the single crystal particles to increase the compaction density of the plate; on the other hand, the polyanion is filled into the gaps between the single crystal particles, so that the number of particles in contact with the current collector of the first positive electrode film layer increases, the binder content and area increase, and the bonding strength between the positive electrode film layer and the current collector increases, further reducing the probability of leakage of the current collector and improving the yield rate of the plate.

[0129] In some embodiments, based on the total mass of the first positive electrode film layer, the mass proportion of the polyanion particles is 0.1%-10%.

[0130] In some embodiments, the mass proportion of the polyanion particles based on the total mass of the first positive electrode film layer can be selected to be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10% or any numerical range therebetween.

[0131] The mass proportion of polyanions is in the range of 0.1%-10%, which helps to improve the volume energy density of battery cells; at the same time, compared with lithium-containing transition metal oxides, polyanions have a lower voltage platform and low-temperature voltage platform stability. The mass proportion of polyanions is in the above range, which helps to improve the power deterioration problem of the battery at low temperature and low SOC.

[0132] In some embodiments, based on the total mass of the first positive electrode film layer, the mass proportion of the polyanion particles is 2%-8%.

[0133] Furthermore, the mass proportion of polyanions is in the range of 2%-8%, which helps to further reduce the probability of collector leakage when the electrode is divided and improve the cycle performance of the battery; at the same time, the polyanion particles can fully fill the gaps between the lithium-containing transition metal oxide single crystal particles, while reducing the non-gap space occupied by excessive polyanion particles, thereby increasing the compaction density of the positive electrode film layer and further optimizing the energy density of the battery; in addition, the mass proportion of polyanions is in the above range, which helps to further improve the problem of power deterioration of the battery at low temperature and low SOC.

[0134] In some embodiments, the polyanionic particles include components represented by the following 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] In some embodiments, the polyanion includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate, lithium fluoro iron phosphate, lithium fluoro manganese iron phosphate and modified materials thereof.

[0144] Polyanions often have a smaller particle size, which is beneficial to filling the gaps in the first positive electrode film layer, and is beneficial to using its small particle size to increase the adhesive adhesion on the current collector, thereby improving the leakage of the current collector of the electrode.

[0145] In some embodiments, the polyanion includes one or more of lithium manganese iron phosphate and modified materials thereof.

[0146] Compared with other polyanions, lithium iron manganese phosphate has a higher voltage platform and a smaller voltage difference with lithium-containing transition metal oxides, which is conducive to the use of polyanion specific capacity, thereby further improving the volume energy density of battery cells. At the same time, polyanions can form voltage complementarity with lithium-containing transition metal oxides through their lower voltage platform, so that lithium-containing transition metal oxides can still maintain a higher voltage at low state of charge (SOC), effectively alleviating the power deterioration problem of lithium-containing transition metal oxide materials at low temperature and low SOC.

[0147] In some embodiments, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-6 μm, and the second peak is located at 5-14 μm.

[0148] In some embodiments, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-6 μm, and the second peak is located at 6-10 μm.

[0149] In some embodiments, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-5 μm, and the second peak is located at 6-10 μm.

[0150] In some embodiments, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, wherein the first peak of the bimodal distribution is located at 1-5 μm, and the second peak is located at 5-14 μm.

[0151] In some embodiments, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, and the first peak of the bimodal distribution can be located at 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm or any numerical range therebetween.

[0152] In some embodiments, the particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, and the second peak of the bimodal distribution can be located at 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11 μm, 12μm, 14μm or any numerical range therebetween.

[0153] The particles in the second positive electrode film layer show a bimodal distribution, which is similar to the bimodal distribution of the particles in the first positive electrode film layer, which is conducive to smaller particles filling the gaps between larger particles, achieving close stacking of particles, and increasing the compaction density of the second positive electrode film layer, thereby further improving the energy density of the battery.

[0154] In some embodiments, the second positive electrode film layer includes lithium-containing transition metal oxide polycrystalline particles and lithium-containing transition metal oxide single crystal particles.

[0155] When used in this article, the term "polycrystalline particles" refers to agglomerates of single crystal particles. The agglomeration here is a hard agglomeration caused by chemical bonding of single crystal particles, which makes the polycrystalline particles have more clear grain boundaries and inconsistent atomic arrangement orientation. After cutting the cross section of the polycrystalline particles, it can be seen that the polycrystalline particles are formed by the agglomeration of many single crystal particles.

[0156] In some embodiments, the volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer is 20-30 μm.

[0157] In some embodiments, the volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer is 22-28 μm.

[0158] In some embodiments, the volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer can be selected as 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm or any numerical range therebetween.

[0159] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer is 5-14 μm.

[0160] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer is 6-10 μm.

[0161] In some embodiments, the volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer can be selected to be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or any numerical range therebetween.

[0162] The Dv99 and Dv50 of the polycrystalline particles in the second positive electrode film layer are within the above ranges, and the particles have a larger size, which is beneficial to increasing the compaction density of the second positive electrode film layer, thereby further improving the energy density of the battery.

[0163] In some embodiments, the volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer is 6-13 μm.

[0164] In some embodiments, the volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer is 6-12 μm.

[0165] In some embodiments, the volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm or any numerical range therebetween.

[0166] In some embodiments, the volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer is 1-6 μm.

[0167] In some embodiments, the volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer is 1-5 μm.

[0168] In some embodiments, the volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm or any numerical range therebetween.

[0169] The combination of polycrystalline particles and single crystal particles that meet the above-mentioned particle size range is beneficial to improving the particle grading, achieving close stacking of particles in the positive electrode film layer, and further increasing the compaction density of the electrode sheet, thereby increasing the energy density of the battery.

[0170] In some embodiments, the mass ratio of the polycrystalline particles in the second positive electrode film layer to the single crystal particles in the second positive electrode film layer is 5:5-9:1.

[0171] As used herein, the mass ratio of polycrystalline particles to single crystal particles in the second positive electrode film layer may be selected as 5:5, 5.5:4.5, 6:4, 6.5:3.5, 7:3, 7.5:2.5, 8:2, 8.5:1.5, 9:1 or any value therebetween.

[0172] When used in this article, the mass proportion of polycrystalline particles and single crystal particles in the second positive electrode film layer can be determined by the following method: 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 have two types of particles with large differences in particle size. This layer is the first positive electrode film layer; the film layer particles away from the positive electrode current collector side are larger, and this layer is the second positive electrode film layer. Randomly select a number of points in the second positive electrode film layer for shooting, and the number of points is ≥10, which can be 10, 20, 50, 100, etc. Calculate the area ratio of the size of the positive electrode film layer occupied by polycrystalline particles and single crystal particles in the photographed picture, and calculate the average value. The area ratio between polycrystalline particles and single crystal particles can be equivalent to the mass ratio of polycrystalline particles to single crystal particles.

[0173] Controlling the mass ratio of polycrystalline particles and single crystal particles to meet the above range and mixing single crystals with smaller particle sizes and polycrystalline particles with larger particle sizes can help improve the space utilization of the second positive electrode film layer, thereby increasing the compaction density of the electrode sheet and making the battery have excellent energy density.

[0174] In some embodiments, the mass ratio of the polycrystalline particles in the second positive electrode film layer to the single crystal particles in the second positive electrode film layer is 6:4-8:2.

[0175] The mass ratio of polycrystalline particles to single crystal particles in the second positive electrode film layer is in the range of 6:4-8:2, which is conducive to better grading between particles to further improve space utilization, increase the compaction density of the pole piece, and improve the volume energy density of the battery.

[0176] In some embodiments, the lithium-containing transition metal oxide in the positive electrode film layer includes nickel element. Based on the total molar number of transition metals in the lithium-containing transition metal oxide in the positive electrode film layer, the molar ratio of nickel element in the lithium-containing transition metal oxide in the positive electrode film layer is 80%-96%, and can be optionally 90%-96%.

[0177] In some embodiments, the lithium-containing transition metal oxide in the positive electrode film layer includes nickel element. Based on the total molar number of transition metal in the lithium-containing transition metal oxide in the positive electrode film layer, the molar proportion of nickel element in the lithium-containing transition metal oxide in the positive electrode film layer can be selected to be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96% or any numerical range therebetween.

[0178] When used in this article, based on the total molar number of transition metals in the lithium-containing transition metal oxide, the molar proportion of nickel in the lithium-containing transition metal oxide can be determined by instruments and methods known in the art. As an example, it can be measured by the following method: take 0.5g of the material to be tested, soak it in 100 mL of aqua regia solution for digestion, the digestion temperature is 50°C, and then take the completely dissolved solution for inductively coupled plasma (ICP) testing to detect the content of transition metals (such as Ni, Co, Mn ions) in the solution, and divide the molar number of nickel elements by the total molar number of transition metal elements as the molar proportion of nickel elements in the lithium-containing transition metal oxide based on the total molar number of transition metals in the lithium-containing transition metal oxide.

[0179] Lithium-containing transition metal oxides with a molar proportion of 80%-96% nickel have high gram capacity, which is conducive to further improving the energy density of battery cells, but this will further increase the hardness of particles in the positive electrode film layer, increase the degree of compression of large particles in the positive electrode film layer on the current collector, and make it easy to generate burrs during the cutting process of the positive electrode sheet. The technical solution in the embodiment of the present application is particularly suitable for the positive electrode sheet, which further improves the high energy density of the battery while improving the yield rate during the cutting process of the electrode sheet, meeting the performance and efficiency requirements.

[0180] In some embodiments, the lithium-containing transition metal oxide in the first positive electrode film layer and the second positive electrode film layer each independently comprises a component Li represented by the following general formula: a1 Ni x1 Co y1 M1 z1 M2 w1 O 2-b1, wherein M1 includes one or more of Mn and Al, M2 includes one or more of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K, 0.8≤a1≤1.2, 0≤x1≤1, 0≤y1≤1, 0≤z1≤1, 0≤w1≤0.1, and -0.1≤b1≤0.1.

[0181] In some embodiments, a1 may be selected to be 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2 or any range therebetween.

[0182] In some embodiments, x1 may 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, or any range therebetween.

[0183] In some embodiments, y1 may 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, or any range therebetween.

[0184] In some embodiments, z1 can be selected as 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 or any range therebetween.

[0185] In some embodiments, w1 may be selected to be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any range therebetween.

[0186] In some embodiments, b1 may be selected to be -0.1, -0.05, 0, 0.05, 0.1, or any range therebetween.

[0187] When the positive electrode film layer includes the above-mentioned type of lithium-containing transition metal oxide, the gram capacity of the positive electrode active material can be further increased, thereby further improving the energy density of the battery cell.

[0188] In some embodiments, based on the total thickness of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 5%-50%, and can be optionally 20%-40%.

[0189] The thickness ratio of the first positive electrode film layer can be tested by methods and equipment known in the art, as shown below: 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 close to the current collector has a smaller particle size and has two types of particles with large differences in particle size. This layer is the first positive electrode film layer; the film layer away from the positive current collector has larger particles, which is the second positive electrode film layer. Mark the interface between the first positive electrode film layer and the second positive electrode film layer, and the vertical H1 distance from the interface to the positive current collector is the thickness of the first positive electrode film layer. The vertical H2 distance from the surface of the second positive electrode film layer away from the current collector to the current collector is the single-sided thickness of the positive electrode film layer. The thickness ratio of the first positive electrode film layer is H1 / H2.

[0190] In some embodiments, based on the total thickness of the positive electrode film layer, the thickness ratio of the first positive electrode film layer may be selected to be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any numerical range therebetween.

[0191] The thickness of the first positive electrode film layer is within the above range, which can reduce the contact between large particles in the second positive electrode film layer and the current collector, reduce the probability of burrs on the pole piece during cutting, and further improve the safety performance of the battery cell; at the same time, it reduces the pole piece compression loss caused by adding the first positive electrode film layer, while taking into account the energy density of the battery.

[0192] In some embodiments, the single-side thickness of the positive electrode film layer is 25-60 μm.

[0193] In some embodiments, the single-side thickness of the positive electrode film layer is 30-50 μm.

[0194] In some embodiments, the thickness of the positive electrode film layer may be 25 μm, 30 μm, 40 μm, 50 μm, 60 μm, or any range therebetween.

[0195] The thinning of the positive electrode film layer is beneficial to reducing the diffusion path of lithium ions and improving the dynamic performance of the battery cell; however, with the thinning of the positive electrode film layer, the compaction density of the pole piece increases, making the current collector more severely squeezed by large particles during cutting, and the probability of burrs is higher. At the same time, burrs are more likely to protrude from the edge of the positive electrode film layer, exacerbating the safety hazard of the burr problem.

[0196] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector is 10-30 N / m.

[0197] In some embodiments, the bonding strength between the positive electrode film layer and the positive electrode current collector is 15-25 N / m.

[0198] 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.

[0199] 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.

[0200] 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%-2.5%.

[0201] 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%-0.8%.

[0202] In some embodiments, the percentage of positive electrode plates with leaking current collectors can be selected as 0.1%, 0.2%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.7%, 0.75%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 18%, 2%, 2.15%, 2.35%, 2.5% or any numerical range therebetween.

[0203] 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%.

[0204] 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 burrs accounts for 0-2.1%.

[0205] 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 burrs accounts for 0-0.05%.

[0206] In some embodiments, after the positive electrode sheets are cut at a cutting speed of 0.5 m / s, the proportion of positive electrode sheets with burrs can be selected as 0, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.1% or any numerical range therebetween.

[0207] As used herein, a positive electrode sheet with burrs refers to a positive electrode sheet after slitting, and the size of the burrs on the sheet is calibrated. Burrs with a size greater than or equal to 40% of the thickness of the positive electrode sheet are included in the statistical range and calibrated as positive electrode sheets with burrs. The proportion of positive electrode sheets with burrs can be tested by methods known in the art. As an example, the following method can be used for testing: using the burr size measurement method as described above to observe a certain number of slit sheets through CCD, counting the frequency K1 of the sheets with burrs, and calculating the proportion of the sheets with burrs as K1 / total number of sheets × 100%.

[0208] When used in this article, the term "burr size" refers to the absolute length of the burr (not limited to the vertical distance). The burr size can be tested using instruments and methods known in the art. As an example, the following method can be used for testing: use a CCD instrument to observe the burrs after cutting (such as Keyence 600), the test temperature is 25°C, the test electrode size is 80mm×60mm, the magnification is 300x, the light intake opening is 30%, and the burr size is calibrated.

[0209] As the pole pieces become thinner and the compaction density increases, when the pole pieces are cut, large particles squeeze the current collector to produce burrs. In the embodiment of the present application, a first positive electrode film layer is added between the second positive electrode film layer and the current collector, and the number of pole pieces with burrs can be reduced to within the above range, which is beneficial to improving the yield of the pole pieces and improving the safety performance of the battery.

[0210] In some embodiments, the charge capacity of the positive electrode is 232-238.5 mAh g -1 .

[0211] In some embodiments, the charge capacity of the positive electrode sheet can be 232 mAh g -1 , 233 mAh g -1, 233.7mAh g -1 , 234 mAh g -1 , 234.5 mAh g -1 , 235 mAh g -1 、235.5 mAh g -1 , 236 mAh g -1 、236.5 mAhg -1 、237 mAh g -1 、237.3 mAh g -1 , 238mAh g -1 , 238.5 mAh g -1 Or any range of values ​​in between.

[0212] When used herein, the charge gram capacity of the positive electrode sheet can be tested using methods and instruments known in the art, and the specific examples are as follows: a button cell is prepared according to the preparation method in the embodiment of the present application. At 25°C, the button cell prepared above is left to stand for 3 hours, charged to 4.25V at a constant current of 0.1C, then charged to 50μΑ at a constant voltage, left to stand for 5 minutes, and the charge capacity of the button cell at 25°C is recorded. The charge gram capacity of the positive electrode active material at 25°C Cl = the charge capacity of the button cell at 25°C / the mass of the positive electrode active material.

[0213] In some embodiments, at -25°C, the time required to discharge the battery cell from 5% SOC to 0% SOC at a discharge rate of 5C is 41-65s.

[0214] In some embodiments, at -25°C, the time required to discharge a battery cell from 5% SOC to 0% SOC at a discharge rate of 5C may be selected as 41s, 42s, 43s, 44s, 45s, 46s, 47s, 48s, 49s, 50s, 51s, 52s, 53s, 54s, 55s, 56s, 57s, 58s, 59s, 60s, 61s, 62s, 63s, 64s, 65s or any range of values ​​therebetween.

[0215] As used herein, the time required to discharge a battery cell from 5% SOC to 0% SOC at a discharge rate of 5C at -25°C can be tested using methods and instruments known in the art. The battery cell is left at -25°C for 2 hours to ensure that the temperature of the battery cell is -25°C. The battery is discharged at a discharge rate of 5C to 5% SOC and the timing starts. The discharge is continued at a rate of 5C until the discharge voltage is less than 2.8V and the timing is stopped. The battery is considered to have been discharged to 0% SOC. The timing duration T is the time required to discharge a battery cell from 5% SOC to 0% SOC at a discharge rate of 5C at -25°C.

[0216] At -25°C, the longer the time required to discharge the battery cell from 5% SOC to 0% SOC at a discharge rate of 5C, the better the power performance of the battery cell at low temperature and low SOC, and the more energy can be supplied at low power.

[0217] Battery device The embodiment of the present application also provides a battery device, and the battery device includes the battery cell provided by the embodiment of the present application.

[0218] The battery device includes one or more of a battery module, a battery pack, and an energy storage battery.

[0219] 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.

[0220] 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.

[0221] 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.

[0222] Fig.10 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.

[0223] 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.

[0224] 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.

[0225] 1. Preparation method Example 1 (1) Preparation of positive electrode Preparation of the first positive electrode film slurry: LiNi 0.92 Co 0.04 Mn 0.04 O2 single crystal, LiMn 0.3 Fe 0.7 PO4, conductive carbon, and binder PVDF are dissolved in NMP (N-methylpyrrolidone) solvent in a mass ratio of 95:3:1:1, fully stirred and mixed, and then wetted, kneaded and dispersed to obtain the first film layer positive electrode slurry.

[0226] Preparation of the second cathode film slurry: LiNi 0.92 Co 0.04 Mn 0.04 O2 polycrystalline, LiNi 0.92 Co 0.04 Mn 0.04 O2 single crystal, conductive carbon, and binder PVDF are dissolved in NMP (N-methylpyrrolidone) solvent in a weight ratio of 68.6:29.4:1:1, fully stirred and mixed, and then wetted, kneaded and dispersed to obtain the second film layer positive electrode slurry.

[0227] 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.

[0228] Among them, in the second positive electrode film layer, the Dv99 of polycrystalline particles is 25μm, and the Dv50 is 7μm; the Dv99 of single crystal particles is 12μm, and the Dv50 is 2.5μm; the mass ratio of polycrystalline particles to single crystal particles is 7:3; the particle size in the second positive electrode film layer is a bimodal distribution, with the first peak at 2.5μm and the second peak at 7μm. The bonding strength between the positive electrode film layer and the current collector is 23N / m; the single-sided thickness of the positive electrode film layer is 50μm; the charge gram capacity of the positive electrode plate is 237.5mAh / g.

[0229] (2) Preparation of negative electrode The negative electrode active material graphite, binder (polyvinyl alcohol), and conductive agent SP-Li are mixed in a mass ratio of 90:5:5, and deionized water solvent 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.

[0230] (3) Preparation of electrolyte In an argon atmosphere glove box (H2O<0.1ppm, O2<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, a certain amount of LiPF6 lithium salt was dissolved in the organic solvent, the concentration of the lithium salt was controlled to be 1 mol / L, and stirred evenly to obtain an electrolyte.

[0231] (4) Isolation film Polyethylene film with a thickness of 13 μm.

[0232] (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.

[0233] Example 2-3 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the Dv99 of the first positive electrode film layer is different, see Table 1 for details.

[0234] Embodiment 4-6 The preparation method of the lithium ion battery is similar to that of Example 1, except that the LiNi 0.92 Co 0.04 Mn 0.04 The Dv50 of O2 single crystal is different, see Table 1 for details.

[0235] Embodiment 7-9 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiMn 0.3 Fe 0.7 The Dv50 of PO4 is different, see Table 1 for details.

[0236] Example 10 The preparation method of the lithium ion battery is similar to that of Example 1, except that the LiNi 0.92 Co 0.04 Mn 0.04 O2 single crystal, LiMn0.3 Fe 0.7 The mass ratio of PO4, conductive carbon and binder PVDF is 97:1:1:1, see Table 1 for details.

[0237] Embodiment 11 The preparation method of the lithium ion battery is similar to that of Example 1, except that the LiNi 0.92 Co 0.04 Mn 0.04 O2 single crystal, LiMn 0.3 Fe 0.7 The mass ratio of PO4, conductive carbon and binder PVDF is 93:5:1:1, see Table 1 for details.

[0238] Example 12 The preparation method of the lithium ion battery is similar to that of Example 1, except that the LiNi 0.92 Co 0.04 Mn 0.04 O2 single crystal, LiMn 0.3 Fe 0.7 The mass ratio of PO4, conductive carbon and binder PVDF is 90:8:1:1, see Table 1 for details.

[0239] Embodiment 13 The preparation method of the lithium ion battery is similar to that of Example 1, except that the LiNi 0.92 Co 0.04 Mn 0.04 O2 single crystal, LiMn 0.3 Fe 0.7 The mass ratio of PO4, conductive carbon and binder PVDF is 88:10:1:1, see Table 1 for details.

[0240] Embodiment 14 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the thickness of the first positive electrode film layer is 8 μm. Based on the total thickness of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 16.7%, see Table 1 for details.

[0241] Embodiment 15 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the LiMn 0.3 Fe 0.7 PO4 was replaced by LiFePO4, see Table 1 for details.

[0242] 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 include the first positive electrode film layer, see Table 1 for details.

[0243] Comparative Example 2 The preparation method of the lithium ion battery is similar to that of Example 1, except that the first positive electrode film layer does not contain LiMn 0.3 Fe 0.7 PO4, LiNi in the first positive electrode slurry 0.92 Co 0.04 Mn 0.04 The mass ratio of O2 single crystal, conductive carbon and binder PVDF is 98:1:1:1, see Table 1 for details.

[0244] Comparative Example 3 The preparation method of the lithium-ion battery is similar to that of Example 1, except that the Dv99 of the first positive electrode film layer is different, see Table 1 for details.

[0245] 2. Performance Test 1. Battery volume energy density test Let the lithium-ion secondary battery stand at 25°C for 2 hours, ensuring that the temperature of the lithium-ion secondary battery is 25°C. After charging the lithium-ion secondary battery at 0.33C at 25°C to a charge cut-off voltage of 4.25V, continue to charge at a constant voltage at the charge cut-off voltage until the current is 0.05C and the charge is cut off (where C represents the rated capacity of the lithium-ion secondary battery). After letting the lithium-ion secondary battery stand at 25°C for 1 hour, discharge the lithium-ion secondary battery at 0.33C at 25°C to a discharge cut-off voltage of 2.8V, and record the total discharge energy of the lithium-ion secondary battery 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.

[0246] 2. Cycle capacity retention rate At 25°C, charge the battery to 4.25V at a charge rate of 0.33C of the nominal capacity, then charge at a constant voltage of 4.25V to 0.05C, let stand for 10 minutes, then discharge to 2.8V at a discharge rate of 1C, let stand for 10 minutes. The above charge and discharge is one cycle. Based on the total capacity of the nominal capacity, the percentage of battery capacity after 1000 cycles is recorded as the capacity retention rate.

[0247] 3. Test Results The test results of the above embodiments and comparative examples are shown in Tables 1 to 7.

[0248] Table 1

[0249] Table 2

[0250] From the comparison between the embodiment and the comparative example, it can be seen that the positive electrode film layer includes a first positive electrode film layer arranged 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, the Dv90 of the particles in the second positive electrode film layer is greater than or equal to 18μm, the Dv99 of the particles in the first positive electrode film layer is less than or equal to 18μm, and the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, wherein the peak position of the first peak is located at 0.1-1.5μm, which is beneficial to reduce the burrs generated by the electrode during the cutting process, improve the yield rate of the electrode cutting and the safety performance of the battery, and at the same time reduce the probability of the positive electrode film layer falling off during the cutting process and causing the current collector to be exposed.

[0251] Table 3

[0252] From the comparison between Example 1 and Example 5 and Example 4 and Example 6, it can be seen that the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, and the second peak in the bimodal distribution is located in the range of 1-5 μm, which helps to further reduce the probability of collector leakage caused by pole piece cutting, while improving the volume energy density of the battery and taking into account the cycle performance.

[0253] Table 4

[0254] From the comparison between Example 1, Example 8, Example 7 and Example 9, it can be seen that the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, and the first peak in the bimodal distribution is located in the range of 0.3-1 μm, which helps to reduce the probability of collector leakage caused by pole piece cutting, while improving the volume energy density of the battery.

[0255] Table 5

[0256] From the comparison between Example 1, Example 11 and Example 10, and Examples 11-12, it can be seen that based on the total mass of the first positive electrode film layer, the mass of the polyanion particles accounts for 2%-8%, which helps to reduce the probability of collector leakage caused by pole piece cutting, while taking into account the volume energy density of the battery, the cycle performance of the battery, and the power performance of the battery at low temperature and low SOC.

[0257] Table 6

[0258] From the comparison between Example 1 and Example 14, it can be seen that based on the total thickness of the positive electrode film layer, the thickness of the first positive electrode film layer accounts for 20%-40%, which helps to further reduce the probability of burrs after the electrode sheet is cut, and at the same time improve the cycle performance and low-temperature power performance of the battery.

[0259] Table 7

[0260] From the comparison between Example 1 and Example 15, it can be seen that the polyanion includes lithium manganese iron phosphate, which helps to further increase the charging capacity of the positive electrode plate, improve the power performance at low SOC, and increase the volume energy density of the battery.

[0261] 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 disposed on a side close to the positive electrode current collector and a second positive electrode film layer disposed on a side of the first positive electrode film layer away from the positive electrode current collector. The Dv90 of the particles in the second positive electrode film layer is greater than or equal to 18 μm; The Dv99 of the particles in the first positive electrode film layer is less than or equal to 18 μm, and the particle size volume distribution curve of the particles in the first positive electrode film layer presents a bimodal distribution, wherein the peak position of the first peak is located at 0.1-1.5 μm.

2. The battery cell according to claim 1, characterized in that: The Dv90 of the particles in the second positive electrode film layer is 20-28 μm.

3. The battery cell according to claim 1, characterized in that: The Dv99 of the particles in the first positive electrode film layer is 1-18 μm.

4. The battery cell according to claim 1, characterized in that: The peak position of the first peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is 0.3-1 μm.

5. The battery cell according to claim 1, characterized in that: The peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 0.5-7 μm.

6. The battery cell according to claim 1, characterized in that: The peak position of the second peak in the particle size volume distribution curve of the particles in the first positive electrode film layer is located at 1-5 μm.

7. The battery cell according to claim 1, characterized in that: The first positive electrode film layer includes lithium-containing transition metal oxide single crystal particles and polyanion particles. The volume distribution particle size Dv50 of the lithium-containing transition metal oxide single crystal particles in the first positive electrode film layer is 0.5-7 μm.

8. The battery cell according to claim 7, characterized in that: The volume distribution particle size Dv50 of the lithium-containing transition metal oxide single crystal particles in the first positive electrode film layer is 1-5 μm.

9. The battery cell according to claim 7, characterized in that: The volume distribution particle size Dv50 of the polyanion particles is 0.1-1.5 μm.

10. The battery cell according to claim 7, characterized in that: The volume distribution particle size Dv50 of the polyanion particles is 0.3-1 μm.

11. The battery cell according to claim 7, characterized in that: Based on the total mass of the first positive electrode film layer, the mass proportion of the polyanion particles is 0.1%-10%.

12. The battery cell according to claim 7, characterized in that: Based on the total mass of the first positive electrode film layer, the mass proportion of the polyanion particles is 2%-8%.

13. The battery cell according to claim 7, characterized in that: The polyanion particles include components shown in 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.

14. The battery cell according to claim 7, characterized in that: The polyanion includes one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium fluoride phosphate, lithium manganese iron phosphate, lithium fluoride phosphate, lithium iron manganese fluoride phosphate and modified materials thereof.

15. The battery cell according to claim 7, characterized in that: The polyanion includes one or more of lithium manganese iron phosphate and modified materials thereof.

16. The battery cell according to claim 1, characterized in that: The particle size volume distribution curve of the particles in the second positive electrode film layer presents a bimodal distribution, and the peak position of the first peak in the particle size volume distribution curve of the particles in the second positive electrode film layer is located at 1-6 μm.

17. The battery cell according to claim 16, characterized in that: The peak position of the first peak in the particle size volume distribution curve of the particles in the second positive electrode film layer is located at 1-5 μm.

18. The battery cell according to claim 16, characterized in that: The peak position of the second peak in the particle size volume distribution curve of the particles in the second positive electrode film layer is located at 5-14 μm.

19. The battery cell according to claim 16, characterized in that: The peak position of the second peak in the particle size volume distribution curve of the particles in the second positive electrode film layer is located at 6-10 μm.

20. The battery cell according to claim 1, characterized in that The second positive electrode film layer includes lithium-containing transition metal oxide polycrystalline particles and lithium-containing transition metal oxide single crystal particles.

21. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer is 20-30 μm.

22. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv99 of the polycrystalline particles in the second positive electrode film layer is 22-28 μm.

23. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer is 5-14 μm.

24. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv50 of the polycrystalline particles in the second positive electrode film layer is 6-10 μm.

25. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer is 6-13 μm.

26. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv99 of the single crystal particles in the second positive electrode film layer is 6-12 μm.

27. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer is 1-6 μm.

28. The battery cell according to claim 20, characterized in that: The volume distribution particle size Dv50 of the single crystal particles in the second positive electrode film layer is 1-5 μm.

29. The battery cell according to claim 20, characterized in that: The mass ratio of the polycrystalline particles in the second positive electrode film layer to the single crystal particles in the second positive electrode film layer is 5:5-9:

1.

30. The battery cell according to claim 20, characterized in that The mass ratio of the polycrystalline particles in the second positive electrode film layer to the single crystal particles in the second positive electrode film layer is 6:4-8:

2.

31. The battery cell according to claim 20, characterized in that: The lithium-containing transition metal oxide in the positive electrode film layer includes nickel element. Based on the total molar number of transition metals in the lithium-containing transition metal oxide in the positive electrode film layer, the molar proportion of nickel element in the lithium-containing transition metal oxide in the positive electrode film layer is 80%-96%.

32. The battery cell according to claim 31, characterized in that: The molar proportion of nickel element in the lithium-containing transition metal oxide in the positive electrode film layer is 90%-96%.

33. The battery cell according to claim 20, characterized in that: The lithium-containing transition metal oxide in the first positive electrode film layer and the second positive electrode film layer independently comprises a component Li represented by the following general formula: a1 Ni x1 Co y1 M1 z1 M2 w1 O 2-b1 , wherein M1 includes one or more of Mn and Al, M2 includes one or more of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K, 0.8≤a1≤1.2, 0≤x1≤1, 0≤y1≤1, 0≤z1≤1, 0≤w1≤0.1, and -0.1≤b1≤0.

1.

34. 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 5%-50%.

35. 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 20%-40%.

36. The battery cell according to claim 1, characterized in that The single-side thickness of the positive electrode film layer is 25-60 μm.

37. The battery cell according to claim 1, characterized in that The single-side thickness of the positive electrode film layer is 30-50 μm.

38. 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 10-30 N / m.

39. 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 15-25 N / m.

40. 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 with leaking current collectors accounts for 0.1%-2.5%.

41. 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 with leaking current collectors accounts for 0.1%-0.8%.

42. 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 with burrs accounts for 0-2.1%.

43. 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 with burrs accounts for 0-0.05%.

44. The battery cell according to claim 1, characterized in that The charging capacity of the positive electrode plate is 232-238.5 mAh / g.

45. The battery cell according to any one of claims 1 to 44, characterized in that: At -25°C, the time required to discharge the battery cell from 5% SOC to 0% SOC at a discharge rate of 5C is 41-65s.

46. ​​A battery device, characterized in that: Comprising the battery cell according to any one of claims 1-45.

47. An electrical device, characterized in that: The electrical device comprises a battery device as claimed in claim 46, wherein the battery device is used to provide electrical energy.

48. An energy storage device, characterized in that: The energy storage device comprises a battery device as claimed in claim 46, wherein the battery device is used to store electrical energy.

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