Battery cell, battery device and electric device

Abstract

The invention provides a battery monomer, a battery device and a power utilization device, the battery monomer comprises a positive pole piece, the positive pole piece comprises a positive pole current collector, a positive pole film layer arranged on at least one side of the positive pole current collector, and a bottom coating layer arranged between the positive pole current collector and the positive pole film layer on at least one side; the positive electrode film layer comprises a positive electrode active material and a positive electrode film layer conductive agent, and DV90 of particles in the positive electrode film layer is 16-25 [mu] m; the DV90 of the particles in the bottom coating layer is 3-8 [mu] m; and the positive electrode film layer conductive agent comprises a carbon nanotube conductive agent.

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 and an electrical device. Background Art

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

[0003] With the popularization of single-cell applications, the market has put forward higher requirements for their energy density and safety. It is difficult to achieve simultaneous improvement of the above performances in the existing technology, which has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0004] In view of the above problems, the present application provides a battery cell, a battery device and an electrical device, which are described below respectively.

[0005] The first aspect of the present application provides a battery cell, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector, a positive electrode film layer disposed on at least one side of the positive electrode current collector, and a primer layer disposed between the positive electrode current collector and at least one side of the positive electrode film layer; the positive electrode film layer comprises a positive electrode active material and a positive electrode film layer conductive agent, and the D V90 16μm-25μm; D of the particles in the primer layer V90 The thickness of the positive electrode film layer is 3 μm-8 μm; the positive electrode film layer conductive agent includes a carbon nanotube conductive agent.

[0006] In order to improve the compaction density of the electrode, it is necessary to increase the proportion of large particles in the electrode film layer to achieve a dense stacking of the film layer through the grading theory. V90 The compaction density of the pole piece can be increased within the above range, thereby achieving an increase in the energy density of the battery cell. However, the generation of burrs during the cutting process of the high compaction density pole piece is closely related to the large particles in the pole piece film layer. During the slicing process, the cutter squeezes the large particles, which will cause the large particles to squeeze the current collector, causing the current collector to be squeezed and deformed and fractured instead of cut off, thereby generating burrs and affecting the safety performance of the battery.

[0007] In the present application, a small D V90 The base coating forms a transition buffer layer between the positive electrode film layer and the current collector, which can evenly disperse the external mechanical stress applied by the blade during the cutting process, or the internal stress generated by expansion / contraction during the cycle process, reducing the probability of large particles in the positive electrode film layer directly contacting the positive electrode current collector to form stress concentration, resulting in damage and burrs on the positive electrode current collector, thereby improving the safety of the battery.

[0008] Studies have shown that by providing a primer layer on at least one side of the positive electrode current collector surface, the D V90 3 μm-8 μm is conducive to improving the problem of burrs on the positive current collector during slicing. However, the undercoat layer is mainly composed of small particles, and its ultimate compaction density is much smaller than the compaction density of the positive electrode film layer. Therefore, during the compaction process of the positive electrode film layer, the undercoat layer is prone to overpressure, which significantly reduces the porosity in the film layer, increases the rigid contact between the particles, and then leads to a decrease in the overall flexibility of the pole piece and an increase in brittleness, which makes the positive pole piece easy to break during deformation.

[0009] Carbon nanotube conductive agent is used in the positive electrode film layer in the embodiment of the present application. On the one hand, thanks to the high aspect ratio of carbon nanotubes, a large number of active material particles can be connected in series inside the positive electrode film layer, and a tight connection can be formed across the interface between the positive electrode film layer and the base coating layer, thereby increasing the adhesion between the positive electrode film layer and the base coating layer, improving the flexibility of the electrode piece, and reducing the probability of brittle fracture of the electrode piece; on the other hand, its one-dimensional nanostructure provides high specific strength and specific modulus, forming a three-dimensional network structure in the positive electrode film layer, and effectively dissipating external stress through the fiber-matrix interface effect and the bridging effect, reducing the conduction of stress to the base coating layer and the current collector, which can effectively improve the fracture toughness of the material, reduce the rupture of the positive electrode piece caused by volume expansion or contraction, and comprehensively improve the brittleness problem of the positive electrode piece.

[0010] In any embodiment, based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent is 0.3%-0.8%, and can be optionally 0.4%-0.7%. Based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent is within the above range, which reduces the probability of agglomeration of the carbon nanotube conductive agent due to the high specific surface area during the preparation of the positive electrode film layer slurry, maximizes the internal bonding force and stress conduction of the positive electrode plate, optimizes the brittleness, and reduces the probability of powder loss and loose particles falling off during repeated charge and discharge expansion and contraction cycles, and the probability of the falling particles piercing the diaphragm and causing internal short circuits, thereby improving the cycle safety.

[0011] In any embodiment, the positive electrode film layer also includes a binder, and based on the total mass of the positive electrode film layer, the mass proportion of the binder is 0.6%-1.5%, and can be optionally 0.7%-1.3%. The amount of binder used is positively correlated with the internal bonding force of the positive electrode film layer. If the amount of binder is too small, the internal bonding force of the positive electrode film layer is low; if the amount of binder is too high, the resistance of the film layer will be deteriorated and the proportion of active substances will be reduced. The mass proportion of the binder within the above range can maximize the internal bonding force, strengthen the bonding between the particles inside the positive electrode film layer, facilitate stress conduction and reduce crack propagation, reduce the brittleness of the battery, balance the internal resistance of the film layer, reduce ohmic polarization, and improve the energy density and cycle performance of the battery.

[0012] In any embodiment, the D of the particles in the base coating is V90 The particle size of the base coating is 4 μm to 7 μm. V90 Within the above range, the squeezing of the collector by large particles in the positive electrode film during the slicing process can be further effectively buffered, thereby reducing the probability of burrs being generated during the electrode sheet cutting process.

[0013] In any embodiment, the positive electrode active material includes a lithium-containing transition metal oxide, and the molar ratio of nickel in the lithium-containing transition metal oxide is 80%-95% based on the total molar number of transition metals in the lithium-containing transition metal oxide. When the molar ratio of nickel in the lithium-containing transition metal oxide is 80%-95%, since nickel has a high electrochemical activity, the increase in nickel content helps the battery have the advantages of high energy density and high power performance.

[0014] In any embodiment, the positive electrode active material includes a component having the following general formula: Li a Ni x Co y M1 z M2 w O 2-b, where M1 includes one or more of Mn and Al, and M2 includes one or more of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K; 0.8 ≤ a ≤ 1.2, 0.8 ≤ x ≤ 1, 0 < y ≤ 0.2, 0 < z ≤ 0.2, 0 ≤ w ≤ 0.1, -0.1 ≤ b ≤ 0.1. The ionic radii of cobalt and nickel elements are similar, and their electron distributions are similar. The local phase transition of the NiO6 octahedral structure is inhibited by cobalt elements, reducing the non-stoichiometry of LiNiO2 and improving the stability of the layered structure during cycling. M1 does not participate in redox reactions during charge and discharge, so there is no structural change caused by the Jahn-Teller effect, which can thus play a role in stabilizing the layered structure. Selecting appropriate modifying element M2 can further improve the lattice change rate of the cathode active material during lithium deintercalation and intercalation, reduce the oxygen activity on the particle surface, improve the structural stability of the material, and further improve the specific capacity utilization level of the material during cycling, and further improve the cycle life of the lithium-ion secondary battery.

[0015] In any embodiment, the D of the particles in the cathode film layer V50 is 5 μm - 12 μm, (D V90 - D V10 ) / D V50 is 0.5 - 3. The D of the particles in the cathode film layer v50 , (D v90 - D v10 ) / D v50 within the above range enables a reasonable particle size distribution to be formed between smaller particles and larger particles, improving the tap density of the entire cathode film layer and the energy density of the battery cell, while forming a complete pore structure in the cathode film layer, which is beneficial for accommodating carbon nanotubes and binders, forming good connections between particles, enhancing the adhesion force inside the electrode sheet. During cycling, the internal stress of the cathode active material particles is effectively conducted, and the pore structure provides a certain deformation space, reducing the possibility of brittle fracture of the electrode sheet and improving the cycle life of the battery.

[0016] In any embodiment, the cathode active material includes single crystal particles and polycrystalline particles, and the mass ratio of the single crystal particles to the polycrystalline particles is 4:6 - 2:8. Controlling the mass ratio of polycrystalline particles to single crystal particles to meet the above range enables a reasonable particle size distribution to be formed between smaller single crystal particles and larger polycrystalline particles, which is beneficial for improving the tap density of the electrode sheet and enabling the battery to have excellent energy density.

[0017] In any embodiment, the carbon nanotube conductive agent includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes. Single-walled and few-walled carbon nanotubes have extremely high electronic conductivity and can efficiently transfer electrons. A very small amount of addition can effectively reduce the electron transfer impedance inside the battery, increase the load of active materials in the pole piece and the energy density of the battery. Multi-walled carbon nanotubes have multiple carbon layers, which provide stronger mechanical strength and rigidity in structure, can provide stronger support during the charge and discharge process, reduce the impact of electrode expansion and contraction, reduce the brittle fracture of the electrode, and can increase the service life of the battery.

[0018] In any embodiment, the positive electrode film layer conductive agent also includes a spherical conductive agent, and the spherical conductive agent includes one or more of Super-P, acetylene black, and Ketjen black. Due to the one-dimensional structure of the carbon nanotubes, an electron transmission channel can be formed, and a connection can be formed across the layer structure. The spherical conductive carbon particles contact each other to form a regional network with multiple contact points. When carbon nanotubes and spherical conductive carbon are combined, the structures of the two are complementary, and their respective advantages can be brought into play to form a more efficient electron conduction network and improve the adhesion inside the pole piece, further reducing the possibility of brittle fracture.

[0019] In any embodiment, the binder includes at least one of an aqueous binder, a bio-binder, a polyimide binder, and a polyurethane binder, and may be polyvinylidene fluoride. Polyvinylidene fluoride has strong chemical resistance and is not easily affected by electrolytes and other chemicals. It can also maintain good stability at higher temperatures and adapt to the operation of the battery in different temperature environments.

[0020] In any embodiment, the primer layer comprises polyanionic particles comprising a component having 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 0.9≤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.

[0021] In any embodiment, the polyanion particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate and modified materials thereof.

[0022] Polyanion active materials are generally olivine structures, which have good thermodynamic thermal stability compared to lithium-containing transition metal oxides, and can reduce high-temperature oxygen release. Using them as a base coat can improve the burr phenomenon while also improving the safety performance and service life of the battery cell. Polyanion active materials have a lower hardness and are more likely to deform or crush under external forces; in addition, lower hardness may cause particles to rearrange more easily during rolling rather than producing a significant squeezing effect on the current collector. Therefore, using polyanions as a base coat further reduces the probability of burrs.

[0023] In any embodiment, the polyanion particles include one or more of lithium manganese iron phosphate and modified materials thereof.

[0024] Studies have shown that the voltage platform of conventional lithium iron phosphate materials is too low (~3.2V) compared to lithium-containing transition metal oxides, which lowers the voltage platform of the battery cell when the battery is working, making it difficult to fully utilize the gram capacity of lithium iron phosphate. Introducing the Mn element into lithium iron phosphate can effectively increase the voltage platform of lithium iron phosphate (~3.7V), adapting it to the voltage window of lithium-containing transition metal oxides in the positive electrode film layer, which is conducive to the utilization of the material's gram capacity, allowing the bottom coating to reduce the probability of burrs while reducing the negative impact on the battery's energy density.

[0025] In any embodiment, the bottom coating layer includes a bottom coating layer conductive agent, and the bottom coating layer conductive agent includes one or more of conductive carbon black and carbon nanotubes. By adding a conductive agent to the bottom coating layer, it is beneficial to improve the electronic conductivity of the bottom coating layer, and also improve the contact and adhesion between the particles in the coating layer, which is beneficial to improving the cycle life of the battery, improving the power performance and reducing the internal resistance.

[0026] In any embodiment, the thickness of the positive current collector is 7μm-15μm. The positive current collector does not contribute to the capacity of the battery, and its thinning is conducive to making room for the positive active material and improving the energy density of the battery cell. However, the thinning of the positive current collector reduces its ability to withstand large particle extrusion during the slitting process, and the burr phenomenon is more serious. The thickness of the positive current collector within the above range is conducive to improving the yield rate in the pole piece cutting process while maintaining the high energy density of the battery cell, meeting the performance and efficiency requirements.

[0027] In any embodiment, the thickness of the primer layer on one side is 5μm-25μm. The thickness of the primer layer on one side within the above range is conducive to reducing the probability of burrs on the pole piece, and at the same time can reduce the sacrifice of battery capacity and energy density due to excessive thickness of the primer layer, and meet the battery's requirements for safety and energy density. And because the thickness of the primer layer is small, it is at the same order of magnitude as the length of the carbon nanotubes. After cold pressing, the carbon nanotube structure can penetrate into most areas of the primer layer, so that connections are formed between the layers and inside the layered structure, improving the internal bonding force of the pole piece, improving the brittleness of the pole piece, and thus improving the high safety of the battery.

[0028] In any embodiment, the thickness of the positive electrode film layer on one side is 30 μm-50 μm. The thinning of the positive electrode film layer is conducive to reducing the diffusion path length of lithium ions and improving the dynamic performance of the battery cell. However, the thinner the thickness, the greater the probability of burrs piercing the positive electrode film layer, increasing safety hazards. The battery cell in the embodiment of the present application can optimize the dynamic performance of the battery cell while reducing the risk of burrs and improving the safety performance of the battery.

[0029] In any embodiment, the compaction density of the positive electrode film layer in the full discharge state is 3.40 g / cm 3 -3.60g / cm 3 The compaction density of the positive electrode film layer within the above range is conducive to maintaining the high energy density of the battery cell while improving the yield rate in the electrode sheet cutting process, thereby meeting the performance and efficiency requirements.

[0030] A second aspect of the present application provides a battery device, comprising the battery cell of the first aspect of the present application.

[0031] A third aspect of the present application provides an electrical device, comprising at least one of the battery cell of the first aspect of the present application and the battery device of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] 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.

[0033] Figure 1 This is an electron microscope morphology image of a polished cross section of a positive electrode sheet along the thickness direction in one embodiment of the present application; Figure 2 This is an electron microscope morphology image of a polished cross section of a positive electrode sheet along the thickness direction in the prior art; Figure 3 is a schematic diagram of a battery cell according to an embodiment of the present application; Figure 4 yes Figure 3 An exploded view of a battery cell according to an embodiment of the present application is shown; Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 6 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown; Figure 8 Schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0034] Description of reference numerals: 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly; 62 positive electrode plate, 621 positive electrode current collector; 622 positive electrode film layer; 623 bottom coating layer. DETAILED DESCRIPTION

[0035] 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.

[0036] "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.

[0037] 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.

[0038] 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.

[0039] Unless otherwise specified, all steps of the present application may 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 also 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.

[0040] In the present application, the terms "plurality" and "multiple" refer to two or more.

[0041] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0042] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of each parameter is 25°C.

[0043] 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.

[0044] A battery cell is the smallest unit of a battery, which can independently realize the functions of charging and discharging. The battery cell can be cylindrical, rectangular or in other shapes, etc., which is not limited in the embodiments of the present application. Figure 3 The battery cell 5 is a rectangular parallelepiped structure as an example.

[0045] A battery cell includes an electrode assembly and an electrolyte.

[0046] 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).

[0047] In some embodiments, Figure 4 As shown, the outer package may include a shell 51 and a top cover assembly 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 top cover assembly 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.

[0048] The electrode assembly usually includes a positive electrode plate and a negative electrode plate. The negative electrode plate is an electrode that absorbs or lithiates lithium ions during charging and releases or delithiates lithium during discharging. The positive electrode plate is an electrode that releases or delithiates lithium ions during charging and absorbs or lithiates lithium during discharging.

[0049] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed connection through a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a box and battery cells, and the battery cells or battery modules are accommodated in the box. In some embodiments, the box may serve as part of the chassis structure of the vehicle. For example, part of the box may become at least a part of the floor of the vehicle, or part of the box may become at least a part of the crossbeam and longitudinal beam of the vehicle.

[0050] In some embodiments, the battery may be an energy storage device, which includes an energy storage container, an energy storage cabinet, and the like.

[0051] 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 5 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 5 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.

[0052] 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.

[0053] 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.

[0054] Figure 6 and Figure 7 is a schematic diagram of a battery pack 1 as an example. Figure 6 and Figure 7 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.

[0055] In recent years, the market demand for high energy density batteries has become increasingly strong. In order to obtain high compaction density pole pieces and high energy density batteries, the industry's common method is to increase the particle size and proportion of large particles to improve grading, form a dense stack, and increase the compaction density of the pole piece to increase the load of active materials per unit volume. When the positive pole piece is cut, the particles are squeezed against the positive current collector, and large particles are difficult to disperse the pressure. Stress concentration is prone to occur at the contact point with the positive current collector, causing the current collector to be squeezed, deformed and fractured instead of cut off, resulting in burrs, such as Figure 2 As shown. And with the growing demand for fast charging (4C and above) performance, the thinner the electrode film is, the shorter the distance that lithium ions diffuse in the film is, and the faster the diffusion speed is. Therefore, the thickness of the film is also reduced, resulting in the film being unable to cover the burrs, so that the burrs are exposed and pierce the diaphragm, forming an internal short circuit. Therefore, how to avoid burrs and improve battery safety while maintaining energy density is a technical problem that needs to be solved in this field.

[0056] The first aspect of the present application provides a battery cell, wherein the battery cell comprises a positive electrode sheet, such as Figure 1 As shown, the positive electrode sheet 62 includes a positive electrode current collector 621, a positive electrode film layer 622 disposed on at least one side of the positive electrode current collector 621, and an undercoat layer 623 disposed between the positive electrode current collector 621 and at least one side of the positive electrode film layer 622; the positive electrode film layer includes a positive electrode active material and a positive electrode film layer conductive agent, and the D V90 16μm-25μm; D of the particles in the primer layer V90 The thickness of the positive electrode film layer is 3 μm-8 μm; the positive electrode film layer conductive agent includes a carbon nanotube conductive agent.

[0057] In order to improve the compaction density of the electrode, it is necessary to increase the proportion of large particles in the electrode film layer to achieve a dense stacking of the film layer through the grading theory. V90 The compaction density of the pole piece can be increased within the above range, thereby achieving an increase in the energy density of the battery cell. However, the generation of burrs during the cutting process of the high compaction density pole piece is closely related to the large particles in the pole piece film layer. During the slicing process, the cutter squeezes the large particles, which will cause the large particles to squeeze the current collector, causing the current collector to be squeezed and deformed and fractured instead of cut off, thereby generating burrs and affecting the safety performance of the battery.

[0058] In the present application, a small D V90The base coating forms a transition buffer layer between the positive electrode film layer and the current collector, which can evenly disperse the external mechanical stress applied by the blade during the cutting process, or the internal stress generated by expansion / contraction during the cycle process, reducing the probability of large particles in the positive electrode film layer directly contacting the positive electrode current collector to form stress concentration, resulting in damage and burrs on the positive electrode current collector, thereby improving the safety of the battery.

[0059] Studies have shown that by providing a primer layer on at least one side of the positive electrode current collector surface, the D V90 3 μm-8 μm is conducive to improving the problem of burrs on the positive current collector during slicing. However, the undercoat layer is mainly composed of small particles, and its ultimate compaction density is much smaller than the compaction density of the positive electrode film layer. Therefore, during the compaction process of the positive electrode film layer, the undercoat layer is prone to overpressure, which significantly reduces the porosity in the film layer, increases the rigid contact between the particles, and then leads to a decrease in the overall flexibility of the pole piece and an increase in brittleness, which makes the positive pole piece easy to break during deformation.

[0060] Carbon nanotube conductive agent is used in the positive electrode film layer in the embodiment of the present application. On the one hand, thanks to the high aspect ratio of carbon nanotubes, a large number of active material particles can be connected in series inside the positive electrode film layer, and a tight connection can be formed across the interface between the positive electrode film layer and the base coating layer, thereby increasing the adhesion between the positive electrode film layer and the base coating layer, improving the flexibility of the electrode piece, and reducing the probability of brittle fracture of the electrode piece; on the other hand, its one-dimensional nanostructure provides high specific strength and specific modulus, forming a three-dimensional network structure in the positive electrode film layer, and effectively dissipating external stress through the fiber-matrix interface effect and the bridging effect, reducing the conduction of stress to the base coating layer and the current collector, which can effectively improve the fracture toughness of the material, reduce the rupture of the positive electrode piece caused by volume expansion or contraction, and comprehensively improve the brittleness problem of the positive electrode piece.

[0061] In this application, the term "particle" refers to particles with identifiable complete boundaries in the field of view of the positive electrode film layer under a certain magnification, such as 10,000 times. Defects and scratches may exist inside the particles, but complete boundaries sufficient to separate the particles cannot be identified inside the particles.

[0062] In this application, the term "D V90" has a well-known meaning in the art and can be tested by methods known in the art. As an example, the method is as follows: take 2g of sample, add 200ml of NMP solution and 5g of sodium dodecyl sulfate SDS, and disperse under ultrasonic stirring at 60°C for 30min, 60min, 90min..., take solutions with different dispersion times respectively, use a laser particle size analyzer (for example, Malvern 2000 (MasterSizer 2000) laser particle size analyzer), and measure the sample with reference to GB / T 19077-2016 / ISO 13320:2009 standard. When the particle size distribution fluctuation is greater than 5%, continue to increase the ultrasonic dispersion time; when the particle size distribution fluctuation of the solution measured at the last two dispersion times is ≤5%, it means that the dispersion is complete and the test result is accurate. The result can be output to obtain a particle size distribution diagram based on volume distribution. "D V10 ”, “D V50 ” and “D V90 " respectively correspond to the particle sizes when the percentage of particle size distribution reaches 10%, 50%, and 90%.

[0063] In some embodiments, the D of the particles in the positive electrode film layer is V90 It is 16μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, 20μm, 20.5μm, 21μm, 21.5μm, 22μm, 22.5μm, 23μm, 23.5μm, 24μm, 24.5μm, 25μm or a numerical range between any two of the above.

[0064] In some embodiments, the D of the particles in the base coating is V90 The thickness may be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm or a numerical range between any two of the above.

[0065] In this application, the term "burr" refers to a metal protrusion or protrusion extending outward from the current collector in accordance with the IEEE1725 battery cell safety performance review and testing standard; the extension direction can be in any direction, such as the thickness direction or the pole piece plane direction, and the causes of the burr include but are not limited to cutting, tearing, etc.

[0066] In some embodiments, the positive electrode film layer conductive agent includes a carbon nanotube conductive agent.

[0067] In this application, the term "carbon nanotube" refers to carbon atoms in the form of sp 2A nanomaterial with several to dozens of coaxial hollow tubes formed by the curling of graphene sheets formed by hybrid bonding. The diameter is usually in the range of several to dozens of nanometers, and the length can range from microns to centimeters, showing a high aspect ratio. According to the number of layers of graphene sheets, they can be divided into: single-walled carbon nanotubes (SWCNTs), few-walled carbon nanotubes (FWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0068] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent is 0.3%-0.8%, and can be optionally 0.4%-0.7%.

[0069] In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent can be selected as 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or a numerical range between any two of the above.

[0070] Based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent is within the above range, which reduces the probability of agglomeration of the carbon nanotube conductive agent due to the high specific surface area during the preparation of the positive electrode film layer slurry, maximizes the internal bonding force and stress conduction of the positive electrode plate, optimizes the brittleness, and reduces the probability of powder loss and loose particles falling off during repeated charge and discharge expansion and contraction cycles, and the probability of the falling particles piercing the diaphragm and causing internal short circuits, thereby improving the cycle safety.

[0071] In some embodiments, based on the total mass of the positive electrode film layer, the mass proportion of the binder is 0.6%-1.5%, and can be optionally 0.7%-1.3%.

[0072] In some embodiments, the positive electrode film layer also includes a binder. Based on the total mass of the positive electrode film layer, the mass proportion of the binder can be selected to be 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5% or a numerical range between any two of the above.

[0073] The amount of binder used is positively correlated with the internal bonding force of the positive electrode film. If the amount of binder used is too small, the internal bonding force of the positive electrode film is low; if the amount of binder used is too high, the film resistance will deteriorate and the proportion of active substances will be reduced. The mass proportion of the binder within the above range can maximize the internal bonding force, strengthen the bonding between particles inside the positive electrode film, facilitate stress conduction and reduce crack propagation, reduce the brittleness of the battery, balance the internal resistance of the film, reduce ohmic polarization, and improve the energy density and cycle performance of the battery.

[0074] In some embodiments, the D of the particles in the base coating is V90 4μm-7μm.

[0075] D of particles in the base coating V90 Within the above range, the squeezing of the collector by large particles in the positive electrode film during slicing can be further effectively buffered, thereby reducing the probability of burrs being generated during the electrode sheet cutting process.

[0076] In some embodiments, the positive electrode active material includes a lithium-containing transition metal oxide, and the molar proportion of nickel element in the lithium-containing transition metal oxide is 80%-95% based on the total molar number of transition metals in the lithium-containing transition metal oxide.

[0077] Lithium-containing transition metal oxides are an important type of positive electrode active material for lithium-ion batteries. When the molar proportion of nickel in the lithium-containing transition metal oxides is 80%-95%, due to the high electrochemical activity of nickel, the increase in nickel content helps to make the battery have the advantages of high energy density and high power performance.

[0078] In some embodiments, the positive electrode active material has the following chemical formula: Li a Ni x Co y M1 z M2 w O 2-b , wherein M1 includes one or more of Mn and Al, and M2 includes one or more of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K; 0.8≤a≤1.2, 0.8≤x≤1, 0 <y≤0.2,0<z≤0.2,0≤w≤0.1,-0.1≤b≤0.1。

[0079] In some embodiments, a can be selected as 0.80, 0.82, 0.84, 0.86, 0.88, 0.90, 0.92, 0.94, 0.96, 0.98, 1.00, 1.02, 1.04, 1.06, 1.08, 1.10, 1.12, 1.14, 1.16, 1.18, 1.20 or a range of values ​​between any two of the above.

[0080] In some embodiments, x can be selected as 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 or a range of values ​​therebetween.

[0081] In some embodiments, y can be selected as 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 or a range of values ​​between any two of the above.

[0082] In some embodiments, z can be selected as 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 or a range of values ​​between any two of the above.

[0083] In some embodiments, w can be selected as 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or a numerical range therebetween.

[0084] In some embodiments, b can be selected as -0.10, -0.09, -0.08, -0.07, -0.06, -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10 or a numerical range between any two of the above.

[0085] Li a Ni x Co y M1 z M2 w O 2-bThe ionic radius of cobalt and nickel are similar, and the electron distribution is similar. The local phase change of the NiO6 octahedral structure is suppressed by cobalt, which reduces the non-stoichiometric ratio of LiNiO2 and improves the stability of the layered structure during the cycle. M1 does not participate in the redox reaction during the charge and discharge process, so there is no structural change caused by the Chiang-Taylor effect, which can play a role in stabilizing the layered structure. Selecting an appropriate modifying element M2 can further improve the lattice change rate of the positive electrode active material during the lithium insertion and extraction process, reduce the oxygen activity on the particle surface, and improve the structural stability of the material, thereby improving the material's gram capacity during the cycle, and further improving the cycle life of lithium-ion secondary batteries.

[0086] In some embodiments, the D of the particles in the positive electrode film layer is V50 5μm-12μm, (D V90 -D V10 ) / D V50 It is 0.5-3.

[0087] In some embodiments, the D of the particles in the positive electrode film layer is V50 Optional 5μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6μm, 6.1μm, 6.2μm, 6.3μm, 6.4μm, 6.5μm, 6.6μm, 6.7μm, 6.8μm, 6.9μm, 7μm, 7.1μm, 7.2μm, 7.3μm, 7.4μm, 7.5μm, 7.6μm, 7.7μm, 7.8μm, 7.9μm, 8μm, 8.1μm, 8.2μm, 8.3μm, 8.4μm, 8.5μm, 8.6μm, 8.7μm, 8.8 1 0.6μm, 10.7μm, 10.8μm, 10.9μm, 11μm, 11.1μm, 11.2μm, 11.3μm, 11.4μm, 11.5μm, 11.6μm, 11.7μm, 11.8μm, 11.9μm, 12μm or a numerical range between any two of the above.

[0088] In some embodiments, the particles in the positive electrode film layer (D V90 -D V10 ) / D V50The options include 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 or a numerical range between any two of the above.

[0089] In this application, the term "D V50 , D V10 " has a well-known meaning in the art and can be tested by methods known in the art. Please refer to the above-mentioned particle size distribution test method.

[0090] D of particles in the positive electrode film v50 , (D v90 -D v10 ) / D v50 Within the above range, a reasonable particle grading is formed between smaller particles and larger particles, which improves the compaction density of the entire positive electrode film layer and the energy density of the battery cell. At the same time, the positive electrode film layer forms a complete pore structure, which is conducive to accommodating carbon nanotubes and binders, forming good connections between particles, and enhancing the bonding force inside the electrode sheet. During the cycle, the internal stress of the positive electrode active material particles is effectively conducted, and the pore structure provides a certain deformation space, which reduces the possibility of brittle fracture of the electrode sheet and improves the cycle life of the battery.

[0091] In some embodiments, the positive electrode active material includes single crystal particles and polycrystalline particles, and the mass ratio of the single crystal particles to the polycrystalline particles is 4:6-2:8.

[0092] In some embodiments, the positive electrode active material includes single crystal particles and polycrystalline particles, and the mass ratio of the single crystal particles to the polycrystalline particles can be selected as 4:6, 3.9:6.1, 3.8:6.2, 3.7:6.3, 3.6:6.4, 3.5:6.5, 3.4:6.6, 3.3:6.7, 3.2:6.8, 3.1:6.9, 3:7, 2.9:7.1, 2.8:7.2, 2.7:7.3, 2.6:7.4, 2.5:7.5, 2.4:7.6, 2.3:7.7, 2.2:7.8, 2.1:7.9, 2:8 or a numerical range between any two of the above.

[0093] In this application, the term "single crystal" refers to a crystal whose internal structure basically conforms to a lattice structure. A single crystal contains no or a small amount of grain boundaries within a macroscopic scale, and the crystal orientation is basically consistent everywhere inside.

[0094] In this application, the term "polycrystalline" refers to a crystal composed of many single crystal particles with different orientations. The entire structure is not penetrated by the same lattice. The hard agglomeration of single crystal particles caused by chemical bonding makes the polycrystalline particles have more grain boundaries.

[0095] In the present application, the mass ratio of polycrystalline particles and single crystal particles can be determined by the following method: take a prepared positive electrode plate, or a positive electrode plate disassembled from a battery, and perform a CP-SEM test. Randomly select a number of points for shooting, and the number of points is ≥10, which can be 10, 20, 50, 100, etc. The area ratio of the polycrystalline particles and the single crystal particles in the captured image to the size of the positive electrode film layer is calculated, and the average value is obtained. The area ratio between polycrystalline particles and single crystal particles can be equivalent to the mass ratio of polycrystalline particles to single crystal particles.

[0096] The mass ratio of polycrystalline particles and single crystal particles is controlled to meet the above range, and a reasonable particle grading is formed between the smaller single crystal particles and the larger polycrystalline particles, which is beneficial to improving the compaction density of the electrode and making the battery have excellent energy density.

[0097] In some embodiments, the D V50 1μm-5μm; and / or D V50 5μm-11μm.

[0098] In some embodiments, the D V50 The optional value is 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm, 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm, 4.5μm, 4.6μm, 4.7μm, 4.8μm, 4.9μm, 5μm or a numerical range between any two of the above.

[0099] In some embodiments, the D V50Optional 5μm, 5.1μm, 5.2μm, 5.3μm, 5.4μm, 5.5μm, 5.6μm, 5.7μm, 5.8μm, 5.9μm, 6μm, 6.1μm, 6.2μm, 6.3μm, 6.4μm, 6.5μm, 6 .6μm, 6.7μm, 6.8μm, 6.9μm, 7μm, 7.1μm, 7.2μm, 7.3μm, 7.4μm, 7.5μm, 7.6μm, 7.7μm, 7.8μm, 7.9μm, 8μm, 8.1μm, 8.2μm , 8.3μm, 8.4μm, 8.5μm, 8.6μm, 8.7μm, 8.8μm, 8.9μm, 9μm, 9.1μm, 9.2μm, 9.3μm, 9.4μm, 9.5μm, 9.6μm, 9.7μm, 9.8μm, 9.9μm, 10μm, 10μm, 10μm, 10.1μm, 10.2μm, 10.3μm, 10.4μm, 10.5μm, 10.6μm, 10.7μm, 10.8μm, 10.9μm, 11μm or a numerical range between any two of the above.

[0100] The D of the single crystal particle and the polycrystalline particle V50 Within the above range, the single crystal particles can fill the pores formed by the accumulation of polycrystalline particles, making more effective use of the space, thereby increasing the compaction density of the entire positive electrode sheet and the energy density of the battery cell.

[0101] In some embodiments, the carbon nanotube conductive agent in the positive electrode film layer includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0102] Single-walled and few-walled carbon nanotubes have extremely high electronic conductivity and can efficiently transfer electrons. A very small amount of addition can effectively reduce the electron transmission impedance inside the battery, increase the load of active materials in the pole piece and the energy density of the battery. Multi-walled carbon nanotubes have multiple carbon layers, which provide stronger mechanical strength and rigidity in structure. They can provide stronger support during the charge and discharge process, reduce the impact of electrode expansion and contraction, reduce the brittle fracture of the electrode, and increase the service life of the battery.

[0103] In some embodiments, the positive electrode film layer conductive agent further comprises a spherical conductive agent, and the spherical conductive agent comprises one or more of Super-P, acetylene black, and Ketjen black.

[0104] Due to the one-dimensional structure of carbon nanotubes, electron transmission channels can be formed and connections can be formed across layer structures. Spherical conductive carbon particles contact each other to form a regional network with multiple contact points. When carbon nanotubes and spherical conductive carbon are combined, the structures of the two complement each other and can play their respective advantages to form a more efficient electron conduction network and improve the bonding force inside the pole piece, further reducing the possibility of brittle fracture.

[0105] In some embodiments, the adhesive includes at least one of an aqueous adhesive, a biological adhesive, a polyimide adhesive, and a polyurethane adhesive, and may be polyvinylidene fluoride.

[0106] The binder used in this application includes but is not limited to the above-mentioned types of binders, which can bind active materials, conductive agents and other components together in the positive electrode film layer, and have a certain bonding strength, which can meet the requirements of this application. Polyvinylidene fluoride has strong chemical corrosion resistance, is not easily affected by electrolytes and other chemicals, and can maintain good stability at higher temperatures, adapting to the operation of batteries in different temperature environments.

[0107] In some embodiments, the primer layer includes polyanionic particles comprising a component having 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 0.9≤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.

[0108] In some embodiments, x can 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, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, or a range of values ​​therebetween.

[0109] In some embodiments, y can be selected as 0, 0.05, 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, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3 or a range of values ​​between any two of the above.

[0110] In some embodiments, x+y can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3 or a numerical range therebetween.

[0111] In some embodiments, a can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or a range of values ​​therebetween.

[0112] In some embodiments, b can be selected as 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5 or a range of values ​​between any two of the above.

[0113] In some embodiments, a+b can be selected as 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5 or a range of values ​​therebetween.

[0114] In some embodiments, c can be selected as 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5 or a range of values ​​between any two of the above.

[0115] In some embodiments, z can 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 a range of values ​​therebetween.

[0116] When used in this article, "the polyanion particles include components having the following general formula I" is not limited to the substances represented by the molecular general formula, but also includes other substances formed after further appropriate modification on the basis of the molecular general formula, which is not limited here. The use of "general formula" is only for the convenience of description and is not intended to limit this application. It can be understood that new materials or new substances obtained by appropriate modification on the basis of the listed materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for materials, and non-limiting examples include coating modification.

[0117] Polyanion active materials are generally olivine structures, which have good thermodynamic thermal stability compared to lithium-containing transition metal oxides, and can reduce high-temperature oxygen release. Using them as a base coat can improve the burr phenomenon while also improving the safety performance and service life of the battery cell. Polyanion active materials have a lower hardness and are more likely to deform or crush under external forces; in addition, lower hardness may cause particles to rearrange more easily during rolling rather than producing a significant squeezing effect on the current collector. Therefore, using polyanions as a base coat further reduces the probability of burrs.

[0118] In some embodiments, the polyanion particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium fluorovanadium phosphate, lithium manganese iron phosphate, and modified materials thereof.

[0119] In some embodiments, the polyanion particles include one or more of lithium manganese iron phosphate and modified materials thereof.

[0120] Studies have shown that the voltage platform of conventional lithium iron phosphate materials is too low (~3.2V) compared to lithium-containing transition metal oxides, which lowers the voltage platform of the battery cell when the battery is working, making it difficult to fully utilize the gram capacity of lithium iron phosphate. Introducing the Mn element into lithium iron phosphate can effectively increase the voltage platform of lithium iron phosphate (~3.7V), adapting it to the voltage window of lithium-containing transition metal oxides in the positive electrode film layer, which is conducive to the utilization of the material's gram capacity, allowing the bottom coating to reduce the probability of burrs while reducing the negative impact on the battery's energy density.

[0121] In some embodiments, the primer layer includes a primer conductive agent, and the primer conductive agent includes one or more of conductive carbon black and carbon nanotubes.

[0122] By adding a conductive agent to the base coating, the electronic conductivity of the base coating is improved, and the contact and adhesion between the particles in the coating are improved, which is beneficial to increasing the cycle life of the battery, improving power performance and reducing internal resistance.

[0123] In some embodiments, the thickness of the positive electrode current collector is 7 μm-15 μm.

[0124] In some embodiments, the thickness of the positive electrode current collector may be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or a numerical range between any two of the above.

[0125] In the present application, the thickness of the positive electrode current collector can be measured in the following manner: the positive electrode film layer is cut along the thickness direction of the pole piece by an argon ion beam (for example, equipment model: Leica EM TIC 3X CP, working voltage: 6kV, working time: 6h), and after the section is exposed, a scanning electron microscope (as an example, the following can be selected: equipment model: Hitachi SU8230, working voltage: 3kV, beam current: high, probe model: U (LA100), working distance <5mm) is used to observe the section of the positive electrode film layer along the thickness direction of the pole piece. The thickness of the positive electrode current collector is measured based on the scale in the electron microscope image.

[0126] The positive electrode current collector does not contribute to the capacity of the battery, and its thinning is conducive to making room for the positive electrode active material and improving the energy density of the battery cell. However, the thinning of the positive electrode current collector reduces its ability to withstand large particle extrusion during the slitting process, and the burr phenomenon is more serious. The thickness of the positive electrode current collector within the above range is conducive to improving the yield rate during the electrode cutting process while maintaining the high energy density of the battery cell, meeting the performance and efficiency requirements.

[0127] In some embodiments, the thickness of the primer layer on one side is 5 μm-25 μm.

[0128] In some embodiments, the thickness of the primer layer on one side may be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm or a range of values ​​between any two of the above.

[0129] The thickness of the single-sided bottom coating within the above range is conducive to reducing the probability of burrs on the pole piece, and at the same time can reduce the sacrifice of battery capacity and energy density due to excessive thickness of the bottom coating, meeting the battery's requirements for safety and energy density. And because the thickness of the bottom coating is small, it is at the same order of magnitude as the length of the carbon nanotubes. After cold pressing, the carbon nanotube structure can penetrate into most areas of the bottom coating layer, so that connections are formed between the layers and inside the layered structure, improving the internal bonding force of the pole piece, improving the brittleness of the pole piece, and thus improving the high safety of the battery.

[0130] In some embodiments, the thickness of the bottom positive electrode film layer on one side is 30 μm-50 μm.

[0131] In some embodiments, the thickness of the primer layer on one side may be 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, 50 μm or a range of values ​​between any two of the above.

[0132] Reducing the thickness of the positive electrode film layer is beneficial to reducing the diffusion path length of lithium ions and improving the dynamic performance of the battery cell. However, the thinner the thickness, the greater the probability of burrs piercing the positive electrode film layer, increasing safety hazards. The battery cell in the embodiment of the present application can optimize the dynamic performance of the battery cell while reducing the risk of burrs, thereby improving the safety performance of the battery.

[0133] In some embodiments, the cold pressed density of the positive electrode film layer is 3.50 g / cm 3 -3.75g / cm 3 .

[0134] In some embodiments, the cold pressed density of the positive electrode film layer can be 3.50 g / cm 3 、3.51g / cm 3 、3.52g / cm 3 、3.53g / cm 3 、3.54g / cm 3 、3.55g / cm 3 、3.56g / cm 3 、3.57g / cm 3 、3.58g / cm 3 、3.59g / cm 3 、3.6g / cm 3 、3.61g / cm 3 、3.62g / cm 3 、3.63g / cm 3 、3.64g / cm 3 、3.65g / cm 3 、3.66g / cm 3 、3.67g / cm 3 、3.68g / cm 3 、3.69g / cm 3 、3.7g / cm 3 , 3.71g / cm3, 3.72g / cm3, 3.73g / cm3, 3.74g / cm3, 3.75g / cm3 or a numerical range between any two of the above.

[0135] In this application, the compaction density after cold pressing can be tested by methods known in the art. As an example, the positive electrode sheet obtained after cold pressing is cut into small discs with an area of ​​S, and its mass is W1, and the thickness T1 of the positive electrode sheet is measured using a micrometer, and then the positive electrode film layer of the weighed electrode sheet is wiped off, and the mass of the current collector is weighed, recorded as W2, and the thickness T2 of the current collector is measured using a micrometer, then the compaction density of the positive electrode film layer PD = (W1-W2) / [(T1-T2)×S].

[0136] In some embodiments, the compaction density of the positive electrode film layer in a fully charged state is 3.40 g / cm 3 -3.60g / cm 3 .

[0137] In some embodiments, the compaction density of the positive electrode film layer in a fully charged state is 3.40 g / cm 3 、3.41g / cm 3 、3.42g / cm 3 、3.43g / cm 3 、3.44g / cm 3 、3.45g / cm 3 、3.46g / cm 3 、3.47g / cm 3 、3.48g / cm 3 、3.49g / cm 3 、3.50g / cm 3 、3.51g / cm 3 、3.52g / cm 3 、3.53g / cm 3 、3.54g / cm 3 、3.55g / cm 3 、3.56g / cm 3 、3.57g / cm 3 、3.58g / cm 3 、3.59g / cm 3 、3.60g / cm 3 Or a numerical range between any two of the above.

[0138] In this application, the full discharge state means that the battery is placed at 25°C, left to stand for 2 hours, and when the battery temperature remains at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.8V, then left to stand for 30 minutes, and then continued to be discharged at a constant current of 0.04C to 2.8V In the present application, the compaction density of the positive electrode film layer in the full state can be tested by methods known in the art. As an example, the battery is placed in a 25°C oven environment and left to stand for 2 hours. When the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.8V and then left to stand for 15 minutes. It is further discharged at a constant current of 0.04C to 2.8V. The battery is disassembled to obtain the positive electrode plate, and the residual electrolyte is treated with dimethyl carbonate solvent. The plate is dried and cut into small discs with an area of ​​S, and its mass is obtained as W1. The thickness T1 of the positive electrode plate is measured using a micrometer, and then the positive electrode film layer of the weighed plate is wiped off, and the mass of the current collector is weighed, recorded as W2, and the thickness T2 of the current collector is measured using a micrometer. Then the compaction density PD of the positive electrode film layer is PD = (W1-W2) / [(T1-T2)×S].

[0139] The compaction density of the positive electrode film layer within the above range is beneficial to maintaining the high energy density of the battery cell while improving the yield rate in the electrode sheet cutting process, thereby meeting the performance and efficiency requirements.

[0140] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0141] In some embodiments, the primer layer may further include a binder, which may include, for example, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0142] In some embodiments, the positive electrode plate can be prepared in the following manner: the components for preparing the primer layer, such as lithium-containing transition metal phosphate, conductive agent, binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a primer layer slurry; the components such as lithium-containing transition metal oxide, conductive agent, binder are dispersed in a solvent to form a positive electrode film layer slurry; the primer layer slurry is first coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode film layer slurry is then coated on the surface of the primer layer, and after drying, cold pressing and other processes, the positive electrode plate can be obtained.

[0143] [Negative electrode] The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector.

[0144] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0145] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0146] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0147] In some embodiments, the negative electrode film layer may further include a binder, which may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0148] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0149] In some embodiments, the negative electrode film layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0150] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0151] [Electrolytes] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0152] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0153] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0154] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0155] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0156] [Isolation film] In some embodiments, the battery cell further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0157] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0158] [Battery Cell] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0159] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0160] In some embodiments, the volume energy density of the battery cell is 650Wh / L-720Wh / L.

[0161] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape.

[0162] [Battery device] The present application also provides a battery device, which includes the battery cell provided in the present application. In some embodiments, the battery device is one or more of a battery module, a battery pack, and an energy storage device.

[0163] [Electrical devices] In addition, an embodiment of the present application further provides an electric device, which includes at least one of the battery cells, battery modules, or battery packs provided in the embodiments of the present application. The battery cells, battery modules, or battery packs can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0164] As the electrical device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0165] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the power consumption device's requirements for high power and high energy density of battery cells, a battery pack or a battery module can be used.

[0166] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a battery cell may be used as a power source.

[0167] 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.

[0168] Example 1 1) Preparation of positive electrode Preparation of base coating slurry: V90 6μm lithium manganese iron phosphate (LiMn 0.6 Fe 0.4 PO4), carbon nanotube conductive agent, conductive carbon black, and binder PVDF are mixed in a mass ratio of 98:05:0.5:1, and a solvent N-methyl-2-pyrrolidone (NMP) is added, and the mixture is stirred under a vacuum stirrer until the system is uniform to obtain a primer slurry; Preparation of positive electrode film slurry: D V90 25μm, D V50 9μm, D V10 2.5μm polycrystalline lithium-containing transition metal oxide LiNi 0.92 Co 0.04 Mn 0.04 O2,D V90 11μm, D V50 0 is 4.5μm, D V10 1.5μm single crystal lithium-containing transition metal oxide LiNi 0.92 Co 0.04 Mn 0.04 O2 weighs a positive electrode active material mixture at a mass ratio of 7:3 (the mass ratio of polycrystalline: single crystal is = 7:3), the positive electrode active material mixture, carbon nanotube conductive agent, conductive carbon black, and binder PVDF are mixed at a mass ratio of 97.7:0.5:0.5:1.3, and a solvent NMP is added. The mixture is stirred under the action of a vacuum stirrer until the system is uniform, thereby obtaining a positive electrode film slurry; The primer slurry is evenly coated on both sides of the positive electrode current collector and then dried to form a primer layer, wherein the coating weight on one side is 40 mg / 1540.25 mm 2 ; The positive electrode film slurry is evenly coated on the surface of the base coating away from the positive electrode current collector, and the single-sided coating mass is 160mg / 1540.25mm 2 After drying at room temperature, the coating is transferred to an oven for further drying, and then cold pressed to obtain the positive electrode sheet. The single-sided coating mass here does not include the solvent mass, but only the solid content mass in the coating.

[0169] Among them, after cold pressing, the thickness of the bottom coating on one side of the positive electrode sheet is 10 μm, and the volume distribution particle size D of the particles in the bottom coating is V90 6μm; The thickness of the positive electrode film on one side of the positive electrode sheet is 40 μm, and the D V90 22μm, D V50 8μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 3.7 g / cm 3 .

[0170] Pole sheet slitting (one out of two): The positive electrode sheet is slitting on the slitting machine, the slitting speed is 0.5m / s, the slitting knife is made of steel, and the negative pressure of the slitting machine is -10KPa Pole piece cutting: The slit pole pieces are wound and cut, with a winding speed of 0.6m / s, each winding core length of 3m, the cutting knife is made of steel, and the negative pressure in the winding machine is -10KPa.

[0171] 2) Preparation of negative electrode sheet The graphite negative electrode active material, polyvinyl alcohol binder, and SP-Li conductive agent were fully mixed and ball-milled in a deionized water solvent system at a mass ratio of 90:5:5 to obtain a negative electrode slurry. The negative electrode slurry was mixed at a mass ratio of 148 mg / 1540.25 mm 2 The single-sided coating weight of the film was double-sided coated on the surface of the copper foil and vacuum dried overnight at a temperature of 110° C. to obtain a negative electrode sheet.

[0172] 3) Preparation of diaphragm A polyethylene film with a thickness of 13 μm was used as the separator.

[0173] 4) Preparation of electrolyte Lithium hexafluorophosphate (LiPF6) was dissolved in ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1 to form a uniform solution, thereby obtaining an electrolyte with a LiPF6 concentration of 1 mol / L.

[0174] 5) Battery assembly Place them in the order of "diaphragm-negative electrode sheet-diaphragm-positive electrode sheet", fix one end of the positive electrode sheet, negative electrode sheet and two separators to the discharge roller, and fix the other end to the winding shaft after stacking together. Use a motor to rotate the winding shaft, wind up the positive electrode sheet, negative electrode sheet and two separators, and obtain a wound bare cell. Place the bare cell in an outer package, inject the above-mentioned electrolyte and package it to obtain a battery cell.

[0175] The preparation method of Example 2 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, the carbon nanotube conductive agent, the conductive carbon black, and the binder PVDF is adjusted to 97.7:0.8:0.2:1.3, and other parameter conditions remain unchanged.

[0176] The preparation method of Example 3 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, the carbon nanotube conductive agent, the conductive carbon black, and the binder PVDF is adjusted to 97.7:0.7:0.3:1.3, and other parameter conditions remain unchanged.

[0177] The preparation method of Example 4 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, carbon nanotube conductive agent, conductive carbon black, and binder PVDF is adjusted to 97.7:0.4:0.6:1.3, and other parameter conditions remain unchanged.

[0178] The preparation method of Example 5 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, carbon nanotube conductive agent, conductive carbon black, and binder PVDF is adjusted to 97.7:0.3:0.7:1.3, and other parameter conditions remain unchanged.

[0179] The preparation method of Example 6 is basically the same as that of Example 1, except that D is used in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry. V90 19μm, D V50 7μm, D V10 2.2μm polycrystalline lithium-containing transition metal oxide LiNi 0.92 Co 0.04 Mn 0.04 O2 replaces the original polycrystalline lithium-containing transition metal oxide; after cold pressing, the thickness of the positive electrode film on one side of the positive electrode sheet is 40 μm, and the D V90 16μm, D V50 6.2μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 3.67 g / cm 3 , other parameters remain unchanged.

[0180] The preparation method of Example 7 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, D V90 27μm, D V50 10μm, DV10 4μm polycrystalline lithium-containing transition metal oxide LiNi 0.92 Co 0.04 Mn 0.04 O2 replaces the original polycrystalline lithium-containing transition metal oxide; after cold pressing, the thickness of the positive electrode film on one side of the positive electrode sheet is 40 μm, and the D V90 25μm, D V50 8.7 μm, (D V90 -D V10 ) / D V50 The cold pressed density of the positive electrode film is 3.65g / cm 3 , other parameters remain unchanged.

[0181] The preparation method of Example 8 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the undercoat slurry, D V90 The original lithium manganese iron phosphate is replaced by lithium manganese iron phosphate with a thickness of 8 μm; after cold pressing, the thickness of the bottom coating on one side of the positive electrode sheet is 10 μm, and the volume distribution particle size D of the particles in the bottom coating is V90 The thickness of the nanostructured carbon foam was 8 μm, and the other parameters remained unchanged.

[0182] The preparation method of Example 9 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the undercoat slurry, D V90 7μm lithium manganese iron phosphate replaces the original lithium manganese iron phosphate; after cold pressing, the thickness of the bottom coating on one side of the positive electrode sheet is 10μm, and the volume distribution particle size D of the particles in the bottom coating is V90 The other parameters remain unchanged.

[0183] The preparation method of Example 10 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the undercoat slurry, D V90 4μm lithium manganese iron phosphate replaces the original lithium manganese iron phosphate; after cold pressing, the thickness of the bottom coating on one side of the positive electrode sheet is 10μm, and the volume distribution particle size D of the particles in the bottom coating is V90 The thickness of the nanostructured carbon foam was 4 μm, and the other parameters remained unchanged.

[0184] The preparation method of Example 11 is basically the same as that of Example 1, except that D is used in the preparation of the positive electrode sheet and the preparation of the undercoat slurry. V90 3μm lithium manganese iron phosphate replaces the original lithium manganese iron phosphate; after cold pressing, the thickness of the bottom coating on one side of the positive electrode sheet is 10μm, and the volume distribution particle size D of the particles in the bottom coating is V90 The thickness is 3 μm, and other parameters remain unchanged.

[0185] The preparation method of Example 12 is basically the same as that of Example 1, except that, in the preparation of the positive electrode plate and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, carbon nanotube conductive agent, conductive carbon black, and binder PVDF is adjusted to 97.5:0.5:0.5:1.5, and other parameter conditions remain unchanged.

[0186] The preparation method of Example 13 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, carbon nanotube conductive agent, conductive carbon black, and binder PVDF is adjusted to 97.8:0.5:0.5:1.2, and other parameter conditions remain unchanged.

[0187] The preparation method of Example 14 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, the carbon nanotube conductive agent, the conductive carbon black, and the binder PVDF is adjusted to 98.3:0.5:0.5:0.7, and other parameter conditions remain unchanged.

[0188] The preparation method of Example 15 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, the carbon nanotube conductive agent, the conductive carbon black, and the binder PVDF is adjusted to 98.4:0.5:0.5:0.6, and other parameter conditions remain unchanged.

[0189] The preparation method of Example 16 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, the carbon nanotube conductive agent, the conductive carbon black, and the binder PVDF is adjusted to 98.5:0.5:0.5:0.5, and other parameter conditions remain unchanged.

[0190] The preparation method of Example 17 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the undercoat slurry, D V90 6μm lithium iron phosphate (LiFePO4, LFP) replaces the original lithium manganese iron phosphate, and other parameters remain unchanged.

[0191] The preparation method of Example 18 is basically the same as that of Example 1, except that in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry, polycrystalline lithium-containing transition metal oxide LiNi is used. 0.92 Co 0.04 Al 0.04 O2 replaces the original polycrystalline lithium-containing transition metal oxide, and the single crystal lithium-containing transition metal oxide LiNi 0.92 Co 0.04 Al 0.04O2 replaces the original single crystal lithium-containing transition metal oxide, and other parameters remain unchanged.

[0192] The preparation method of Comparative Example 1 is substantially the same as that of Example 1, except that, in the preparation steps of the positive electrode sheet, no primer slurry is prepared and no coating is performed.

[0193] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that D is used in the preparation of the positive electrode sheet and the preparation of the undercoat slurry. V90 The 10μm lithium manganese iron phosphate replaces the original lithium manganese iron phosphate; after cold pressing, the thickness of the bottom coating on one side of the positive electrode sheet is 10μm, and the volume distribution particle size D of the particles in the bottom coating is V90 The cold pressed density of the positive electrode film is 3.68 g / cm 3 Other parameters remain unchanged.

[0194] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that, in the preparation of the positive electrode sheet and the preparation step of the positive electrode film slurry, the mass ratio of the positive electrode active material mixture, the conductive carbon black, and the binder PVDF is adjusted to 97.7:1:1.3, and other parameter conditions remain unchanged.

[0195] The preparation method of Comparative Example 4 is basically the same as that of Example 1, except that D is used in the preparation of the positive electrode sheet and the preparation of the positive electrode film slurry. V90 15μm, D V50 6.4μm, D V10 2.0μm polycrystalline lithium-containing transition metal oxide LiNi 0.92 Co 0.04 Mn 0.04 O2 replaces the original polycrystalline lithium-containing transition metal oxide; after cold pressing, the thickness of the positive electrode film on one side of the positive electrode sheet is 40 μm, and the D V90 14μm, D V50 6μm, (D V90 -D V10 ) / D V50 2; the cold pressed density of the positive electrode film is 3.60g / cm 3 , other parameters remain unchanged.

[0196] Performance Testing 1. CP-SEM characterization method of positive electrode cross section The sample to be characterized was prepared as follows: first, the positive electrode sheet was cut into a sample to be tested with a size of 2 cm × 2 cm, and the sample to be tested was fixed on the sample stage by paraffin. Then, the sample stage was placed in the sample holder and locked, the power supply and vacuum of the argon ion cross-section polisher IB-19500CP were turned on, the argon gas flow rate was set to 0.15 MPa, the control voltage was set to 8 KV, and the polishing time was set to 2 hours, and the sample stage was adjusted to the swing mode to start polishing. After the polishing was completed, the sample to be characterized was obtained.

[0197] Microscopic morphology characterization: The samples were characterized using a scanning electron microscope ZEISS Sigma300. The sample test can refer to JY / T010-1996. In order to ensure the accuracy of the test results, multiple different areas can be randomly selected from the sample to be tested for scanning tests, and the cross-sectional morphology images can be taken at a fixed magnification of 5k times.

[0198] 2. Characterization method of burr test on positive electrode section At 25°C, the positive electrode pieces cut in each embodiment and comparative example were characterized using a CCD instrument (Keyence 600). The size of the test piece was 80 mm × 60 mm, the magnification was 300x, and the light opening was 30%. The burrs were characterized and observed from the cut section of the piece and the size was calibrated. The burrs with a size greater than or equal to 40% of the thickness of the positive electrode piece were included in the statistical range and calibrated as positive electrode pieces with burrs.

[0199] Burr size statistics: 2000 cut pole pieces were observed by CCD, and the frequency K1 of pole pieces with burrs was counted. The burr ratio was calculated to be K1÷2000×100%.

[0200] 3. Pole powder shedding test At 25°C, the cold-pressed positive electrode sheets prepared in each embodiment and comparative example were taken and sheared by a die-cutting and wrap-around integrated machine. The slitting speed was set to 0.5 m / s, the pressure of the slitting machine was -10 Kpa, and the number of shearing knives was 2000. The powder after shearing was collected, and its weight was weighed and recorded as W. The proportion of metal leakage was recorded as W g / 2000 knives.

[0201] 4. Pole piece bonding strength test method At 25°C, take the cold-pressed positive electrode sheets prepared in each embodiment and comparative example, cut them into test specimens with a length of L: 100 mm and a width of W: 20 mm, and set them aside; stick one side of the double-sided tape to the surface of the steel plate, and adhere the electrode to be tested on the other side, and compact it with a roller to make it completely fit with the electrode; bend one end of the collector in the opposite direction, and the bending angle is 180°; use a high-speed rail tensile testing machine for testing, fix one end of the steel plate to the clamp below the tensile testing machine, and fix the bent end of the collector to the upper clamp, adjust the angle of the collector to ensure that the upper and lower ends are in a vertical position, and then stretch the sample at a speed of 50 mm / min until the collector is completely peeled off from the surface of the electrode, record the displacement and force in the process, and record the strength when the force is balanced as the bonding force of the electrode as N1. The bonding strength of the electrode can be calculated using the formula N1 / W.

[0202] 5. Bending resistance At 25°C, the positive electrode sheets cut in each embodiment and comparative example were folded at 180°, rolled back and forth at the fold with a 1.5 kg roller, and then unfolded to observe whether cracks and light transmission occurred at the fold; then, they were folded in the opposite direction at 180°, rolled back and forth at the fold with a 1.5 kg roller, and then unfolded to observe whether cracks and light transmission occurred at the fold, and the above reverse folding steps were repeated, and each folding was recorded as 0.5 times of bending resistance, and the number of folding times that caused cracks and light transmission to occur at the fold was recorded, and at least ten samples were tested, and the average value was taken as the bending resistance number of the positive electrode sheet.

[0203] 6. Battery internal resistance DCR test method At 25°C, the battery cells prepared in each embodiment and comparative example were charged at a constant current of 1 / 3C to a charge cut-off voltage of 4.25V, and then continued to be charged at a constant voltage at the charge cut-off voltage until the current reached 0.05C, and then discharged at 1 / 3C to 50% SOC. After standing for 5 minutes, they were pulse-discharged at 3C for 30 seconds.

[0204] The voltage was recorded before and after each pulse discharge, and the DCR under different conditions was calculated. The calculation formula was DCR = (voltage before pulse discharge after standing still - voltage before standing still after pulse discharge) / pulse current.

[0205] 7. Battery energy density test method The battery cells prepared in each embodiment and comparative example were left at 25°C for 2 hours to ensure that the temperature of the battery cells was 25°C. After charging the battery cells at 1 / 3C to a charge cut-off voltage of 4.25V at 25°C, constant voltage charging was continued at the charge cut-off voltage until the current reached 0.05C and the charge was cut off (where C represents the rated capacity of the battery cells). After the battery cell pool was left at 25°C for 1 hour, the battery cells were discharged at 0.33C at 25°C to a discharge cut-off voltage of 2.8V, and the total discharge energy of the battery cells was recorded as E0.

[0206] Measure the length, width and height of the battery cell, and calculate the volume value V0 of the battery cell = length × width × height.

[0207] The volume energy density of a battery cell = battery cell discharge energy E0 / battery cell volume V0.

[0208] The battery cells of each embodiment and comparative example were prepared according to the above method. The specific parameters and performances are shown in Tables 1 and 2 below. Table 1

[0209] By comparing the examples and the comparative examples, it can be seen that by controlling the D V90 The particle D is 16 μm-25 μm, and particles D are arranged between the positive electrode film layer and the positive electrode current collector. V90 The bottom coating is 3 μm-8 μm, and the positive electrode film layer also includes a carbon nanotube conductive agent. While the battery has a higher energy density, it can improve the problem of burrs on the positive electrode sheet during the slitting process, and at the same time reduce the deterioration of the brittleness of the electrode sheet caused by the addition of the bottom coating, thereby comprehensively improving the safety of the battery.

[0210] Table 2

[0211] By comparing Examples 1 and 12 to 16, it can be seen that when the binder content in the positive electrode film layer is 0.7%-1.3%, the bonding force and brittleness of the positive electrode sheet, the DC internal resistance and energy density of the battery are balanced, further improving the safety and polarization problems that may occur during the battery cycle.

[0212] By comparing Examples 1 and 17, it can be seen that lithium manganese iron phosphate as the bottom coating material is more conducive to improving the battery energy density. By comparing Examples 1 and 18, it can be seen that the nickel-cobalt-manganese ternary material system and the nickel-cobalt-aluminum ternary material system have the ability to achieve higher battery energy density and optimize brittleness.

[0213] 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 the same effect as 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, comprising a positive electrode plate, characterized in that: The positive electrode sheet comprises a positive electrode current collector, a positive electrode film layer disposed on at least one side of the positive electrode current collector, and a primer layer disposed between the positive electrode current collector and at least one side of the positive electrode film layer; the positive electrode film layer comprises a positive electrode active material and a positive electrode film layer conductive agent, The D of the particles in the positive electrode film layer V90 16μm-25μm; The D of the particles in the base coating V90 3μm-8μm; The positive electrode film layer conductive agent includes a carbon nanotube conductive agent.

2. The battery cell according to claim 1, characterized in that: Based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent is 0.3%-0.8%.

3. The battery cell according to claim 1, characterized in that: Based on the total mass of the positive electrode film layer, the mass content of the carbon nanotube conductive agent is 0.4%-0.7%.

4. The battery cell according to claim 1, characterized in that: The positive electrode film layer also includes a binder. Based on the total mass of the positive electrode film layer, the mass proportion of the binder is 0.6%-1.5%.

5. The battery cell according to claim 4, characterized in that: Based on the total mass of the positive electrode film layer, the mass proportion of the binder is 0.7%-1.3%.

6. The battery cell according to claim 1, characterized in that: The D of the particles in the base coating V90 4μm-7μm.

7. The battery cell according to claim 1, characterized in that: The positive electrode active material comprises a lithium-containing transition metal oxide, and based on the total molar number of transition metals in the lithium-containing transition metal oxide, the molar proportion of nickel element in the lithium-containing transition metal oxide is 80%-95%.

8. The battery cell according to claim 1, characterized in that: The positive electrode active material includes a component having the following general formula: Li a Ni x Co y M1 z M2 w O 2-b , wherein M1 includes one or more of Mn and Al, and M2 includes one or more of Zr, B, Mg, Ti, W, Mo, Nb, Ta, Sr, Sb, and K; 0.8≤a≤1.2, 0.8≤x≤1, 0 <y≤0.2,0<z≤0.2,0≤w≤0.1,-0.1≤b≤0.1。 9. The battery cell according to claim 1, characterized in that: The D of the particles in the positive electrode film layer V50 5μm-12μm, (D V90 -D V10 ) / D V50 It is 0.5-3.

10. The battery cell according to claim 1, characterized in that: The positive electrode active material includes single crystal particles and polycrystalline particles, and the mass ratio of the single crystal particles to the polycrystalline particles is 4:6-2:

8.

11. The battery cell according to claim 1, characterized in that: The carbon nanotube conductive agent includes one or more of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

12. The battery cell according to claim 1, characterized in that: The positive electrode film layer conductive agent also includes a spherical conductive agent, and the spherical conductive agent includes one or more of Super-P, acetylene black, and Ketjen black.

13. The battery cell according to claim 4 or 5, characterized in that: The adhesive includes at least one of a water-based adhesive, a biological adhesive, a polyimide adhesive, and a polyurethane adhesive.

14. The battery cell according to claim 4 or 5, characterized in that: The binder includes polyvinylidene fluoride.

15. The battery cell according to claim 1, characterized in that: The primer layer includes polyanionic particles, and the polyanionic particles include components having 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 0.9≤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.

16. The battery cell according to claim 15, characterized in that: The polyanion particles include one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium fluoride phosphate, lithium manganese iron phosphate and modified materials thereof.

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

18. The battery cell according to claim 1, characterized in that: The base coating layer includes a base coating conductive agent, and the base coating conductive agent includes one or more of conductive carbon black and carbon nanotubes.

19. The battery cell according to claim 1, characterized in that: The thickness of the positive electrode current collector is 7 μm-15 μm.

20. The battery cell according to claim 1, characterized in that: The thickness of the primer layer on one side is 5 μm to 25 μm.

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

22. The battery cell according to claim 1, characterized in that: The compaction density of the positive electrode film layer in the full discharge state is 3.40 g / cm 3 -3.60g / cm 3 .

23. A battery device, characterized in that: The battery device comprises the battery cell according to any one of claims 1 to 22, and the battery device comprises at least one of a battery module, a battery pack, and an energy storage device.

24. An electrical device, characterized in that: The invention comprises the battery cell according to any one of claims 1 to 22 or the battery device according to claim 23.

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