Lithium-ion battery and electrical apparatus

Abstract

A battery cell, a battery, an electrical apparatus, and a battery cell core, belonging to the technical field of batteries. When the length-width ratio m of a positive electrode sheet satisfies 1 ≤m≤6 and the compaction density ρ of a positive electrode active material layer satisfies 3.3 g / cm3≤ρ≤3.7 g / cm3, the mass ratio of single-crystal particles of the positive electrode active material is controlled to be no less than 50%, and the porosity of the positive electrode active material layer is controlled to be 23% to 33%. Since single-crystal particles are less prone to fracture during cold pressing and long-term charging / discharging processes, excessive active specific surface area is not exposed compared to polycrystalline particles, thereby reducing side reactions with an electrolyte and reducing the increase of positive electrode impedance in a battery. Moreover, the occurrence of the situation in which an effective conductive network cannot be established at a new interface due to material particle fracture is reduced, so that the phenomenon of local potential increase caused by a particle "island" formed by the positive electrode active material is prevented, thereby achieving mitigation of the DCR in a battery cell core and mitigation of the electrode sheet resistance of a high-energy-density battery cell core.

Description

Lithium ion battery and electric device

[0001] Cross-reference to related applications

[0002] The present application claims priority to the Chinese Invention Patent Application No. 2024105372485, filed on April 30, 2024, and entitled "Battery Cell, Battery, Electric Device and Battery Cell", the contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the technical field of battery, in particular to a lithium ion battery and an electric device. BACKGROUND

[0004] In the jelly-roll battery cell with large length-width ratio of the electrode tab and large compaction density of the electrode tab, due to the influence of the length of the electrode tab, the internal structure of the electrode tab and the conductive network, the positive electrode tab may have uneven current distribution, large resistance and deteriorated dynamics during use of the battery cell.

[0005] SUMMARY

[0006] In view of the above problems, the present application provides a lithium ion battery and an electric device, which can improve the problem of large resistance of the electrode tab of the high energy density battery cell.

[0007] In a first aspect, the present application provides a lithium ion battery, the lithium ion battery comprising a positive electrode tab, a length-width ratio m of the positive electrode tab satisfying 1≤m≤6, the positive electrode tab comprising a positive electrode active material layer, a compaction density p of the positive electrode active material layer satisfying 3.3g / cm 3 ≤p≤3.7g / cm 3 , the positive electrode active material layer comprising a positive electrode active material, the positive electrode active material comprising single crystal particles, a mass fraction of the single crystal particles in the positive electrode active material being not less than 50%, and a porosity of the positive electrode active material layer being 23% to 33%.

[0008] In the technical solution of the present application, when the length-width ratio m of the positive electrode tab satisfies 1≤m≤6 and the compaction density p of the positive electrode active material layer satisfies 3.3g / cm 3 ≤p≤3.7g / cm 3 , the mass fraction of the single crystal particles in the positive electrode active material is controlled to be not less than 50%. Since the single crystal particles are not prone to breakage during cold pressing and long-term charging and discharging, compared to the polycrystal particles, the single crystal particles do not expose too much active specific surface area, thereby reducing the side reaction with the electrolyte and reducing the increase of the positive electrode impedance of the battery. At the same time, the situation that the new interface cannot establish an effective conductive network due to the breakage of the material particles is reduced, and the phenomenon that the local potential increases due to the formation of "island" of the positive electrode active material particles is avoided, thereby improving the DCR of the battery cell and improving the resistance of the electrode tab of the high energy density battery cell.

[0009] In some embodiments, the length-width ratio m of the positive electrode sheet and the positive active material layer compaction density p in g / cm 3 satisfies m x p > 3.

[0010] In the above implementation process, by controlling the mass percentage of single crystal particles of the positive active material to be not less than 50% when the product of the length-width ratio of the positive electrode sheet and the positive active material layer compaction density is greater than 3, the single crystal particles are not prone to breakage during cold pressing and long-term charging and discharging, and compared with polycrystal particles, the single crystal particles do not expose too much active specific surface area, thereby reducing the side reaction with the electrolyte and reducing the increase of the positive electrode impedance of the battery. At the same time, the situation that the new interface cannot establish an effective conductive network due to the breakage of the material particles is reduced, and the phenomenon that the local potential increases due to the formation of particle "islands" of the positive active material is avoided, thereby improving the DCR of the battery cell and improving the sheet resistance of the high-energy-density battery cell.

[0011] In some embodiments, the length-width ratio m of the positive electrode sheet and the positive active material layer compaction density p in g / cm 3 satisfies 3 < m x p < 5, the positive active material includes single crystal particles and polycrystal particles, and the mass percentage of the polycrystal particles in the positive active material is < 50%.

[0012] In the above implementation process, when the length-width ratio m of the positive electrode sheet and the positive active material layer compaction density p in g / cm 3 satisfies 3 < m x p < 5, the sheet resistance of the positive electrode sheet can be improved with a certain amount of polycrystal particles. The use of single crystal particles and polycrystal particles in combination and the control of the use percentage of single crystal particles being greater than that of polycrystal particles can improve the sheet resistance of the positive electrode sheet, and the performance of polycrystal particles can also be utilized, the rate performance of the positive electrode sheet is considered, in addition, the particle size of polycrystal particles is often greater than that of single crystal particles, and the combination of the two realizes the combination of particle sizes, which is beneficial to the improvement of the compaction density and the increase of the energy density.

[0013] In some embodiments, the length-width ratio m of the positive electrode sheet and the positive active material layer compaction density p in g / cm 3 satisfies 3 < m x p < 5, the positive active material includes single crystal particles and polycrystal particles, and the mass percentage of the polycrystal particles in the positive active material is < 30%.

[0014] In the above implementation process, when the length-width ratio m of the positive electrode sheet and the positive active material layer compaction density p in g / cm 3 satisfies 3 < m x p < 5, the use of polycrystal particles is further reduced, which is more conducive to the improvement of the sheet resistance of the positive electrode sheet.

[0015] In some embodiments, the length-width ratio m of the positive electrode sheet and the positive electrode active material layer compaction density ρ in units of g / cm 3 satisfies m×ρ≥5, and the positive electrode active material is single crystal particles.

[0016] In the above implementation process, when the length-width ratio m of the positive electrode sheet and the positive electrode active material layer compaction density ρ in units of g / cm 3 satisfies m×ρ≥5, the positive electrode active material completely adopts single crystal particles, so that the resistance of the positive electrode sheet is better controlled.

[0017] In some embodiments, the length-width ratio m of the positive electrode sheet and the positive electrode active material layer compaction density ρ in units of g / cm 3 satisfies 15≥m×ρ≥5, and the positive electrode active material is single crystal particles.

[0018] In the above implementation process, the positive electrode active material completely adopts single crystal particles, which is especially beneficial to the improvement of the resistance of the positive electrode sheet when the length-width ratio m of the positive electrode sheet and the positive electrode active material layer compaction density ρ in units of g / cm 3 satisfies 15≥m×ρ≥5.

[0019] In some embodiments, the lithium ion battery further comprises a positive electrode tab, each positive electrode sheet is connected to at least one positive electrode tab, and the total length W1 of the connection between a single positive electrode sheet and the corresponding at least one positive electrode tab and the width W of the positive electrode sheet satisfy: W≤W1.

[0020] In the above implementation process, the longer the total length of the connection between the positive electrode sheet and its corresponding connected positive electrode tab, the more beneficial to the overcurrent capacity of the positive electrode sheet. By controlling the total length W1 of the connection between a single positive electrode sheet and the corresponding at least one positive electrode tab and the width W of the positive electrode sheet satisfy: W≤W1, the positive electrode sheet has sufficient overcurrent capacity, which is beneficial to the uniform distribution of the current density of the positive electrode sheet, and further improves the resistance of the positive electrode sheet.

[0021] In some embodiments, the lithium ion battery further comprises a shell, and the total thickness T1 of the positive electrode active material layer of all positive electrode sheets in the lithium ion battery and the width W2 of the inner cavity of the shell satisfy: T1:W2=35%~45%; and / or

[0022] The positive electrode sheet comprises a positive electrode current collector, and the thickness of the positive electrode current collector is ≥8μm.

[0023] In the above implementation process, by controlling the total thickness T1 of the positive electrode active material layer of all positive electrode sheets and the width W2 of the inner cavity of the shell satisfy: T1:W2=35%~45% and the thickness of the positive electrode current collector is ≥8μm, the battery can have better energy density while the positive electrode sheet has smaller resistance.

[0024] In some embodiments, the porosity of the positive electrode active material layer is 23% to 33%.

[0025] In the above implementation process, by controlling the porosity of the positive electrode active material layer to be 23% to 33%, the wettability of the positive electrode sheet when applied as a battery is improved, the electrochemical polarization of the positive electrode sheet is reduced, and thus the kinetic performance of the positive electrode sheet is improved, and the resistance of the positive electrode sheet is improved.

[0026] In some embodiments, the positive electrode active material includes Li x Ni a Co b M c O 2-y A y , wherein x is 0.2 to 1.2, 0.8≤a<1, 0≤b≤0.2, a+b+c=1, 0≤y<0.2, M includes Al and / or Mn, and A includes at least one of S, N, F, Cl, Br, and I.

[0027] In the above implementation process, the better compaction density is conducive to improving the energy density of the battery, and the ternary system material with high nickel content has a high true density, so using it as the positive electrode active material is conducive to improving the energy density of the battery. At the same time, the ternary system material with a nickel content of 0.8≤a<1 has a high gram capacity, which can also effectively improve the gram capacity of the positive electrode active material layer.

[0028] In some embodiments, the mass content of Ni on the surface of the single crystal particles is lower than the mass content of Ni inside the single crystal particles; and / or

[0029] The positive electrode active material includes polycrystalline particles, and the mass content of Ni on the surface of the primary particles in the polycrystalline particles is lower than the mass content of Ni inside the primary particles.

[0030] In the above implementation process, by designing the gradient Ni content of the single crystal particles and / or the primary particles of the polycrystalline particles, the Ni content near the surface of the particles is lower, which can reduce the interface side reaction, and the Ni content near the inside of the particles is higher, which is conducive to the capacity of the particles.

[0031] In some embodiments, the single crystal particles include large single crystal particles and small single crystal particles, the median particle size Dv50 of the large single crystal particles is 5 to 10 μm, and the median particle size Dv50 of the small single crystal particles is 1 to 3.5 μm; and / or

[0032] The particle size distribution SPAN value of the single crystal particles is 1.0 to 2.0; and / or

[0033] The Dv2 of the single crystal particles is greater than 0.7 μm.

[0034] In the above implementation process, through the cooperation of large single crystal particles and small single crystal particles, the compaction density of the positive plate can be improved, especially the compaction density of the positive plate in the case of pure single crystal particles, thereby making the battery have higher energy density. By controlling the particle size distribution SPAN value of the single crystal particles to be 1.0-2.0 and the Dv2 of the single crystal particles to be greater than 0.7 μm, the slurry of the positive active material has better stability during the preparation of the positive plate, and is not easy to produce gel. The single crystal particles have strong dispersing ability, which is beneficial to the uniform distribution of the positive active material and the conductive agent in the prepared positive active material layer, thereby forming a good conductive network.

[0035] In some embodiments, the lithium ion battery further includes a negative plate, the negative plate includes a negative active material layer, the negative active material layer includes graphite and a silicon material, and the mass of the silicon material accounts for 5%-15% of the mass of the graphite.

[0036] In the above implementation process, the silicon material has high specific capacity. By adding the silicon material in the negative active material layer, the total weight of the active material of the negative plate can be effectively reduced. Compared with the pure graphite system negative plate, the weight per unit area of the silicon-doped negative plate is significantly reduced, the thickness of the negative plate is thinned, the kinetic performance is improved, the resistance of the negative plate is improved, and the energy density of the battery is also improved.

[0037] In some embodiments, the silicon material includes at least one of silicon oxide, silicon carbon, and pre-lithiated silicon; and / or

[0038] The median particle size Dv50 of the silicon material is 6-15 μm.

[0039] In the above implementation process, by controlling the median particle size Dv50 of the silicon material to be 6-15 μm, the diffusion path of lithium ions can be effectively shortened, thereby improving the resistance of the negative plate.

[0040] In some embodiments, the negative plate includes a negative current collector, the negative active material layer is attached to the negative current collector, the negative active material layer includes a first negative active material layer and a second negative active material layer, the first negative active material layer is arranged between the negative current collector and the second negative active material layer, and the silicon material is arranged in the second negative active material layer; and / or

[0041] The compaction density of the negative active material layer is ≤1.70 g / cm 3 .

[0042] In the above implementation process, by placing the silicon material in the outer layer, the silicon material can increase the porosity of the negative plate, and the silicon material particles in the upper layer can preferentially embed lithium, effectively shorten the transmission path of Li + , and reduce the concentration polarization of the negative plate. By controlling the compaction density of the negative active material layer to be ≤1.70 g / cm 3The negative plate has good porosity, effectively increases the conduction path of lithium ions, and realizes the improvement of the kinetics of the negative plate and the resistance.

[0043] In a second aspect, the application provides a lithium ion battery, the lithium ion battery comprising a positive plate, a positive tab, a shell and a negative plate, the positive plate comprising a positive active material layer, the positive active material layer comprising a positive active material, a length-width ratio m of the positive plate and a positive active material layer compact density ρ in g / cm 3 The positive active material comprises single crystal particles, and the mass percentage of the single crystal particles in the positive active material is not less than 50%; each positive plate is connected with at least one positive tab, and the total length W1 of the connection between a single positive plate and at least one positive tab and the width W of the positive plate satisfy W≤W1; the total thickness T1 of the positive active material layer of all the positive plates in the lithium ion battery and the width W2 of the inner cavity of the shell satisfy T1:W2=35%~45%; and the negative plate comprises a negative active material layer, the negative active material layer comprises graphite and a silicon material, and the silicon material accounts for 5%~15% of the graphite.

[0044] In the technical scheme of the embodiments of the application, when the product of the length-width ratio of the positive plate and the positive active material layer compact density is greater than 3, the mass percentage of the single crystal particles in the positive active material is controlled to be not less than 50%. Since the single crystal particles are not prone to breakage in the process of cold pressing and long-term charging and discharging, using more single crystal particles is conducive to reducing the possibility of side reactions of the positive active material, and further reducing the occurrence of the loss of the conductive network of the positive active material layer, the formation of particle "islands" and the increase of local potential, thereby realizing the improvement of the resistance of the positive plate. By controlling the total length W1 of the connection between a single positive plate and at least one positive tab and the width W of the positive plate to satisfy W≤W1, the positive plate has sufficient current-carrying capacity, which is conducive to the uniform distribution of the current density of the positive plate, and further improves the resistance of the positive plate. By controlling the total thickness T1 of the positive active material layer of all the positive plates and the width W2 of the inner cavity of the shell to satisfy T1:W2=35%~45% and the thickness of the positive current collector being greater than or equal to 8μm, the battery has good energy density on the premise of the positive plate having small resistance.

[0045] In a third aspect, the application provides a power-using device, the power-using device comprising the lithium ion battery provided in the first aspect or the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0046] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The detailed description is made with reference to the accompanying drawings.

[0047] FIG. 1 is a structural schematic diagram of a vehicle according to some embodiments of the present application;

[0048] FIG. 2 is an exploded structural schematic diagram of a secondary battery according to some embodiments of the present application;

[0049] FIG. 3 is a structural schematic diagram of a battery cell according to some embodiments of the present application;

[0050] FIG. 4 is an exploded view of a battery cell according to some embodiments of the present application;

[0051] FIG. 5 is a structural schematic diagram of an electrode assembly according to some embodiments of the present application;

[0052] FIG. 6 is a first structural schematic diagram of a positive electrode sheet according to some embodiments of the present application;

[0053] FIG. 7 is a second structural schematic diagram of a positive electrode sheet according to some embodiments of the present application;

[0054] FIG. 8 is a third structural schematic diagram of a positive electrode sheet according to some embodiments of the present application;

[0055] FIG. 9 is a first structural schematic diagram of a negative electrode sheet according to some embodiments of the present application;

[0056] FIG. 10 is a second structural schematic diagram of a negative electrode sheet according to some embodiments of the present application;

[0057] FIG. 11 is a flowchart of a method for manufacturing a positive electrode sheet according to some embodiments of the present application.

[0058] Reference signs in the detailed description of the embodiments are as follows:

[0059] 1000 - vehicle; 100 - secondary battery; 200 - motor; 300 - controller; 10 - case; 11 - accommodation space; 12 - first portion; 13 - second portion; 20 - battery cell; 21 - housing; 211 - opening; 22 - end cap assembly; 221 - end cap; 222 - electrode terminal; 23 - electrode assembly; 231 - positive electrode sheet; 2311 - positive electrode current collector; 2312 - positive electrode active material layer; 2313 - positive electrode tab; 232 - negative electrode sheet; 2321 - negative electrode current collector; 2322 - negative electrode active material layer; 2322a - first negative electrode active material layer; 2322b - second negative electrode active material layer; 233 - separator; 24 - current collecting member; 25 - insulating protector. DETAILED DESCRIPTION

[0060] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, but cannot limit the protection scope of the present application.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof. The description herein of any embodiments, including preferred embodiments, is not intended to be limiting. Various

[0062] In the description of the embodiments of the present application, the technical terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0063] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification is not necessarily all referring to the same embodiment, or to a particular embodiment, or to a particular set of embodiments. It will be explicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0064] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A existing alone, A and B existing together, and B existing alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0065] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0066] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0067] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, can also be detachable connection, or integral; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through an intermediate medium, can be internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0068] At present, from the development of market situation, the application of power battery is more and more widely. Power battery is not only applied to energy storage power supply system of hydropower, thermal power, wind power and solar power station, but also widely used in electric bicycles, electric motorcycles, electric vehicles and other electric vehicles, military equipment, aerospace and other fields. With the continuous expansion of the application field of power battery, the market demand is also increasing.

[0069] The power battery can be a lithium ion battery. The lithium ion battery has a very wide application in the field of portable electronic devices, electric vehicles, etc. The greater the length-width ratio of the battery pole piece, the more conducive to the improvement of the grouping efficiency of the module / battery pack, thereby making the module / battery pack have higher electric quantity. At the same time, the greater the compaction density of the battery pole piece, the more conducive to the capacity of the battery. In order to pursue better performance, the length-width ratio and the compaction density of the pole piece of the battery are large. The greater the length-width ratio of the pole piece, the more prone to current / potential unevenness and larger resistance in the length direction of the pole piece. The higher the coating thickness and compaction density of the pole piece, the worse the kinetic performance of the system.

[0070] Based on the above consideration, in order to improve the pole piece resistance, the present application provides a lithium ion battery, which comprises a positive pole piece, the positive pole piece comprises a positive active material layer, the positive active material layer comprises a positive active material, the length-width ratio m of the positive pole piece and the compaction density p of the positive active material layer with g / cm 3 The unit is not less than 50%.

[0071] In such a lithium ion battery, by controlling the single crystal particle mass ratio of the positive electrode active material to be not less than 50% when the product of the aspect ratio of the positive electrode sheet and the positive electrode active material layer compaction density is greater than 3, that is, when the aspect ratio is large, the compaction density is large, or both the aspect ratio and the compaction density are large, the single crystal particles are not prone to breakage during cold pressing and long-term charging and discharging, and compared to polycrystal particles, the single crystal particles do not expose too much active specific surface area, thereby reducing the side reaction with the electrolyte and reducing the increase in the positive electrode impedance of the battery. At the same time, the situation that the new interface cannot establish an effective conductive network due to the breakage of the material particles is reduced, the phenomenon that the local potential increases due to the formation of particle "islands" of the positive electrode active material is avoided, the improvement of the DCR of the battery cell is achieved, and the improvement of the sheet resistance is achieved.

[0072] The lithium ion battery can be used in, but is not limited to, an electric device such as a vehicle, a ship, or an aircraft.

[0073] The electric device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric vehicle, an electric automobile, a ship, a spacecraft, and the like. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric automobile toy, an electric ship toy, and an electric aircraft toy, and the like. The spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, and the like.

[0074] The following embodiments are described by taking a vehicle 1000 as an example for convenience of description.

[0075] Please refer to FIG. 1, which is a structural schematic diagram of the vehicle 1000 provided by some embodiments of the present application. The vehicle 1000 can be a fuel automobile, a gas automobile, or a new energy automobile. The new energy automobile can be a pure electric automobile, a hybrid electric automobile, or a range extended automobile. The vehicle 1000 is internally provided with a secondary battery 100, which can be arranged at the bottom, the head, or the tail of the vehicle 1000. The secondary battery 100 can be used for power supply of the vehicle 1000, for example, the secondary battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further include a controller 300 and a motor 200. The controller 300 is used to control the secondary battery 100 to supply power to the motor 200, for example, to meet the working power demand of the vehicle 1000 during starting, navigation, and driving.

[0076] In some embodiments of the present application, the secondary battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0077] In the present application, the secondary battery 100 can refer to a single battery cell 20, or a single physical module including a plurality of battery cells 20 to provide higher voltage and capacity, which can be in the form of a battery pack, a battery module, etc. The secondary battery 100 can include a case 10 to package the plurality of battery cells 20, and the case 10 can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells 20.

[0078] FIG. 2 is an exploded structural schematic view of a secondary battery 100 according to some embodiments of the present application. Referring to FIG. 2, the secondary battery 100 includes a case 10 and a battery cell 20, and the battery cell 20 is accommodated in the case 10.

[0079] The case 10 is used to provide an accommodation space 11 for the battery cell 20. In some embodiments, the case 10 can include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 are coupled to each other to define the accommodation space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a sealing member (not shown in the figure), which can be a sealing ring, sealing glue, etc.

[0080] The first portion 12 and the second portion 13 can be in various shapes, such as a cuboid, a cylinder, etc. The first portion 12 can be a hollow structure with one side open to form an accommodation cavity for accommodating the battery cell 20, and the second portion 13 can also be a hollow structure with one side open to form an accommodation cavity for accommodating the battery cell 20, and the open side of the second portion 13 is coupled to the open side of the first portion 12 to form the case 10 with the accommodation space 11. Of course, as shown in FIG. 2, the first portion 12 can be a hollow structure with one side open, and the second portion 13 can be a plate-shaped structure, and the second portion 13 is coupled to the open side of the first portion 12 to form the case 10 with the accommodation space 11.

[0081] In the secondary battery 100, there are a plurality of battery cells 20, and the plurality of battery cells 20 can be connected in series, in parallel, or in a mixed connection, where the mixed connection means that some of the plurality of battery cells 20 are connected in series and some are connected in parallel. The plurality of battery cells 20 can be directly connected in series, in parallel, or in a mixed connection, and then the whole is accommodated in the case 10; of course, the plurality of battery cells 20 can first be connected in series, in parallel, or in a mixed connection to form a battery module, and then a plurality of battery modules are connected in series, in parallel, or in a mixed connection to form a whole, which is accommodated in the case 10. The battery cell 20 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes, etc. FIG. 2 exemplarily shows the case where the battery cell 20 is in the shape of a square.

[0082] In some embodiments, the secondary battery 100 can further include a busbar component (not shown in the figure), and the plurality of battery cells 20 can be electrically connected through the busbar component to achieve series connection, parallel connection or mixed connection of the plurality of battery cells 20.

[0083] FIG. 3 is a structural schematic diagram of the battery cell 20 according to some embodiments of the present application, and FIG. 4 is an exploded view of the battery cell 20 according to some embodiments of the present application. Referring to FIGS. 3 and 4, the battery cell 20 can include a housing 21, an end cap assembly 22 and an electrode assembly 23. The housing 21 has an opening 211, the electrode assembly 23 is accommodated in the housing 21, and the end cap assembly 22 is used to cover the opening 211.

[0084] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a cuboid structure, the housing 21 can also be a cuboid structure. FIGS. 3 and 4 exemplarily show the case where the housing 21 and the electrode assembly 23 are square.

[0085] The material of the housing 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiments of the present application do not make special limitations thereon.

[0086] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to cover the opening 211 of the housing 21 to form a sealed mounting space (not shown in the figure), and the mounting space is used to accommodate the electrode assembly 23. The mounting space is also used to accommodate an electrolyte, such as an electrolyte solution. As a component for outputting the electrical energy of the electrode assembly 23, the electrode terminal 222 in the end cap assembly 22 is used to be electrically connected with the electrode assembly 23, i.e., the electrode terminal 222 is electrically connected with the tab of the electrode assembly 23, for example, the electrode terminal 222 is connected with the tab through a current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0087] It should be noted that the opening 211 of the housing 21 can be one or two. If the opening 211 of the housing 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to be electrically connected with the positive tab 2313 and the negative tab of the electrode assembly 23. If the opening 211 of the housing 21 is two, for example, the two openings 211 are provided at opposite sides of the housing 21, and the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the housing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal 222 used to be electrically connected with the positive tab 2313 of the electrode assembly 23, and the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal 222 used to be electrically connected with the negative tab 232 of the electrode assembly 23.

[0088] In some embodiments, as shown in FIG. 4, the battery cell 20 can further include an insulating protection member 25 fixed to the outer periphery of the electrode assembly 23, which is used to insulate and isolate the electrode assembly 23 from the shell 21. For example, the insulating protection member 25 is an adhesive tape adhered to the outer periphery of the electrode assembly 23. In some embodiments, the number of electrode assemblies 23 is multiple, and the insulating protection member 25 is arranged around the outer periphery of the multiple electrode assemblies 23 and forms an integral structure with the multiple electrode assemblies 23 to maintain the structural stability of the electrode assembly 23.

[0089] As shown in FIG. 5, the electrode assembly 23 includes a positive electrode sheet 231, a negative electrode sheet 232, and a separator 233. The positive electrode sheet 231 includes a positive electrode current collector 2311 and a positive electrode active material layer 2312 coated on the surface of the positive electrode current collector 2311. The positive electrode current collector 2311 without the positive electrode active material layer 2312 protrudes from the positive electrode current collector 2311 with the positive electrode active material layer 2312, and serves as a positive electrode tab 2313.

[0090] The negative electrode sheet 232 includes a negative electrode current collector 2321 and a negative electrode active material layer 2322 coated on the surface of the negative electrode current collector 2321. The negative electrode current collector 2321 without the negative electrode active material layer 2322 protrudes from the negative electrode current collector 2321 with the negative electrode active material layer 2322, and serves as a negative electrode tab. The material of the negative electrode current collector 2321 can be copper, and the negative electrode active material can be carbon or silicon, etc. In order to ensure that no fuse occurs when passing a large current, the number of positive electrode tabs 2313 is multiple and stacked together, and the number of negative electrode tabs is multiple and stacked together. The material of the separator 233 can be PP (polypropylene) or PE (polyethylene), etc. In addition, the electrode assembly 23 can be a laminated electrode assembly, and the embodiments of the present application are not limited thereto.

[0091] FIG. 3 is a structural schematic diagram of a lithium ion battery cell according to some embodiments of the present application. As shown in FIG. 3, the lithium ion battery includes a positive electrode sheet 231, and the length-width ratio m of the positive electrode sheet satisfies 1≤m≤6. FIG. 6 is a first structural schematic diagram of the positive electrode sheet 231 according to some embodiments of the present application. FIG. 7 is a second structural schematic diagram of the positive electrode sheet 231 according to some embodiments of the present application. FIG. 8 is a third structural schematic diagram of the positive electrode sheet 231 according to some embodiments of the present application. As shown in FIGS. 6, 7 and 8, the positive electrode sheet 231 includes a positive electrode active material layer 2312, and the compaction density p of the positive electrode active material layer 2312 satisfies 3.3g / cm3≤p≤4.5g / cm3. 3≤ p ≤ 3.7 g / cm 3 The positive electrode active material layer 2312 comprises a positive electrode active material, and the positive electrode active material comprises single crystal particles, and the mass percentage of the single crystal particles in the positive electrode active material is not less than 50%.

[0092] The positive electrode active material layer 2312 is attached to at least part of the surface of the positive electrode current collector 2311, and the material of the positive electrode current collector 2311 can be one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. Please refer to FIG. 6, in an embodiment, the positive electrode active material layer 2312 is arranged on one surface of the positive electrode current collector 2311; please refer to FIG. 7, in another embodiment, the positive electrode active material layer 2312 is arranged on both surfaces of the positive electrode current collector 2311.

[0093] For a lithium ion battery, the positive electrode active material in the positive electrode active material layer 2312 refers to a substance capable of intercalating and deintercalating lithium ions.

[0094] When the battery is a stacked design, the calculation of the aspect ratio m of the positive electrode sheet 231 is based on any one of the positive electrode sheets, and if there is a heterogeneous structure, the aspect ratios of multiple positive electrode sheets are measured and averaged; the aspect ratio m of the positive electrode sheet 231 can be calculated by the length L of the positive electrode sheet 231 and the width W of the positive electrode sheet 231, and the calculation method can be m = L / W. It should be noted that the measurement of L and W does not include the tab part. The compaction density p of the positive electrode active material layer 2312 can be calculated by the unit area weight C (mg / cm 2 ), the thickness T (μm) of the positive electrode sheet 231, and the thickness T0 (μm) of the current collector, and the calculation method can be p = C / (T-T0). The product m x p of the aspect ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 in units of g / cm 3

[0095] The single crystal particle refers to a single particle without or almost without agglomeration.

[0096] For the test of the mass percentage of the single crystal particles in the positive electrode active material in the positive electrode sheet, Micro-CT can be used to non-destructively scan the multi-layer positive electrode sheet to obtain a microscopic image, and the average value is calculated according to the area percentage of the single crystal particles and the polycrystal particles in the image, which can be regarded as the ratio of the single crystal particles to the polycrystal particles.

[0097] By meeting 1 ≤ m ≤ 6 for the aspect ratio m of the positive electrode sheet 231 and 3.3 g / cm 3 ≤ p ≤ 3.7 g / cm 3 ​At this stage, the mass ratio of single-crystal particles in the positive electrode active material is controlled to be no less than 50%. Since single-crystal particles are less prone to breakage during cold pressing and long-term charge-discharge processes, they do not expose excessive active surface area compared to polycrystalline particles, thus reducing side reactions with the electrolyte and decreasing the increase in positive electrode impedance. Simultaneously, it reduces the possibility of new interfaces failing to establish an effective conductive network due to particle breakage, avoiding the formation of particle "islands" in the positive electrode active material that lead to increased local potential. This improves the cell's DCR and the electrode resistance of high-energy-density cells.

[0098] For example, the aspect ratio m of the positive electrode sheet satisfies 1 ≤ m ≤ 6 and the compaction density ρ of the positive electrode active material layer satisfies 3.3 g / cm³. 3 ≤ρ≤3.7g / cm 3 When the mass percentage of single crystal particles in the positive electrode active material can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, and 100%, it can also be any value within the range of not less than 50%.

[0099] In some embodiments of this application, the aspect ratio m of the positive electrode and the ratio in g / cm 3 The compaction density ρ of the positive electrode active material layer, expressed in units of m×ρ≥3, satisfies this condition.

[0100] By controlling the product of the aspect ratio of the positive electrode sheet and the compaction density of the positive electrode active material to be greater than 3, and ensuring that the mass ratio of single-crystal particles in the positive electrode active material is not less than 50%, the single-crystal particles are less prone to breakage during cold pressing and long-term charge-discharge processes. Compared to polycrystalline particles, they do not expose excessive active surface area, thereby reducing side reactions with the electrolyte and decreasing the increase in positive electrode impedance. Simultaneously, it reduces the situation where new interfaces cannot establish an effective conductive network due to particle breakage, avoiding the phenomenon of particle "islands" in the positive electrode active material leading to increased local potential. This improves the cell's DCR and the electrode resistance of high-energy-density cells.

[0101] In some embodiments of this application, the aspect ratio m of the positive electrode 231 and the ratio in g / cm 3 The compaction density ρ of the positive electrode active material layer 2312, measured in units, satisfies 3≤m×ρ<5. The positive electrode active material includes single crystal particles and polycrystalline particles, and the mass proportion of polycrystalline particles in the positive electrode active material is ≤50%.

[0102] Polycrystalline particles refer to secondary particles, that is, particles formed by the aggregation of multiple single crystal particles.

[0103] The aspect ratio m of the positive electrode 231 and the g / cm 3When the positive electrode active material layer 2312 has a compaction density p of 3≤m×p<5, the use of a certain amount of polycrystal particles can still improve the resistance of the electrode sheet. The use of single crystal particles and polycrystal particles in combination and the control of the use proportion of single crystal particles being greater than that of polycrystal particles can achieve good improvement of the resistance of the electrode sheet, and also play the performance of polycrystal particles, taking into account the rate performance of the positive electrode sheet 231. In addition, the particle size of polycrystal particles is often greater than that of single crystal particles. In some embodiments, the particle size of polycrystal particles is greater than that of single crystal particles. The use of the two in combination achieves the combination of particle sizes, which is beneficial to the improvement of the compaction density and the increase of the energy density.

[0104] For example, when the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, the mass proportion of the polycrystal particles in the positive electrode active material can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and the like. It can also be any value within the range of not more than 50%. 3 For example, when the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, the mass proportion of the polycrystal particles in the positive electrode active material can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and the like. It can also be any value within the range of not more than 50%.

[0105] In the technical solutions of some embodiments of the present application, the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, and the positive electrode active material includes single crystal particles and polycrystal particles. The mass proportion of the polycrystal particles in the positive electrode active material is ≤30%. 3 In the technical solutions of some embodiments of the present application, the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, and the positive electrode active material includes single crystal particles and polycrystal particles. The mass proportion of the polycrystal particles in the positive electrode active material is ≤30%. 3 For example, when the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, the mass proportion of the polycrystal particles in the positive electrode active material can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and the like. It can also be any value within the range of not more than 50%.

[0106] In the technical solutions of some embodiments of the present application, the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, and the positive electrode active material includes single crystal particles and polycrystal particles. The mass proportion of the polycrystal particles in the positive electrode active material is ≤30%. 3 In the technical solutions of some embodiments of the present application, the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, and the positive electrode active material includes single crystal particles and polycrystal particles. The mass proportion of the polycrystal particles in the positive electrode active material is ≤30%. 3 For example, when the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, the mass proportion of the polycrystal particles in the positive electrode active material can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, and the like. It can also be any value within the range of not more than 50%.

[0107] In the technical solutions of some embodiments of the present application, the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, and the positive electrode active material includes single crystal particles and polycrystal particles. The mass proportion of the polycrystal particles in the positive electrode active material is ≤30%. 3 In the technical solutions of some embodiments of the present application, the length-width ratio m of the positive electrode sheet 231 and the compaction density p of the positive electrode active material layer 2312 are 3≤m×p<5, and the positive electrode active material includes single crystal particles and polycrystal particles. The mass proportion of the polycrystal particles in the positive electrode active material is ≤30%. 3The positive electrode active material layer 2312 has a compaction density p satisfying 15≥m×p≥5, and the resistance of the positive electrode sheet 231 is improved.

[0108] In the technical solution of some embodiments of the present application, the lithium ion battery further comprises a positive electrode tab 2313, each positive electrode sheet 231 is connected to at least one positive electrode tab 2313, and the total length W1 of the connection between a single positive electrode sheet 231 and at least one positive electrode tab 2313 and the width W of the positive electrode sheet 231 satisfy W≤W1.

[0109] The connection between each positive electrode sheet 231 and at least one positive electrode tab 2313 means that each positive electrode sheet 231 is connected to at least one positive electrode tab 2313, for example, one positive electrode sheet 231 can be connected to one positive electrode tab 2313, two positive electrode tabs 2313, three positive electrode tabs 2313, four positive electrode tabs 2313, etc.

[0110] The total length W1 of the connection between a single positive electrode sheet 231 and at least one corresponding positive electrode tab 2313 and the width W of the positive electrode sheet 231 satisfy W≤W1 means that the total length of the connection between all positive electrode tabs 2313 connected to the same positive electrode sheet 231 and the positive electrode sheet 231 is not less than the width of the positive electrode sheet 231, wherein the connection between the positive electrode tab 2313 and the positive electrode sheet 231 refers to the junction of the positive electrode sheet 231 and the positive electrode tab 2313, that is, the bottom of the positive electrode tab 2313. For example, when only one positive electrode tab 2313 is connected to the positive electrode sheet 231, the positive electrode sheet 231 is connected to the positive electrode tab 2313 on one side (long side or short side), the width of the positive electrode tab 2313 is the same as the width of the positive electrode sheet, that is, the positive electrode sheet 231 is in a full-tab state. When two positive electrode tabs 2313 are connected to the positive electrode sheet 231, the two positive electrode tabs 2313 can be arranged on opposite sides or adjacent sides of the positive electrode sheet 231, and the positive electrode tabs 2313 can be arranged at the center of the side of the positive electrode sheet 231 or at any position of the side of the positive electrode sheet 231.

[0111] The longer the total length of the connection between the positive electrode sheet 231 and its corresponding positive electrode tab 2313, the more conducive to the overcurrent capacity of the positive electrode sheet 231. By controlling the total length W1 of the connection between a single positive electrode sheet 231 and at least one positive electrode tab 2313 and the width W of the positive electrode sheet 231 satisfy W≤W1, the positive electrode sheet 231 has sufficient overcurrent capacity, which is conducive to the uniform distribution of the current density of the positive electrode sheet 231, thereby improving the resistance of the positive electrode sheet 231.

[0112] In the technical scheme of some embodiments of the present application, the lithium ion battery further comprises a shell, and the total thickness T1 of the positive active material layer 2312 of all the positive electrode sheets 231 in the lithium ion battery and the width W2 of the inner cavity of the shell satisfy the relationship T1:W2=35%-45%; the positive electrode sheet 231 comprises a positive electrode current collector 2311, and the thickness of the positive electrode current collector 2311 is greater than or equal to 8 μm.

[0113] The total thickness T1 of the positive active material layer 2312 of all the positive electrode sheets 231 in the lithium ion battery can be obtained by calculating the number N of the positive electrode sheets 231, the thickness T of the positive electrode sheet 231, and the thickness T0 of the positive electrode current collector 2311, and the calculation method can be T1=N×(T-T0).

[0114] The resistance of the lithium ion battery is related to the number of layers of the positive electrode sheet 231 inside the lithium ion battery. In the lithium ion battery of the same system and size, the more the number of layers of the positive electrode sheet 231, the smaller the resistance. At the same time, the type and thickness of the current collector used also affect the resistance of the lithium ion battery to a certain extent. Generally, using a thicker current collector can improve the resistance. Therefore, the more the number of layers of the positive electrode sheet 231 and the greater the thickness of the current collector, the more favorable it is for the resistance of the lithium ion battery, but a larger number of layers and a larger thickness of the current collector have a certain negative impact on the energy density of the lithium ion battery. By controlling the total thickness T1 of the positive active material layer 2312 of all the positive electrode sheets 231 and the width W2 of the inner cavity of the shell to satisfy the relationship T1:W2=35%-45% and the thickness of the positive electrode current collector 2311 to be greater than or equal to 8 μm, the lithium ion battery can have a good energy density while the positive electrode sheet 231 has a small resistance.

[0115] For example, the ratio of the total thickness T1 of the positive active material layer 2312 of all the positive electrode sheets 231 in the lithium ion battery to the width W2 of the inner cavity of the shell can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, or 45%, or any value within the range of 35%-45%. The thickness of the positive electrode current collector 2311 can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 19 μm, or 20 μm, or any value greater than or equal to 8 μm.

[0116] In the technical scheme of some embodiments of the present application, the porosity of the positive active material layer 2312 is 23%-33%.

[0117] The porosity refers to the percentage of the pore volume in the block material to the total volume of the material in the natural state. The porosity of the positive electrode active material layer 2312 can be obtained by the gas replacement method, and reference is made to GB / T24586-2009, the porosity P=(V1-V2) / V1*100%, wherein V1 is the apparent volume of the electrode sheet, and V2 is the true volume of the electrode sheet.

[0118] The porosity of the positive electrode sheet 231 affects the distribution of the internal electrolyte of the positive electrode sheet 231. The smaller the porosity, the more difficult it is for the electrolyte to be distributed, and uneven distribution of the electrolyte will worsen the electrochemical polarization of the positive electrode sheet 231, thereby affecting the resistance of the electrode sheet. Meanwhile, the smaller the porosity of the positive electrode sheet 231, the greater the compaction density of the positive electrode sheet 231, and the greater the compaction density, the more beneficial it is to the energy density of the battery. By controlling the porosity of the positive electrode active material layer 2312 to be 23% to 33%, the wettability of the positive electrode sheet 231 when applied as a battery is improved, the electrochemical polarization of the positive electrode sheet 231 is reduced, and thus the kinetic performance of the positive electrode sheet 231 is improved, and the resistance of the positive electrode sheet 231 is improved. At the same time, the energy density of the battery can also be taken into account.

[0119] For example, the porosity of the positive electrode active material layer 2312 can be 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, or 33%, and the like, and it can also be any value in the range of 23% to 33%.

[0120] In the technical solution of some embodiments of the present application, the positive electrode active material includes a ternary system material, and the general formula is Li x Ni a Co b M c O 2-y A y , wherein x is 0.2 to 1.2, 0.8≤a<1, 0≤b≤0.2, a+b+c=1, 0≤y<0.2, M includes Al and / or Mn, and A includes at least one of S, N, F, Cl, Br, and I.

[0121] The ternary system material generally includes NCMA, NCA, and NCM, and the like. Among them, NCA is widely used because of its long service life, large capacity, and high energy density, but its specific heat capacity is relatively low; NCM combines the advantages of lithium cobaltate, lithium nickelate, and lithium manganate, and has obvious ternary synergistic effect. NCM can generally be represented as: LiNi x Co y Mn z O2.

[0122] The content of Ni of the positive electrode active material is tested as follows: 0.4 g of the positive electrode active material layer 2312 powder of the electrode sheet is taken into a 25 ml beaker, 2 ml to 5 ml of nitric acid is added, and the mixture is left overnight, and then is placed on an electric heating plate to be heated at about 100°C (the input voltage is adjusted by a voltage regulator transformer to control the temperature), until the powder is digested, 0.5 ml of perchloric acid is added, and the mixture is heated and digested at about 140°C until white smoke stops coming out, and the residue should be white, otherwise the nitric acid and perchloric acid should be added again for repeated digestion, finally, 7% (referring to the volume % of the acid, the same below) hydrochloric acid is used for dissolution and extraction, and the volume is adjusted to an appropriate volume according to the content of the element to be tested, and then the ICP-OES testing instrument is started to test the content of Ni.

[0123] The electrode sheet has a good compaction density, which is beneficial to improve the energy density of the battery, and the ternary system material with high nickel content has a high true density, and can fill more active substances per unit volume, so that the ternary system material is used as the positive electrode active material, which is beneficial to improve the energy density of the battery. At the same time, the ternary system material with 0.8≤a<1 has a high gram capacity, which can also effectively improve the energy density of the battery.

[0124] It should be noted that the above limitation of x includes the molar content of Li under different charge and discharge states of the battery (usually the voltage of the battery is between 2-5V).

[0125] It can be understood that the battery will be accompanied by lithium (Li) deintercalation and consumption during charging and discharging, and the content of Li in the positive electrode sheet of the battery is different when the battery is discharged to different states, wherein the content of Li can be measured by molar content, but is not limited thereto. At the same time, the positive electrode material applied to the positive electrode sheet of the battery system will change the content of Li in the positive electrode material contained in the electrode sheet after charging and discharging cycle. In the enumeration of the positive electrode material in the present application, the content of Li is the initial state of the material unless otherwise specified. As for "the content of Li is the initial state of the material", the initial state of the material refers to the state before the material is put into the positive electrode slurry or the state of the battery after full discharge in the specified charging and discharging interval (at this time, lithium ions are embedded into the positive electrode as much as possible). It can be understood that the new material obtained by properly modifying the listed positive electrode material is also within the scope of the positive electrode material, and the foregoing proper modification refers to acceptable modification methods for the positive electrode material, and non-limiting examples include coating modification.

[0126] In the enumeration of the positive electrode material in the present application, the content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the change of the molar content of oxygen, and the actual content of O will fluctuate. The content of O can be measured by molar content, but is not limited thereto.

[0127] In some embodiments of the technical solutions of the present application, in some embodiments, the mass content of Ni on the surface of the single crystal particles is lower than the mass content of Ni in the interior of the single crystal particles; the positive electrode active material comprises polycrystal particles, and the mass content of Ni on the surface of the primary particles in the polycrystal particles is lower than the mass content of Ni in the interior of the primary particles.

[0128] The surface layer of the single crystal particles and / or the polycrystal particles has a large contact area with the electrolyte, and is more likely to cause particle breakage, side reactions and the like, and the Ni 2+ dissolution, Li+ / Ni 2+ mixing and the like are more serious. By designing the gradient Ni content of the primary particles of the single crystal particles and / or the polycrystal particles, the Ni content near the surface of the particles is lower, which can reduce the interface side reactions, and the Ni content near the interior of the particles is higher, which is beneficial to the capacity of the particles.

[0129] In some embodiments of the technical solutions of the present application, the single crystal particles comprise large single crystal particles and small single crystal particles, the median particle size Dv50 of the large single crystal particles is 5-10 μm, and the median particle size Dv50 of the small single crystal particles is 1-3.5 μm.

[0130] The median particle size Dv50 is the particle size corresponding to 50% of the cumulative amount in the volume particle size cumulative distribution graph. The volume particle size cumulative distribution graph, also known as the differential distribution graph of the particle size, is a curve drawn with the particle size as the horizontal coordinate and the content differential distribution of the particle size in different sizes as the vertical coordinate, which can accurately reflect the particle size distribution characteristics of the material particles. Among them, the volume particle size distribution of the material can be measured by using a laser particle size analyzer, and an interval particle size distribution curve can be drawn. When measuring the median particle sizes of the large single crystal particles and the small single crystal particles in the active material layer of the positive electrode sheet 231, the positive electrode active material layer 2312 can be removed, sintered at 600°C in an oxygen atmosphere in a tube furnace for 3h, and the conductive carbon and the binder are removed to obtain the powder material of the positive electrode active material layer 2312, and the powder material is dried and then detected by using a laser particle size analyzer of a type of Mastersizer3000 to obtain a volume particle size cumulative distribution graph. The median particle sizes of the large single crystal particles and the small single crystal particles can be obtained according to the peaks in the volume particle size cumulative distribution graph.

[0131] The median particle size Dv50 of the large single crystal particles refers to that the large single crystal particles are accumulated from small to large, and when the accumulation reaches 50% of the total volume, the particle size of the large single crystal particles at this time is the median particle size Dv50. The median particle size Dv50 of the small single crystal particles refers to that the small single crystal particles are accumulated from small to large, and when the accumulation reaches 50% of the total volume, the particle size of the small single crystal particles at this time is the median particle size Dv50.

[0132] Through the cooperation of large single crystal particles and small single crystal particles, the compaction density of the positive plate 231 can be improved, especially the compaction density of the positive plate 231 in the case of pure single crystal particles, and thus the battery has a higher energy density.

[0133] For example, the median particle size Dv50 of the large single crystal particles can be 5 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, 8.2 μm, 8.4 μm, 8.6 μm, 8.8 μm, 9 μm, 9.2 μm, 9.4 μm, 9.6 μm, 9.8 μm, or 10 μm, etc., and can also be any value in the range of 7-10 μm. The median particle size Dv50 of the small single crystal particles can be 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, or 3.5 μm, etc., and can also be any value in the range of 1-3.5 μm.

[0134] In the technical solutions of some embodiments of the present application, the particle size distribution SPAN value of the single crystal particles is 1.0-2.0.

[0135] The SPAN value refers to the particle size span value, which can be obtained by the formula SPAN=(Dv90-Dv10) / Dv50.

[0136] By controlling the particle size distribution SPAN value of the single crystal particles to be 1.0-2.0, the slurry of the positive active material has better stability during the preparation of the positive plate 231, and is not prone to gelation. The single crystal particles have strong dispersing ability, which is conducive to the uniform distribution of the positive active material and the conductive agent in the positive active material layer 2312 formed, and thus a good conductive network is formed.

[0137] For example, the particle size distribution SPAN value of the single crystal particles can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0, etc., and can also be any value in the range of 1.0-2.0.

[0138] In the technical solutions of some embodiments of the present application, the Dv2 of the single crystal particles is greater than 0.7 μm.

[0139] The Dv2 of the single crystal particles refers to: the single crystal particles are accumulated from small to large, and when the accumulation reaches 2% of the total volume, the particle size of the single crystal particles at this time is the Dv2 thereof.

[0140] By controlling the Dv2 of the single crystal particles to be greater than 0.7 μm, the slurry of the positive active material has better stability during preparation of the positive sheet 231, and is not prone to gelation. The single crystal particles have strong dispersing ability, and are conducive to uniform distribution of the positive active material and the conductive agent in the positive active material layer 2312, thereby forming a better conductive network.

[0141] For example, the Dv2 of the single crystal particles can be 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm, or any value in the range greater than 0.7 μm.

[0142] In the technical solution of some embodiments of the present application, the lithium ion battery further includes a negative sheet 232, and the negative sheet 232 includes a negative active material layer 2322. The negative active material layer 2322 includes graphite and silicon material, and the mass of the silicon material accounts for 5% to 15% of the mass of the graphite.

[0143] The silicon material has relatively high specific capacity. By adding the silicon material to the negative active material layer 2322, the total weight of the active material of the negative electrode can be effectively reduced. Compared with a pure graphite system negative electrode, the unit area weight of the silicon-doped negative sheet 232 is significantly reduced, the thickness of the negative sheet 232 is thinned, the kinetic performance is improved, the resistance of the negative sheet 232 is improved, and the energy density of the battery is also improved.

[0144] For example, the mass of the silicon material can account for 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% of the mass of the graphite, or any value in the range of 5% to 15%.

[0145] In the technical solution of some embodiments of the present application, the silicon material includes at least one of silicon oxide, silicon carbon, and pre-lithiated silicon, and the median particle size Dv50 of the silicon material is 6 to 15 μm.

[0146] From the perspective of optimizing the transmission path of lithium ions, the solid-phase diffusion of pre-lithiated silicon is better than other types of silicon materials, which can better improve the kinetics and optimize the resistance of the positive electrode. Of course, from the perspective of optimizing other electrical properties of the lithium ion battery, other silicon materials can have better performance than pre-lithiated silicon. Therefore, those skilled in the art can understand that the selection of the silicon material can be based on the actual situation and the required electrical properties.

[0147] The median particle size Dv50 of the silicon material refers to: the silicon material is accumulated from small to large, and when the accumulation accounts for 50% of the total volume, the particle size of the silicon material at this time is the median particle size Dv50.

[0148] By controlling the median particle size Dv50 of the silicon material to be 6-15 μm, the diffusion path of lithium ions can be effectively shortened, and the resistance of the negative electrode sheet 232 can be improved.

[0149] For example, the median particle size Dv50 of the silicon material can be 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, or 15 μm, etc. It can also be any value in the range of 6-15 μm.

[0150] FIG. 9 is a first structural schematic diagram of the negative electrode sheet 232 according to some embodiments of the present application, and FIG. 10 is a second structural schematic diagram of the negative electrode sheet 232 according to some embodiments of the present application. Referring to FIGS. 9 and 10, in the technical solution of some embodiments of the present application, the negative electrode sheet 232 includes a negative electrode current collector 2321, and a negative electrode active material layer 2322 attached to the negative electrode current collector 2321. The negative electrode active material layer 2322 includes a first negative electrode active material layer 2322a and a second negative electrode active material layer 2322b. The first negative electrode active material layer 2322a is arranged between the negative electrode current collector 2321 and the second negative electrode active material layer 2322b, and the silicon material is arranged in the second negative electrode active material layer 2322b. The compaction density of the negative electrode active material layer 2322 is ≤1.70 g / cm3.

[0151] The material of the negative electrode current collector 2321 can be one or more of copper and copper alloys. The negative electrode active material layer 2322 attached to the negative electrode current collector 2321 can be, for example, referring to FIG. 9, that a first negative electrode active material layer 2322a and a second negative electrode active material layer 2322b are sequentially arranged on one surface of the negative electrode current collector 2321; or, for example, referring to FIG. 10, that a first negative electrode active material layer 2322a and a second negative electrode active material layer 2322b are sequentially arranged on both surfaces of the negative electrode current collector 2321.

[0152] By placing the silicon material entirely in the outer layer, the silicon material can increase the porosity of the negative electrode sheet 232, and the silicon material particles in the upper layer can preferentially intercalate lithium, effectively shortening the transmission path of Li + , and reducing the concentration polarization of the negative electrode sheet 232. By controlling the compaction density of the negative electrode active material layer 2322 to be ≤1.70 g / cm 3 , the negative electrode sheet 232 has good porosity, effectively increasing the conduction path of lithium ions, and achieving the improvement of the kinetics and resistance of the negative electrode sheet 232.

[0153] After the foregoing introduces the materials and structure of the lithium ion battery, the preparation method of the lithium ion battery will be specifically introduced below.

[0154] The preparation method of the lithium ion battery comprises the following steps: determining the aspect ratio of the positive electrode sheet 231 and the target compaction density of the positive electrode active material layer 2312, and then selecting the single crystal particle proportion in the positive electrode active material layer 2312 according to the relationship between the product of the aspect ratio and the compaction density and the single crystal particle proportion, wherein the relationship between the single crystal particle proportion, the aspect ratio of the positive electrode sheet 231 and the target compaction density of the positive electrode active material layer 2312 satisfies: when the product of the aspect ratio m of the positive electrode sheet 231 and the compaction density ρ of the positive electrode active material layer 2312 is greater than 3, the positive electrode active material comprises single crystal particles, and the mass proportion of the single crystal particles in the positive electrode active material is not less than 50%. 3 When the product of the aspect ratio m of the positive electrode sheet 231 and the compaction density ρ of the positive electrode active material layer 2312 is greater than 3, the positive electrode active material comprises single crystal particles, and the mass proportion of the single crystal particles in the positive electrode active material is not less than 50%. The single crystal particles and other raw materials are prepared into a slurry, the slurry is coated on the positive electrode current collector 2311 to obtain the positive electrode sheet 231, and then the positive electrode sheet 231, the separator, the negative electrode sheet 232, the separator, and the like are sequentially stacked to form a laminated electrode assembly 23. Then, the electrode assembly 23 is placed in a shell, and an electrolyte is injected to form a lithium ion battery.

[0155] The method controls the mass proportion of the single crystal particles in the positive electrode active material to be not less than 50% when the product of the aspect ratio of the positive electrode sheet 231 and the compaction density of the positive electrode active material layer 2312 is greater than 3. Since the single crystal particles are not easy to break during cold pressing and long-term charging and discharging, using more single crystal particles is conducive to reducing the possibility of side reactions of the positive electrode active material, thereby reducing the occurrence of the loss of the conductive network of the positive electrode active material layer 2312, the formation of particle “islands” and the increase of local potential, and achieving the improvement of the resistance of the electrode sheet.

[0156] FIG. 11 is a flowchart of a preparation method of a lithium ion battery provided by some embodiments of the present application. Referring to FIG. 11, the present application provides a preparation method of a lithium ion battery, which comprises the following steps:

[0157] S110, preparing a positive electrode active slurry: dispersing the positive electrode active material, the binder and the conductive agent in a solvent to form a positive electrode active slurry. The positive electrode active material can be the positive electrode active material described above, for example: LiNi x Co y Mn z O2, (0≤x≤1、0≤y≤1、0≤z≤1、x+y+z=1) of a ternary system material, and a small amount of other positive electrode active materials can be optionally added. The mass proportion of the single crystal particles in the positive electrode active material is determined according to the aspect ratio of the positive electrode sheet 231 and the target compaction density of the positive electrode active material layer 2312, and the specific relationship satisfies: when the product of the aspect ratio m of the positive electrode sheet 231 and the compaction density ρ of the positive electrode active material layer 2312 is greater than 3, the positive electrode active material comprises single crystal particles, and the mass proportion of the single crystal particles in the positive electrode active material is not less than 50%. 3When the product of the unitized positive electrode active material layer 2312 compaction density p is m x p ≥ 3, the mass ratio of single-crystal particles in the positive electrode active material is not less than 50%.

[0158] For the specific selection of the ternary system material, reference can be made to the selection of the ternary system material in the positive electrode active material layer 2312 in the positive electrode sheet 231 as described above, which will not be repeated here.

[0159] The binder can be one or more of styrene butadiene rubber, water-based acrylic resin, carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-vinyl acetate copolymer, polyvinyl alcohol, and polyvinyl butyral. The conductive agent can be at least one of conductive carbon black, carbon fiber, carbon nanotube, ketjen black, graphene, or acetylene black. The solvent can be one or more of dimethyl glutarate and N-methyl pyrrolidone. The first positive electrode active paste can further add a leveling agent, a dispersant, and the like.

[0160] S120, preparing the positive electrode active material layer 2312: coating the positive electrode active paste on the surface of the positive electrode current collector 2311, and then drying to form the positive electrode active material layer 2312. At this time, the coating can be on one surface or both surfaces of the positive electrode current collector 2311 according to the needs.

[0161] The coating method can be, but is not limited to, blade coating, roller coating, slot coating, and the like.

[0162] S130, rolling the positive electrode active material layer 2312 to obtain the positive electrode sheet 231.

[0163] S140, stacking the positive electrode sheet 231, the separator, the negative electrode sheet 232, the separator, and the like in sequence to form the laminated electrode assembly 23.

[0164] S150, assembling the laminated electrode assembly 23 into the battery monomer 20. The battery monomer 20 can be used to prepare the secondary battery 100 and provide electric energy for the electric device.

[0165] One or more embodiments will be described in more detail below with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0166] Examples and Comparative Examples

[0167]

Preparation of the positive electrode sheet

[0168] The positive electrode active material, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) were added to N-methyl pyrrolidone (NMP) at a mass ratio of 96.5:1:2.5, stirred and mixed uniformly to obtain a coating slurry; then the slurry was uniformly coated on the positive electrode current collector aluminum foil, dried, cold-pressed, and cut to obtain the positive electrode sheet.

[0169] Preparation of the negative electrode sheet

[0170] The active material, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickening agent sodium hydroxymethyl cellulose (CMC) were dissolved in the solvent deionized water according to the mass ratio of 90:5:3:2, and the negative electrode slurry was prepared after being mixed uniformly; the negative electrode slurry was coated on the negative electrode current collector copper foil once or multiple times, and the negative electrode sheet was obtained after drying, cold pressing and slitting.

[0171] Preparation of the electrolyte

[0172] In an argon atmosphere glove box (H2O <0.1 ppm, O2 <0.1 ppm), the organic solvent ethylene carbonate (EC) / diethyl carbonate (DEC) / ethyl methyl carbonate (EMC) was mixed uniformly according to the volume ratio of 1 / 1 / 1, 1 mol / L LiPF6 lithium salt was added and uniformly dispersed, and then 5% fluoroethylene carbonate was dissolved in the above-mentioned organic solvent, and the electrolyte was obtained after stirring uniformly.

[0173] Separating membrane

[0174] The polyethylene film was used as the separating membrane.

[0175] Preparation of the battery monomer

[0176] The prepared positive electrode sheet, negative electrode sheet and separating membrane (polyethylene (PE) porous polymer film) were stacked according to the Z-shaped structure to form the corresponding electrode assembly, the electrode assembly was vacuum dried at 90°C for 12h, and then the positive and negative electrode tabs were ultrasonically welded, the positive electrode used aluminum tabs and the negative electrode used nickel tabs, the positive and negative electrode tabs were located on the same side of the electrode assembly, the electrode assembly after welding of the tabs was loaded into an aluminum plastic film of appropriate size for top side sealing, the top side sealing temperature was 145°C, then the electrolyte was injected and sealed, and the uncharged battery was obtained. The uncharged battery was sequentially subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity testing and the like, and the battery monomer was obtained.

[0177] The main parameter controls of the examples and 1 to 33 and the comparative examples 1 to 2 are shown in the following table:

[0178] In the above table, m refers to the length-width ratio of the positive electrode sheet, p refers to the positive electrode active material layer compaction density in g / cm 3 3 3 3 3 In the above table, m refers to the length-width ratio of the positive electrode sheet, p refers to the positive electrode active material layer compaction density in g / cm

[0179] When the number of positive electrode tabs is 2, the two tabs are arranged oppositely.

[0180] LiNi0.90Co0.05Mn0.05O2 0.9 LiNi0.85Co0.05Mn0.10O2 0.07 LiNi0.80Co0.05Mn0.15O2 0.03 LiNi0.75Co0.05Mn0.20O2 0.85 LiNi0.70Co0.05Mn0.25O2 0.10 LiNi0.65Co0.05Mn0.30O2 0.05 LiNi0.60Co0.05Mn0.35O2 0.80 LiNi0.55Co0.05Mn0.40O2 0.12 LiNi0.50Co0.05Mn0.45O2 0.08 LiNi0.45Co0.05Mn0.50O2 0.75 LiNi0.40Co0.05Mn0.55O2 0.15 LiNi0.35Co0.05Mn0.60O2 0.10 LiNi0.30Co0.05Mn0.65O2

[0181] The number of laminations of the electric core of each example and comparative example was 10 layers.

[0182] The batteries provided by each example and comparative example were subjected to performance detection, and the performance detection specifically included: battery initial resistance test: at room temperature 25℃, the battery monomer was discharged to 50% SOC using 1 / 3C1 current, then discharged for 10s using 4C1 current, the open circuit voltage before discharging was recorded as U1, the terminal voltage at the end of discharging was recorded as U2, U2-U1 was recorded as ΔU1, and the ratio of ΔU to current I 4C1 was the initial resistance DCR1 of the battery, that is, DCR1=ΔU1 / I 4C1 . Among them, C1 was the initial capacity of the battery, and the test method included: at 25℃, the monomer battery was first charged to 4.25V at a constant current of 0.33C, then charged to a current of 0.05C at a constant voltage of 4.25V, and then rested for 30min, and then discharged to 2.8V at a constant current of 0.33C, and the discharge capacity was recorded as C1. The specific process of discharging to 50% SOC was: at 25℃, the monomer battery was first charged to 4.25V at a constant current of 0.33C1, then charged to a current of 0.05C1 at a constant voltage of 4.25V, and then rested for 30min, and then discharged at a constant current of 0.33C1.

[0183] Battery resistance test after 200 cycles: at room temperature 25℃, the battery monomer was discharged to 50% SOC, then discharged for 10s using 4C2 current, the open circuit voltage before discharging was recorded as U3, the terminal voltage at the end of discharging was recorded as U4, U4-U2 was recorded as ΔU2, and the ratio of ΔU2 to current I 4C2 was the resistance DCR2, that is, DCR2=ΔU2 / I 4C2C2 is the capacity after 200 cycles of the battery, and the test method comprises: first charging the single battery to 4.25V at a constant current of 0.33C at 25°C, further charging to a current of 0.05C at a constant voltage of 4.25V, standing for 30min, and then discharging the lithium ion battery to 2.8V at a constant current of 0.33C, and the discharge capacity is recorded as C2. The specific process of discharging to 50% SOC is: first charging the single battery to 4.25V at a constant current of 0.33C2 at 25°C, further charging to a current of 0.05C2 at a constant voltage of 4.25V, standing for 30min, and then discharging at a constant current of 0.33C2 to 0.5C2 cutoff.

[0184] The DCR growth rate after 200 cycles is (DCR2-DCR1) / DCR1, which can represent the DCR growth during the cycle process. The greater the DCR growth, the more the battery DCR deteriorates during the cycle process due to the influence of current density grading, conductive network, and battery polarization increase, affecting the battery dynamics performance and cycle life.

[0185] The DCR growth rate after 2000 cycles can be obtained by referring to the DCR growth rate after 200 cycles, wherein DCR2 is the internal resistance after 2000 cycles, and the test process can refer to the internal resistance test of the battery after 200 cycles described above

[0186] Battery volume energy density (VED) test: volume energy density = battery discharge energy / cell volume, wherein the battery discharge energy test comprises: first charging the single battery to 4.25V at a constant current of 0.33C at 25°C, further charging to a current of 0.05C at a constant voltage of 4.25V, standing for 30min, and then discharging the lithium ion battery to 2.8V at a constant current of 0.33C, and the discharge energy is the energy of the battery; the cell volume = cell length x cell width x cell thickness, wherein the size measurement method of the pole piece is as follows: after the full charge cell is disassembled, a piece of cathode pole piece is taken out, soaked in DMC (dimethyl carbonate) for 6h, taken out, dried and measured the size of the cathode pole piece. Length and width can be measured by charge-coupled device (CCD) or ruler, and thickness can be tested by micrometer. By testing the volume energy density of the battery, the energy density level of the cell under the design can be preliminarily characterized. The proportion of single crystal particles and polycrystalline particles does not affect the gram capacity of the material, that is, under the same conditions of m x p, the energy density of the pole piece is the same. The greater the m x p, the higher the energy density of the pole piece, and the cell using this design can also have higher energy density.

[0187] The test results are shown in the following table:

[0188] From the above table, it can be seen that the battery prepared by using the positive plate provided in the application has a smaller initial internal resistance, a lower internal resistance growth rate, and a higher volume energy density.

[0189] From the comparison of the examples and the comparative examples, it can be seen that when the aspect ratio m of the positive plate gradually increases or the compaction density p of the positive active material layer gradually increases, the volume energy density of the battery gradually increases. From the comparison of the data of Examples 1 to 3, Examples 9 to 11, and Comparative Examples 1 to 2, it can be seen that when m x p of the positive plate is greater than 3, the volume energy density of the positive plate is greater than 709.7 Wh / L. From the comparison of Examples 4 to 8, it can be seen that when the aspect ratio m of the positive plate and the compaction density p of the positive active material layer remain unchanged, as the mass proportion of the single-crystal particles of the positive active material increases, the internal resistance growth rate after 200 cycles and 2000 cycles gradually decreases. When the mass proportion of the single-crystal particles is greater than 50%, the internal resistance growth rate after 200 cycles can be controlled to be less than 13.6%, and the internal resistance growth rate after 2000 cycles can be controlled to be less than 33.78%.

[0190] From the comparison of the data of Examples 12 to 15 and Examples 32 to 33, it can also be seen that when the aspect ratio m of the positive plate and the compaction density p of the positive active material layer remain unchanged, as the mass proportion of the single-crystal particles of the positive active material increases, the internal resistance growth rate after 200 cycles and 2000 cycles gradually decreases.

[0191] From the comparison of the data of Examples 1, 4, and 9 and Examples 12, Examples 6, 10, and 13, and Examples 8, 11, and 14, it can be seen that when the aspect ratio m of the positive plate gradually increases or the compaction density p of the positive active material layer gradually increases, the improvement of the single-crystal particles of the same mass proportion on the internal resistance growth rate gradually decreases.

[0192] From the comparison of Examples 12 to 15, it can be seen that when m x p increases to 6.6, only when the mass proportion of the single-crystal particles is large can the internal resistance growth rate be significantly improved. When the positive active material is pure single-crystal particles, the internal resistance growth rate after 200 cycles can be controlled to be about 5%, and the internal resistance growth rate after 2000 cycles can be controlled to be about 17.5%.

[0193] From the comparison of Examples 15 to 21, it can be seen that when m x p increases to more than 6.6, the improvement of the pure single-crystal particles of the positive active material on the internal resistance growth rate gradually weakens. When m x p is less than 15, the internal resistance growth rate after 200 cycles can be controlled to be less than 7.7%, and the internal resistance growth rate after 2000 cycles can be controlled to be less than 25.7%.

[0194] It can be obtained by comparing example 20 and example 22 to 23 that the internal resistance growth rate gradually decreases with the gradual increase of the total length W1 of the single positive electrode sheet and the corresponding at least one positive electrode tab connection. And when W1 = W, the internal resistance growth rate after 200 cycles can be controlled within 20.8%, and the internal resistance growth rate after 2000 cycles is below 57.7%.

[0195] It can be obtained by comparing example 22 and example 24 that the internal resistance growth rate decreases with the increase of the number of tabs.

[0196] It can be obtained by comparing example 12 and example 25 to 27 that the volume energy density of the battery increases with the increase of the nickel content of the positive electrode active material, and when the nickel content is above 85%, the volume energy density of the battery is above 772.4 Wh / L.

[0197] It can be obtained by comparing example 12 and example 28 to 32 that the addition of silicon carbon in the negative electrode active material can improve the volume energy density of the battery, and the volume energy density of the battery gradually increases with the increase of the amount of silicon carbon in the negative electrode active material.

[0198] The above is only a specific embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery includes a positive electrode sheet, an aspect ratio m of the positive electrode sheet satisfies 1≤m≤6, the positive electrode sheet includes a positive electrode active material layer, a compaction density p of the positive electrode active material layer satisfies 3.3g / cm 3 ≤p≤3.7g / cm 3 , the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes single crystal particles, a mass proportion of the single crystal particles in the positive electrode active material is not less than 50%, and a porosity of the positive electrode active material layer is 23% to 33%.

2. The lithium-ion battery of claim 1, wherein, The aspect ratio m of the positive electrode sheet and the positive electrode active material layer packing density ρ in g / cm 3 satisfy m x ρ ≥ 3.

3. The lithium-ion battery of claim 2, wherein, The aspect ratio m and the positive electrode active material layer packing density p in g / cm 3 satisfy 3 ≤ m x p < 5, the positive electrode active material includes single-crystal particles and polycrystal particles, and the mass ratio of the polycrystal particles in the positive electrode active material is ≤ 50%.

4. The lithium-ion battery of claim 3, wherein, The aspect ratio m and the positive electrode active material layer packing density p in g / cm 3 satisfy 3 ≤ m x p < 5, the positive electrode active material includes single-crystal particles and polycrystal particles, and the mass ratio of the polycrystal particles in the positive electrode active material is ≤ 30%.

5. The lithium-ion battery of claim 2, wherein, The aspect ratio m of the positive electrode sheet and the positive electrode active material layer packing density p in g / cm 3 satisfy m x p ≥ 5, the positive electrode active material being single crystal particles.

6. The lithium-ion battery of claim 5, wherein, The aspect ratio m of the positive electrode sheet and the positive electrode active material layer packing density p in g / cm 3 satisfy 15 ≥ m x p ≥ 5, the positive electrode active material being single crystal particles.

7. The lithium-ion battery of any one of claims 1 to 6, wherein, The lithium ion battery further comprises a positive tab, each of the positive tab and at least one of the positive tab are connected, the total length W1 of the single positive tab and the corresponding at least one positive tab and the width W of the positive tab satisfy: W≤W1.

8. The lithium-ion battery of any one of claims 1 to 6, wherein, The lithium ion battery further comprises a shell, the total thickness T1 of the positive active material layer of all positive tabs in the lithium ion battery and the width W2 of the inner cavity of the shell satisfy: T1:W2=35%~45%; and / or The positive tab comprises a positive current collector, and the thickness of the positive current collector is ≥8μm.

9. The lithium-ion battery of any one of claims 1 to 6, wherein, The positive electrode active material includes Li x Ni a Co b M c O 2-y A y wherein x is 0.2 to 1.2, 0.8≤a<1, 0≤b≤0.2, a+b+c=1, 0≤y<0.2, M includes Al and / or Mn, and A includes at least one of S, N, F, Cl, Br, and I.

10. The lithium-ion battery of any one of claims 1 to 6, wherein, The mass content of Ni on the surface of the single crystal particles is lower than that of the internal Ni; and / or The positive active material comprises polycrystal particles, and the mass content of Ni on the surface of the primary particles in the polycrystal particles is lower than that of the internal Ni.

11. The lithium-ion battery of any one of claims 1 to 6, wherein, The single crystal particles comprise large single crystal particles and small single crystal particles, the median particle size Dv50 of the large single crystal particles is 5~10μm, and the median particle size Dv50 of the small single crystal particles is 1~3.5μm; and / or The particle size distribution SPAN value of the single crystal particles is 1.0~2.0; and / or The Dv2 of the single crystal particles is >0.7μm.

12. The lithium-ion battery of any one of claims 1 to 6, wherein, The lithium ion battery further comprises a negative tab, the negative tab comprises a negative active material layer, the negative active material layer comprises graphite and a silicon material, and the mass of the silicon material accounts for 5%~15% of the mass of the graphite.

13. The lithium-ion battery of claim 12, wherein, The silicon material comprises at least one of silicon oxide, silicon carbon and pre-lithiated silicon; and / or The median particle size Dv50 of the silicon material is 6~15μm.

14. The lithium-ion battery of claim 12, wherein, The negative tab comprises a negative current collector, the negative active material layer is attached to the negative current collector, the negative active material layer comprises a first negative active material layer and a second negative active material layer, the first negative active material layer is arranged between the negative current collector and the second negative active material layer, and the silicon material is arranged in the second negative active material layer; and / or The compacted density of the negative active material layer is ≤ 1.70 g / cm 3 .

15. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode sheet, a positive electrode tab, a shell and a negative electrode sheet, the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a positive electrode active material, the length-width ratio m of the positive electrode sheet and the positive electrode active material layer compaction density ρ in g / cm 3 The positive electrode active material layer compaction density ρ is greater than or equal to 3, the positive electrode active material comprises single crystal particles, the mass percentage of the single crystal particles in the positive electrode active material is not less than 50%; each positive electrode sheet is connected with at least one positive electrode tab, the total length W1 of the single positive electrode sheet and at least one positive electrode tab connection and the width W of the positive electrode sheet satisfy: W≤W1; the total thickness T1 of the positive electrode active material layer of all positive electrode sheets in the lithium ion battery and the width W2 of the inner cavity of the shell satisfy: T1: W2=35%-45%; the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises graphite and a silicon material, the silicon material accounts for 5%-15% of the graphite.

16. An electrical device, comprising: The electric device comprises the lithium ion battery according to any one of claims 1 to 15.

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