Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprises a first film layer and a second film layer arranged between the first film layer and the negative electrode current collector, the first film layer comprises a first negative electrode active material, and the second film layer comprises a second negative electrode active material. The first negative electrode active material comprises a first graphite material, and the ID / IG of the first graphite material is 0.5-0.9; the second film layer comprises a second negative electrode active material, the second negative electrode active material comprises a second graphite material, and the ID / IG of the second graphite material is 0.05-0.2; wherein ID represents the D peak intensity of the Raman spectrum at 1350 + / -50 cm <-1 >, and IG represents the G peak intensity of the Raman spectrum at 1580 + / -50 cm <-1 >. The secondary battery gives consideration to the fast charging performance and the service life of the battery.

Description

[0001] Divisional Explanation The present disclosure is based on and claims priority to Chinese Patent Application No. 202510932455.5, filed on July 7, 2025, entitled “Secondary Battery and Power-Consuming Device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to a secondary battery and a power-consuming device. BACKGROUND

[0003] In recent years, with the increasingly wide application of secondary batteries, secondary batteries are widely used in energy storage power supply systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc.

[0004] Due to the great development of secondary batteries, higher requirements are put forward for the fast charging performance and battery life of secondary batteries. However, during the fast charging process of the battery, lithium ions will deposit on the surface of the negative electrode to form a metal layer, reducing the number of lithium ions inside the battery and shortening the service life of the battery.

[0005] Therefore, how to balance the fast charging performance and service life of the battery has become a technical problem to be solved. SUMMARY

[0006] The present application is made in view of the above-mentioned problems, and aims to provide a secondary battery and a power-consuming device, which balance the fast charging performance and service life of the battery.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a secondary battery, comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a first film layer and a second film layer arranged between the first film layer and the negative electrode current collector, the first film layer comprising a first negative electrode active material, the first negative electrode active material comprising a first graphite material, the I D / I G of the first graphite material is 0.5 to 0.9; the second film layer comprises a second negative electrode active material, the second negative electrode active material comprising a second graphite material, the I D / I G of the second graphite material is 0.05 to 0.2; wherein I D represents the D peak intensity of the Raman spectrum at 1350±50 cm -1 , and I G represents the G peak intensity of the Raman spectrum at 1580±50 cm -1G peak intensity. The I D / I G of the first graphite material in the present application is 0.5 to 0.9, indicating that there are a large number of defects on the surface of the first graphite material, which can serve as additional active sites for lithium ion intercalation. By arranging the first graphite material with more surface defects on the outer layer (first film layer) of the negative electrode sheet, the contact probability of the additional active sites with the electrolyte can be increased, thereby improving the fast charging performance of the battery. On this basis, the second graphite material with I D / I G of 0.05 to 0.2 is used in the inner layer (second film layer) of the negative electrode sheet. The second graphite material has fewer surface defects and a relatively complete structure, which is beneficial to reducing the irreversible loss of lithium ions, thereby prolonging the service life of the battery.

[0008] In some embodiments, the volume average particle size Dv50 of the first graphite material is 9.2 μm to 15.5 μm. This is beneficial to the formation of a rich pore structure between the particles of the first graphite material, thereby improving the lithium ion and electron transport performance in the first film layer, and further improving the kinetic performance of the secondary battery. In some embodiments, the volume average particle size Dv50 of the second graphite material is 16.3 μm to 25.5 μm. This is beneficial to improving the compaction density of the second film layer, thereby improving the energy density of the secondary battery. In addition, it is also beneficial to the formation of a rich pore structure between the particles of the second graphite material, improving the lithium ion and electron transport performance in the negative electrode film layer, and further improving the kinetic performance of the secondary battery.

[0009] In some embodiments, the BET specific surface area of the first graphite material is 0.3 m 2 / g to 3 m 2 / g. When the BET specific surface area of the first graphite material is within the above range, the surface of the first graphite material can provide more lithium ion intercalation and deintercalation channels. During the fast charging process, lithium ions can intercalate into the first graphite material more quickly through these channels, reducing the transmission distance and resistance of lithium ions, thereby improving the fast charging performance of the battery. In some embodiments, the BET specific surface area of the second graphite material is 0.5 m 2 / g to 5 m 2 / g. The surface of the second graphite material can thus provide more lithium ion intercalation and deintercalation channels. During the fast charging process, lithium ions can intercalate into the second graphite material more quickly through these channels, reducing the transmission distance and resistance of lithium ions, thereby improving the fast charging performance of the battery.

[0010] In some embodiments, the tap density of the first graphite material is 0.7 g / cm 3 to 1.6 g / cm 3Thus, the first film layer is beneficial to form abundant pore structures, which can ensure the battery to have more excellent fast charging performance. In some embodiments, the tap density of the second graphite material is 0.8 g / cm 3 to 1.5 g / cm 3 Thus, the second graphite material can be closely packed in the second film layer, which is beneficial to accommodate more second graphite material (active material) in the second film layer, thereby improving the energy density of the battery.

[0011] In some embodiments, the first negative electrode active material further comprises a negative electrode coating layer distributed on the surface of the first graphite material, and the negative electrode coating layer comprises amorphous carbon. The structure of the amorphous carbon is relatively loose, and has abundant pore structures. These pores can provide more diffusion channels for lithium ions, shorten the diffusion path of lithium ions in the electrode material, and by arranging the amorphous carbon on the surface of the first graphite material, lithium ions can more quickly pass through the negative electrode coating layer to reach the inside of the first graphite material, thereby improving the fast charging performance of the battery.

[0012] In some embodiments, the thickness of the negative electrode coating layer is 10 nm to 100 nm. The thickness of the negative electrode coating layer is in the above range, which is beneficial to the secondary battery to have both fast charging performance and energy density.

[0013] In some embodiments, the second film layer further comprises the first graphite material. The first graphite material can improve the fast charging performance of the battery. In this embodiment, by arranging the second graphite material and the first graphite material in the second film layer, it is beneficial to improve both the fast charging performance and the service life of the battery.

[0014] In some embodiments, the mass ratio of the second graphite material to the first graphite material in the second film layer is (3-5):(5-7). By controlling the mass ratio of the second graphite material to the first graphite material in the second film layer in the above range, it is beneficial to further improve both the fast charging performance and the service life of the battery.

[0015] In some embodiments, the ratio of the average thickness of the first film layer to the average thickness of the second film layer is (3-5):(5-7). By controlling the ratio of the average thickness of the first film layer to the average thickness of the second film layer in the above range, it is beneficial to further improve both the fast charging performance and the service life of the battery.

[0016] In some embodiments, the first film layer further comprises a first binder, and the first binder comprises at least one of styrene-butadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, or carboxymethyl chitosan. The above substances have high viscosity, and by selecting the above substances as the first binder, the risk of separation of the first film layer from the second film layer can be reduced, thereby being beneficial to further improve the service life of the secondary battery.

[0017] In some embodiments, the second film layer further comprises a second binder, and the second binder comprises at least one of styrene butadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, or carboxymethyl chitosan. The viscosity of the above-mentioned second binder is high, and by selecting the above-mentioned substance as the second binder, the risk of the second film layer being separated from the negative current collector can be reduced, thereby facilitating further improvement of the service life of the secondary battery.

[0018] In some embodiments, the first binder comprises at least one of styrene butadiene rubber, lithium polyacrylate, and polyacrylate. By selecting the above-mentioned substance as the first binder, the fast-charging performance, service life, and energy density of the battery can be taken into account.

[0019] In some embodiments, the second binder comprises at least one of styrene butadiene rubber, lithium polyacrylate, and polyacrylate. By selecting the above-mentioned substance as the second binder, the fast-charging performance, service life, and energy density of the battery can be taken into account.

[0020] In some embodiments, the mass percentage of the first binder in the first film layer is 0.1% to 2%. On the one hand, this is conducive to preventing the first negative active material from pulverizing and falling off, thereby prolonging the service life of the battery. On the other hand, this is conducive to the battery achieving high energy density.

[0021] In some embodiments, the mass percentage of the second binder in the second film layer is 0.1% to 2%. On the one hand, this is conducive to preventing the second negative active material from pulverizing and falling off, thereby prolonging the service life of the battery. On the other hand, this is conducive to the battery achieving high energy density.

[0022] In some embodiments, the first film layer further comprises a first dispersant, and the first dispersant comprises at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose. The above-mentioned substance has high ionic conductivity, and by selecting it as the first dispersant, the fast-charging performance of the battery can be improved.

[0023] In some embodiments, the second film layer further comprises a second dispersant, and the second dispersant comprises at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0024] The above-mentioned substance has high ionic conductivity, and by selecting it as the second dispersant, the fast-charging performance of the battery can be improved.

[0025] In some embodiments, the first dispersant comprises lithium carboxymethyl cellulose. Lithium carboxymethyl cellulose contains lithium ions, which can make up for the loss of active lithium ions caused by the formation of an SEI film during the first charging, thereby improving the first charging efficiency of the battery.

[0026] In some embodiments, the second dispersing agent comprises lithium carboxymethyl cellulose. The lithium carboxymethyl cellulose contains lithium ions, so it can make up for the loss of active lithium ions caused by the formation of SEI film during the first charge, thereby improving the first charge efficiency of the battery.

[0027] In some embodiments, the mass percentage of the first dispersing agent in the first film layer is 0.3% to 1.5%. This is conducive to achieving high energy density of the battery.

[0028] In some embodiments, the mass percentage of the second dispersing agent in the second film layer is 0.3% to 1.5%. This is conducive to achieving high energy density of the battery.

[0029] In some embodiments, the first film layer further comprises a first conductive agent, and the first conductive agent comprises at least one of super conductive carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black. By using the above substances as the first conductive agent, the fast charging performance of the battery can be further improved.

[0030] In some embodiments, the second film layer further comprises a second conductive agent, and the second conductive agent comprises at least one of super conductive carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black. By using the above substances as the second conductive agent, the fast charging performance of the battery can be further improved.

[0031] In some embodiments, the first conductive agent comprises carbon nanotubes and conductive carbon black. This is conducive to further improving the fast charging performance of the battery.

[0032] In some embodiments, the second conductive agent comprises carbon nanotubes and conductive carbon black. This is conducive to further improving the fast charging performance of the battery.

[0033] In some embodiments, the mass percentage of the first conductive agent in the first film layer is 0.1% to 2%. This is conducive to improving the conductivity of the first film layer while also taking into account high energy density.

[0034] In some embodiments, the mass percentage of the second conductive agent in the second film layer is 0.1% to 2%. This is conducive to improving the conductivity of the second film layer while also taking into account high energy density.

[0035] In some embodiments, the coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 . This is conducive to increasing the number of lithium ions released per unit area of the negative electrode film layer, thereby improving the energy density of the battery.

[0036] In some embodiments, the thickness of the negative electrode film layer disposed on one side of the negative electrode current collector is 40 μm to 75 μm. This is conducive to the negative electrode film layer having high capacity and high lithium ion and electron transport performance, and thus the secondary battery having high energy density and fast charging performance.

[0037] In some embodiments, the compaction density of the negative electrode tab is 1.3 g / cm 3 to 1.85 g / cm. This is conducive to the first film layer maintaining a good pore structure, reducing the tortuosity of the negative electrode tab, shortening the lithium ion transport path, and thus improving the fast charging performance and service life performance of the battery while maintaining high energy density.

[0038] In some embodiments, the thickness of the negative electrode current collector is 4 μm to 8 μm. The thickness of the negative electrode current collector is in the above range, which is conducive to the battery achieving high energy density and reducing the risk of negative electrode current collector cracking, thereby prolonging the service life of the battery.

[0039] In some embodiments, the secondary battery further comprises a positive electrode tab, the positive electrode tab comprising a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, the positive electrode active material comprising a first positive electrode active material, the first positive electrode active material comprising an olivine-structured lithium-containing phosphate. The olivine-structured lithium-containing phosphate has a stable three-dimensional lattice structure, which can remain relatively stable during lithium ion intercalation and deintercalation, and is not prone to structural collapse or deformation, which enables the olivine-structured lithium-containing phosphate to withstand multiple charge and discharge cycles without damage, thereby prolonging the service life of the battery.

[0040] In some embodiments, the olivine-structured lithium-containing phosphate comprises a compound as shown in formula (I): , formula (I); In formula (I), M 1 is selected from at least one of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn, and Pb, 0≤x≤1, 0≤y<1. The above-mentioned lithium-containing phosphate has a stable lattice structure and is not prone to phase transition, which can further improve the service life of the secondary battery.

[0041] In some embodiments, the first positive electrode active material further comprises a positive electrode coating layer, the positive electrode coating layer being disposed on at least part of the surface of the lithium-containing phosphate, and the positive electrode coating layer comprising at least one of a fast ion conductor material and a carbon material.

[0042] The carbon material is in a loose and porous form, which can make the electrolyte and the lithium iron phosphate substrate fully and effectively contact, thereby improving the wetting performance of the electrolyte on the positive electrode film layer, and further improving the fast charging performance of the secondary battery.

[0043] The fast ion conductor material has high ionic conductivity, and the selection of the positive electrode coating layer containing the fast ion conductor material is beneficial to improving the fast charging performance of the battery.

[0044] In some embodiments, in the positive electrode coating layer, the mass ratio of the fast ion conductor material and the carbon material is (0-100):(100-0). By controlling the mass ratio of the fast ion conductor material and the carbon material in the above range, the fast charging performance of the battery is improved.

[0045] In some embodiments, the positive electrode coating layer includes a first coating layer and a second coating layer; the first coating layer includes the fast ion conductor material, and the second coating layer includes the carbon material; the first coating layer is arranged between the lithium-containing phosphate and the second coating layer; the carbon material generally has good adhesion, and the arrangement of the second coating layer containing the carbon material on the outer surface of the first positive electrode active material in this embodiment is beneficial to enhancing the adhesion between the first positive electrode active material and the current collector, reducing the risk of the first positive electrode active material falling off during the use of the battery, and improving the service life of the battery.

[0046] In some embodiments, the positive electrode coating layer includes a first coating layer and a second coating layer; the first coating layer includes the fast ion conductor material, and the second coating layer includes the carbon material, and the second coating layer is arranged between the lithium-containing phosphate and the first coating layer. In this embodiment, lithium ions first pass through the first coating layer composed of the fast ion conductor material during conduction, then enter the second coating layer, and finally diffuse into the lithium-containing phosphate, thereby facilitating the migration speed of lithium ions in the first positive electrode active material, and improving the fast charging performance of the battery. In addition, the carbon material of the second coating layer has good electrical conductivity, which can form a continuous conductive network between the lithium-containing phosphate and the first coating layer to accelerate the transmission of electron conduction, thereby further improving the fast charging performance of the battery.

[0047] In some embodiments, the fast ion conductor material includes a compound as shown in formula (II): Formula (II); in formula (II), M 2 at least one selected from Ti, Zr, Hf, Ge, and Sn, and 0≤b≤1. The above fast ion conductor material has excellent ionic conductivity, and the selection of the above fast ion conductor material is beneficial to further improving the fast charging performance of the battery.

[0048] In some embodiments, the mass percentage of carbon elements in the first positive electrode active material is 1% to 1.5%. In this way, on the one hand, it is beneficial for the first positive electrode active material to achieve high capacity, thereby facilitating the secondary battery to achieve high energy density, and on the other hand, it is beneficial to improve the electronic conductivity of the first positive electrode active material, thereby improving the fast charging performance of the lithium ion secondary battery.

[0049] In some embodiments, the BET specific surface area of the first positive electrode active material is 12 m 2 / g to 16 m 2 / g; in this way, the surface of the first positive electrode active material can provide more lithium ion insertion and extraction channels. In the fast charging process, lithium ions can be more quickly inserted into the first positive electrode active material through these channels, reducing the transmission distance and resistance of lithium ions, thereby improving the fast charging performance of the battery.

[0050] In some embodiments, the tap density of the first positive electrode active material is 0.8 g / cm 3 to 1.3 g / cm 3 ; in this way, it is beneficial for the positive electrode film layer to form a rich pore structure, which can ensure that the battery has more excellent fast charging performance.

[0051] In some embodiments, the volume average particle size Dv50 of the first positive electrode active material is 1 μm to 3 μm, thereby facilitating the formation of a rich pore structure between the particles of the first positive electrode active material, improving the lithium ion and electron transmission performance in the positive electrode film layer, and thereby improving the kinetic performance of the secondary battery.

[0052] In some embodiments, the compaction density of the first positive electrode active material under 50,000 N is 2.4 g / cm 3 to 2.6 g / cm 3 . In this way, the first positive electrode material is in closer contact, which is beneficial to improve the energy density of the battery.

[0053] In some embodiments, the positive electrode active material further includes a second positive electrode active material, and the second positive electrode active material includes a lithium transition metal oxide. The lithium transition metal oxide has a higher specific capacity, and by selecting a lithium transition metal oxide as the second positive electrode active material, it is beneficial to further improve the energy density of the secondary battery.

[0054] In some embodiments, the mass ratio of the first positive electrode active material to the second positive electrode active material is (99-90):(1-10). In this way, it is beneficial to balance the service life and energy density of the secondary battery.

[0055] In some embodiments, the thickness of the positive electrode film layer arranged on one side of the positive electrode current collector is 60-130 μm, thereby facilitating the positive electrode film layer to have high capacity, high lithium ion and electron transport performance, and thereby facilitating the secondary battery to have high energy density and fast charging performance.

[0056] In some embodiments, the coating weight of the positive electrode film layer arranged on one side of the positive electrode current collector is 200-400 mg / 1540.25 mm 2 . 2 ; thereby facilitating the number of lithium ions released per unit area of the positive electrode film layer to be increased, and thereby the energy density of the battery to be increased.

[0057] In some embodiments, the compaction density of the positive electrode tab is 2-3 g / cm 3 . 3 ; thereby facilitating the positive electrode tab to have a good pore structure, reducing the tortuosity of the positive electrode film layer, shortening the lithium ion transport path, and thereby improving the fast charging performance and life performance of the battery while having high energy density.

[0058] In some embodiments, the thickness of the positive electrode current collector is 10-18 μm; thereby on the one hand facilitating the battery to have high energy density, and on the other hand facilitating the risk of positive electrode current collector cracking to be reduced, and thereby the service life of the battery to be prolonged.

[0059] In some embodiments, the positive electrode film layer further comprises a positive electrode dispersant, and the positive electrode dispersant comprises at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, and sodium carboxymethyl cellulose. The above-mentioned positive electrode dispersant has good flexibility and elasticity, and can disperse the stress borne by the positive electrode active material during compaction; by selecting the above-mentioned positive electrode dispersant, the positive electrode film layer is facilitated to have high compaction density, and thereby the energy density of the battery is increased.

[0060] In some embodiments, the mass fraction of the positive electrode dispersant relative to the positive electrode film layer is 0.3%-5%; thereby facilitating the battery to have high energy density.

[0061] In some embodiments, the secondary battery further comprises an electrolyte, the electrolyte comprising an electrolyte salt and a solvent; the solvent comprising at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butanedisulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone; the electrolyte salt comprising at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0062] In some embodiments, the electrolyte further comprises an additive, the additive comprising at least one of barium sulfate, polytrifluoroethyl methacrylate, bicyclic sulfate, tricyclic sulfate, tris(trimethylsilyl)phosphate, and vinylene carbonate. The additive is preferentially electrochemically reduced on the surface of the negative electrode plate to form a dense and stable SEI film, thereby facilitating the inhibition of lithium dendrite growth and improving the safety performance of the battery.

[0063] In some embodiments, the mass fraction of the additive in the electrolyte is 1% to 10%. This facilitates the formation of an SEI film with an appropriate thickness on the surface of the electrode, which on the one hand facilitates the inhibition of lithium dendrite growth and improves the safety performance of the battery, and on the other hand facilitates the consideration of the transmission resistance of lithium ions in the negative electrode plate, thereby taking into account the fast charging performance of the battery.

[0064] In some embodiments, the electrolyte has an electrical conductivity of 10 mS / cm to 18.5 mS / cm. This facilitates the reduction of the internal impedance of the battery, thereby reducing the energy loss caused by resistance during charging and discharging.

[0065] In some embodiments, the secondary battery further comprises a separator film, the separator film comprising a base film, the thickness of the base film being 3 μm to 18 μm. This on the one hand facilitates the realization of high energy density of the secondary battery, and on the other hand facilitates the reduction of the volume shrinkage rate of the base film at high temperature, facilitates the maintenance of the stability and integrity of the structure of the base film at high temperature, reduces the risk of short circuit between the positive and negative electrodes, and improves the safety performance of the battery.

[0066] In some embodiments, the separator film further comprises a coating layer disposed on at least one side of the base film, the coating layer comprising heat-resistant particles interwoven to form a porous structure. In this embodiment, the heat-resistant particles are interwoven to form a porous structure, which is advantageous in reducing the obstruction of the coating layer to ion transport, thereby improving the efficiency of ion transport. In addition, the coating layer comprises heat-resistant particles, the volume of which changes little with temperature, and disposing the coating layer comprising heat-resistant particles on the surface of the base film is advantageous in inhibiting the thermal shrinkage of the base film, thereby further reducing the risk of short circuit of the positive and negative electrodes and improving the safety performance of the battery.

[0067] The second aspect of the present application also provides a power consuming device comprising the secondary battery of the first aspect of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; Figure 2 is an exploded view of the secondary battery according to an embodiment of the present application shown in Figure 1 Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application; Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application; Figure 5 is an exploded view of the battery pack according to an embodiment of the present application shown in Figure 4 Figure 6 is a schematic diagram of a power consuming device using the secondary battery according to an embodiment of the present application as a power source; Figure 7 is a cross-sectional SEM photograph of a negative electrode sheet prepared for Example 1; Figure 8 is a cross-sectional SEM photograph of a second film layer in a negative electrode sheet prepared for Example 2.

[0069] REFERENCE SIGNS: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 battery cell; 51 case; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0070] Hereinafter, embodiments of the secondary battery and the power consuming device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed description is omitted. For example, there can be cases where detailed description of matters well known to those skilled in the art, repeated description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the present application thereto. ​​The ranges disclosed herein are intended to be "open" ranges, i.e., the upper and lower limits of the range are not included. The ranges can be "closed" ranges, i.e., the upper and lower limits of the range are included. The ranges can be any combination of open and closed ranges. For example, if a range of 60-120 and 80-110 is listed, it is understood that a range of 60-110 and 80-120 is also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise indicated, a numerical range "a-b" means a range of any combination of the numbers a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand for listing all of those numbers. Also, when a parameter is stated to be an integer > 2, it is equivalent to state that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0071] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0072] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0073] All steps of the present application can be performed in sequence or randomly, preferably in sequence, unless otherwise specified. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0074] Unless otherwise specified, "including" and "comprising" mentioned in the present application means open-ended, and can also be closed-ended. For example, "including" and "comprising" can mean that other components not listed can also be included or contained, or only the listed components can be included or contained.

[0075] The graphite material has a stable layered structure. During the process of lithium ion insertion and extraction, the layered structure can maintain relative stability and is not prone to obvious structural changes or collapse, which allows the battery to maintain good performance after multiple charge and discharge cycles and prolongs the service life of the battery. Therefore, graphite material has become the mainstream negative active material.

[0076] With the continuous development of secondary batteries in various fields, the market has higher requirements for secondary batteries, such as requiring secondary batteries to have both fast charging performance and long service life.

[0077] However, the lithium ion diffusion rate of graphite material has limitations. When the charging current is too large (i.e., fast charging), the speed of lithium ion insertion into the graphite layer cannot keep up with the external applied charging speed, causing lithium ions to be precipitated on the surface of the graphite negative electrode. The precipitation of lithium ions directly causes the number of lithium ions that can participate in the charge and discharge cycle inside the battery to decrease. Because some of the precipitated lithium ions may not be able to normally deintercalate back into the electrolyte to participate in the cycle, these lithium ions are equivalent to "losing activity" and cannot function for the charge and discharge functions of the battery. The decrease in the number of lithium ions will directly cause the battery capacity to decrease, and as the number of charge and discharge cycles increases, the battery capacity will decay more severely, ultimately affecting the service life of the battery.

[0078] How to balance the fast charging performance and service life of the battery has become a technical problem to be solved.

[0079] To solve the above technical problems, the present application provides a secondary battery and a power consumption device. The secondary battery balances the fast charging performance and service life.

[0080] The first aspect of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer located on at least one surface of the negative electrode current collector, the negative electrode film layer comprising a first film layer and a second film layer arranged between the first film layer and the negative electrode current collector, the first film layer comprising a first negative active material, the first negative active material comprising a first graphite material, the I D / I G of the first graphite material is 0.5 to 0.9; the second film layer comprises a second negative active material, the second negative active material comprising a second graphite material, the I D / I G of the second graphite material is 0.05 to 0.2; wherein I D represents the D peak intensity of the Raman spectrum at 1350±50 cm -1 ; I G represents the G peak intensity of the Raman spectrum at 1580±50 cm -1 .

[0081] The ID / I G 0.5 to 0.9, indicating that there are a large number of defects on the surface of the first graphite material, which can serve as additional active sites for lithium ion intercalation. By arranging the first graphite material with more surface defects on the outer layer (first film layer) of the negative electrode sheet, the contact probability of the additional active sites with the electrolyte can be increased, thereby improving the fast charging performance of the battery.

[0082] On this basis, the inner layer (second film layer) of the negative electrode sheet uses a second graphite material with I D / I G 0.05 to 0.2, which has fewer surface defects and a relatively complete structure, which is conducive to reducing the irreversible loss of lithium ions, thereby prolonging the service life of the battery.

[0083] In this application, the morphology of the negative electrode sheet can be tested by methods known in the art. The negative electrode sheet to be tested can be a prepared negative electrode sheet, or a negative electrode sheet obtained by disassembling a battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the negative electrode sheet is obtained by disassembling the battery, locked and fixed on the sample holder, the cross section of the negative electrode sheet is cut by an argon ion section polisher (for example, the IB-09010 CP argon ion section polisher of Japan JEOL Company), and the SEM photo of the cross section of the negative electrode sheet is collected by a scanning electron microscope (HR-TEM Talos F200). From the cross-sectional SEM photo, it can be known that the negative electrode sheet includes a negative electrode current collector, a second film layer arranged on the surface of the negative electrode current collector, and a first film layer arranged on the surface of the second film layer.

[0084] In this application, the I D / I G value of the graphite material (first graphite material, second graphite material) can be tested by methods known in the art. The graphite material to be tested can be a prepared graphite material, or a graphite material obtained by disassembling a battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the negative electrode sheet is obtained by disassembling the battery, the first film layer can be scraped off by a scraper, or scraped off by an instrument, dissolved in an appropriate solvent, and then the first graphite material is filtered out, and the I D / I G .

[0085] The second film layer is scraped off by a scraper, dissolved in an appropriate solvent, and then the second graphite material is filtered out, and the I D / I GIt is to be noted that there can be an obvious interface at the junction of the first film layer and the second film layer in the negative electrode film layer, or there can be no obvious interface. In order to reduce sampling error, the sampling area of the second film layer is 2.5 μm from the surface of the negative electrode film layer close to the current collector to the direction of the negative electrode film layer; the sampling area of the first film layer is 2.5 μm from the surface of the negative electrode film layer away from the current collector to the direction of the negative electrode film layer.

[0086] As an example, the test conditions are: excitation wavelength is 532 nm, grating is 600 lines, objective lens is 50 times, integration time is 10 s, cumulative number is 3 times, surface scanning, 100 points of D peak and G peak intensity are obtained, and 100 points of I D / I G , remove the maximum and minimum 30 I D / I G , and the average value of the remaining 40 points is the I D / I G of the material. The test instrument can use Horiba LabRAM HR800 Raman spectrometer.

[0087] In the present application, the I D / I G of the first graphite material is 0.5 to 0.9. As an example, the I D / I G of the first graphite material is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or a value between any two of the ranges, but not limited thereto.

[0088] In the present application, the I D / I G of the second graphite material is 0.05 to 0.2. As an example, the I D / I G of the second graphite material is 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2 or a value between any two of the ranges, but not limited thereto.

[0089] In some embodiments, the electrode assembly is a wound electrode assembly. Thereby it is advantageous to improve the energy density of the secondary battery.

[0090] The term "secondary battery" referred to herein refers to a battery cell, a battery module or a battery pack. The following are described respectively. The battery referred to in the present application refers to a secondary battery, unless otherwise specified.

[0091] Generally, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, lithium ions are intercalated and deintercalated between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and functions to prevent short circuiting between the positive electrode and the negative electrode while allowing ions to pass through.

[0092] Negative electrode sheet The negative electrode sheet includes a negative current collector and a negative film layer disposed on at least one surface of the negative current collector. The negative film layer includes a first film layer and a second film layer disposed between the first film layer and the negative current collector. The first film layer includes a first negative active material including a first graphite material. The second film layer includes a second negative active material including a second graphite material.

[0093] As an example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative film layer is disposed on either one or both of the two opposite surfaces of the negative current collector.

[0094] In some embodiments, the first graphite material has a volume average particle size of 9.2 μm to 15.5 μm. This is advantageous for forming abundant pore structures between the particles of the first graphite material, thereby improving the lithium ion and electron transport properties in the first film layer, and further improving the kinetic properties of the secondary battery. Illustratively, the first graphite material has a volume average particle size Dv50 of 9.2 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 15.5 μm, or a value between any two of these values, but is not limited thereto.

[0095] In some embodiments, the second graphite material has a volume average particle size Dv50 of 16.3 μm to 25.5 μm. This is advantageous for improving the compaction density of the second film layer, thereby improving the energy density of the secondary battery. In addition, this is also advantageous for forming abundant pore structures between the particles of the second graphite material, improving the lithium ion and electron transport properties in the negative film layer, and further improving the kinetic properties of the secondary battery. Illustratively, the second graphite material has a volume average particle size Dv50 of 16.3 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25.5 μm, or a value between any two of these values, but is not limited thereto.

[0096] In the present application, the volume distribution particle size Dv50 of the material represents the particle size corresponding to the cumulative volume distribution percentage of 50%, which can be determined by using instruments and methods known in the art. For example, GB / T 19077-2016 can be referred to, and a laser particle size analyzer can be used for determination. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0097] In some embodiments, the BET specific surface area of the first graphite material is 0.3m 2 / g to 3m 2 / g. When the BET specific surface area of the first graphite material is within the above range, the surface of the first graphite material can provide more channels for lithium ion intercalation and deintercalation. During fast charging, lithium ions can intercalate into the first graphite material more quickly through these channels, reducing the transmission distance and resistance of lithium ions, thereby improving the fast charging performance of the battery. Exemplarily, the BET specific surface area of the first graphite material is 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g, 3m 2 / g or any range formed by any two of the numerical values, but the present application is not limited thereto.

[0098] In some embodiments, the BET specific surface area of the second graphite material is 0.5m 2 / g to 5m 2 / g. When the BET specific surface area of the second graphite material is within the above range, the surface of the second graphite material can provide more channels for lithium ion intercalation and deintercalation. During fast charging, lithium ions can intercalate into the second graphite material more quickly through these channels, reducing the transmission distance and resistance of lithium ions, thereby improving the fast charging performance of the battery. Exemplarily, the BET specific surface area of the second graphite material is 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m2 / g, 3m 2 / g, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 5m 2 / g, or any two values within the range, but not limited to.

[0099] In the present application, the specific surface area BET of the material (the second graphite material, the first graphite material, the first positive electrode active material) is the meaning known in the art, which can be measured by the instruments and methods known in the art. For example, it can be tested by the nitrogen adsorption specific surface area analysis test method according to GB / T 19587-2017, and calculated by the BET (Brunauer Emmett Teller) method. The test instrument can be a Tri-Star 3020 type specific surface area pore size analysis tester of Micromeritics Company in the United States.

[0100] In some embodiments, the tap density of the first graphite material is 0.7g / cm 3 to 1.6g / cm 3 . The tap density of the first graphite material in the above range is beneficial to the first film layer to form a rich pore structure, which can ensure that the battery has more excellent fast charging performance. Exemplarily, the tap density of the first graphite material is 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 or any two values within the range, but not limited to.

[0101] In some embodiments, the tap density of the second graphite material is 0.8g / cm 3 to 1.5g / cm 3 . The tap density of the second graphite material in the above range can be tightly packed in the second film layer, which is beneficial to the second film layer to accommodate more second graphite materials (active substances), thereby improving the energy density of the battery. Exemplarily, the tap density of the second graphite material is 0.8g / cm 3 , 0.9g / cm 3 , 1g / cm 3 , 1.1g / cm 31.2 g / cm3 3 1.3 g / cm3 3 1.4 g / cm3 3 1.5 g / cm3 3 or any two of the numerical values define the range, but not limited to.

[0102] In the present application, the tap density of the material (the second graphite material, the first graphite material, the first positive electrode active material) is the meaning known in the art, which can be measured by instruments and methods known in the art. For example, GB / T 5162-2006 can be referred to, and a powder tap density tester can be used for measurement. The testing instrument can use Dandong Bit BT-301, and the test parameters are as follows: vibration frequency 250±15 times / min, vibration amplitude 3±0.2 mm, vibration times 5000 times, and cylinder 25 mL.

[0103] In some embodiments, the first negative electrode active material further comprises a negative electrode coating layer distributed on the surface of the first graphite material, and the negative electrode coating layer comprises amorphous carbon. The structure of amorphous carbon is relatively loose, and has a rich pore structure. These pores can provide more diffusion channels for lithium ions, shorten the diffusion path of lithium ions in the electrode material, and set the amorphous carbon on the surface of the first graphite material. Lithium ions can pass through the negative electrode coating layer to the inside of the first graphite material more quickly, thereby improving the fast charging performance of the battery.

[0104] In the present application, TEM can be used to characterize the negative electrode coating layer on the surface of the first graphite material. SEM is used to collect the micro-morphology information of the first negative electrode active material. The first graphite material is observed by TEM to have a periodic repeating lattice structure. If no regular lattice structure is found on the surface of the first graphite material, it indicates that amorphous carbon is provided on the surface of the first graphite material.

[0105] In some embodiments, the thickness of the negative electrode coating layer is 10 nm to 100 nm. The thickness of the negative electrode coating layer in the above range is beneficial to the fast charging performance and energy density of the secondary battery. Exemplarily, the thickness of the negative electrode coating layer is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or a value between any two of the numerical values define the range, but not limited to.

[0106] In the present application, scanning electron microscope (SEM) combined with focused ion beam (FIB) can be used to characterize the thickness of the negative electrode coating layer. The sample (the first negative electrode active material) is fixed on the sample stage, and a flat cross section is cut on the surface of the sample by FIB. Then SEM is used to image the cross section, and the thickness of the negative electrode coating layer is determined by measuring the width of the negative electrode coating layer in the image.

[0107] In some embodiments, the second film layer further comprises a first graphite material. The second graphite material can reduce the irreversible loss of active lithium ions in multiple charge-discharge cycles, reduce the decay rate of battery capacity, and prolong the service life of the battery. The first graphite material can improve the fast-charging performance of the battery. In this embodiment, by arranging the second graphite material and the first graphite material in the second film layer, the fast-charging performance and the service life of the battery can be improved.

[0108] In the present application, the second film layer contains the second graphite material and the first graphite material, which can be tested by methods known in the art. The negative electrode sheet to be tested can be prepared or obtained by disassembling the battery. Specifically, the negative electrode sheet is locked and fixed on the sample holder, the cross section of the negative electrode sheet is cut by an argon ion cross-section polisher (for example, IB-09010 CP argon ion cross-section polisher of Japan JEOL Co., Ltd.), and the SEM photo of the cross section of the negative electrode sheet is collected by a scanning electron microscope (HR-TEM Talos F200). From the cross-sectional SEM photo, it can be seen that the negative electrode sheet includes a negative current collector, a second film layer arranged on the surface of the negative current collector, and a first film layer arranged on the surface of the second film layer. The second film layer contains large particle materials and small particle materials. The large particle materials are the second graphite material, and the small particle materials are the first graphite material.

[0109] In some embodiments, the mass ratio of the second graphite material to the first graphite material in the second film layer is (3-5):(5-7). By controlling the mass ratio of the second graphite material to the first graphite material in the second film layer within the above range, the fast-charging performance and the service life of the battery can be further improved. Exemplarily, the mass ratio of the second graphite material to the first graphite material in the second film layer is 5:5, 4:6, 3:7, or a value between any two values, but is not limited thereto.

[0110] In the present application, the mass ratio of the second graphite material to the first graphite material in the second film layer can be tested by methods known in the art. The negative electrode sheet to be tested can be prepared or obtained by disassembling the battery. Specifically, the negative electrode sheet is obtained by disassembling the battery, and the first film layer is removed by a scraper to expose the second film layer. The second film layer is removed by a scraper, and the second film layer is collected. The second film layer is dissolved with a suitable solvent, and the mixture of the second graphite material and the first graphite material is obtained by filtration. The second graphite material and the first graphite material are separated by the difference in particle size (the particle size of the second graphite material is larger than that of the first graphite material), and the mass of the second graphite material and the mass of the first graphite material are weighed, respectively, to obtain the mass ratio of the second graphite material to the first graphite material in the second film layer.

[0111] In some embodiments, the ratio of the average thickness of the first film layer to the average thickness of the second film layer is (3-5):(5-7). By controlling the ratio of the average thickness of the first film layer to the average thickness of the second film layer within the above range, it is beneficial to further balance the improvement of the fast-charging performance and the service life of the battery. Illustratively, the ratio of the average thickness of the first film layer to the average thickness of the second film layer is 5:5, 4:6, 3:7 or a value between any two values within the range, but is not limited thereto.

[0112] In the present application, the ratio of the average thickness of the first film layer to the average thickness of the second film layer can be tested by methods known in the art. The negative electrode sheet to be tested can be a prepared negative electrode sheet or a negative electrode sheet obtained by disassembling a battery. Specifically, a scanning electron microscope (HR-TEM Talos F200) is used to collect a cross-sectional SEM photo of the negative electrode sheet. From the cross-sectional SEM photo, it can be clearly seen that the negative electrode sheet is composed of a negative electrode current collector, a second film layer on the surface of the current collector, and a first film layer on the surface of the second film layer. Subsequently, 4 sampling points are uniformly selected on the first film layer and the second film layer respectively, and the thickness of the film layer at each sampling point is accurately measured using image analysis software. The thickness values of the 4 sampling points of the first film layer are averaged to obtain the average thickness of the first film layer; similarly, the average thickness of the second film layer is obtained. Finally, by calculating the ratio of the average thicknesses of the two, the ratio of the average thickness of the first film layer to the average thickness of the second film layer can be accurately obtained.

[0113] In some embodiments, the first film layer further comprises a first binder, and the first binder comprises at least one of styrene butadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate or carboxymethyl chitosan. The above-mentioned substances have high viscosity, and by selecting the above-mentioned substances as the first binder, the risk of separation of the first film layer from the second film layer can be reduced, thereby being beneficial to further improving the service life of the secondary battery.

[0114] In some embodiments, the first binder comprises at least one of styrene butadiene rubber, lithium polyacrylate and polyacrylate.

[0115] Styrene butadiene rubber has good flexibility and elasticity, and it can disperse the stress borne by the first negative electrode active material during the compaction process, so that the first negative electrode active material can bear greater pressure. By selecting styrene butadiene rubber as the first dispersant, it is beneficial to achieve high compaction density of the first film layer, thereby improving the energy density of the battery.

[0116] Lithium polyacrylate has high ionic conductivity, and by selecting it as the first binder, it is beneficial to improve the fast-charging performance of the battery.

[0117] The polyacrylate can improve the compression modulus of the first negative electrode active material, reduce the adverse effect on the negative electrode sheet dynamics during compression, and thus improve the fast charging performance of the battery.

[0118] In some embodiments, the second film layer further comprises a second binder, and the second binder comprises at least one of styrene butadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, or carboxymethyl chitosan. The viscosity of the above-mentioned second binder is high, and by selecting the above-mentioned substances as the second binder, the risk of the second film layer separating from the negative current collector can be reduced, thereby further improving the service life of the secondary battery.

[0119] In some embodiments, the second binder comprises at least one of styrene butadiene rubber, lithium polyacrylate, and polyacrylate. In this embodiment, by selecting the above-mentioned substances as the second binder, the fast charging performance, service life, and energy density of the battery can be considered.

[0120] In some embodiments, the mass fraction of the first binder in the first film layer is 0.1% to 2%. By controlling the mass fraction of the first binder in the first film layer within the above range, on the one hand, the pulverization and shedding of the first negative electrode active material can be prevented, thereby prolonging the service life of the battery. On the other hand, the battery can achieve high energy density. Exemplarily, the mass fraction of the first binder in the first film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, or a value between any two of the above values.

[0121] In some embodiments, the mass fraction of the second binder in the second film layer is 0.1% to 2%. By controlling the mass fraction of the second binder in the second film layer within the above range, on the one hand, the pulverization and shedding of the second negative electrode active material can be prevented, thereby prolonging the service life of the battery. On the other hand, the battery can achieve high energy density. Exemplarily, the mass fraction of the second binder in the second film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, or a value between any two of the above values.

[0122] In some embodiments, the first film layer further comprises a first dispersant, and the first dispersant comprises at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0123] The above-mentioned substances have high ionic conductivity, and by selecting them as the first dispersant, the fast charging performance of the battery can be improved.

[0124] In some embodiments, the second film layer further comprises a second dispersant, and the second dispersant comprises at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose. The above-mentioned substances have high ionic conductivity, and by selecting them as the second dispersant, the fast-charging performance of the battery can be improved.

[0125] In some embodiments, the first dispersant comprises lithium carboxymethyl cellulose. Lithium carboxymethyl cellulose contains lithium ions, so that the loss of active lithium ions caused by the formation of an SEI film during the first charging can be compensated for, thereby improving the first charging efficiency of the battery.

[0126] In some embodiments, the second dispersant comprises lithium carboxymethyl cellulose. Lithium carboxymethyl cellulose contains lithium ions, so that the loss of active lithium ions caused by the formation of an SEI film during the first charging can be compensated for, thereby improving the first charging efficiency of the battery.

[0127] In some embodiments, the mass percentage of the first dispersant in the first film layer is 0.3% to 1.5%. By controlling the mass percentage of the first dispersant in the first film layer within the above range, the battery can achieve a high energy density. For example, the mass percentage of the first dispersant is 0.3%, 0.5%, 1%, 1.5%, or a value within the range between any two of the above values.

[0128] In some embodiments, the mass percentage of the second dispersant in the second film layer is 0.3% to 1.5%. By controlling the mass percentage of the second dispersant in the second film layer within the above range, the battery can achieve a high energy density. For example, the mass percentage of the second dispersant is 0.3%, 0.5%, 1%, 1.5%, or a value within the range between any two of the above values.

[0129] In some embodiments, the first film layer further comprises a first conductive agent, and the first conductive agent comprises at least one of super conductive carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black. The above-mentioned substances have good conductivity, and by using them as the first conductive agent, the fast-charging performance of the battery can be further improved. Alternatively, the first conductive agent comprises carbon nanotubes and conductive carbon black, and by using them as the first conductive agent, the fast-charging performance of the battery can be further improved.

[0130] In some embodiments, the second film layer further comprises a second conductive agent, and the second conductive agent comprises at least one of super conductive carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black. The above-mentioned substances have good conductivity, and by using them as the second conductive agent, the fast-charging performance of the battery can be further improved. Alternatively, the second conductive agent comprises carbon nanotubes and conductive carbon black.

[0131] In some embodiments, the mass percentage of the first conductive agent in the first film layer is 0.1% to 2%. By controlling the mass percentage of the first conductive agent in the first film layer in the above range, the overall conductivity of the first film layer is improved, thereby further improving the fast charging performance of the secondary battery. Illustratively, the mass percentage of the first conductive agent in the first film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, or a value between any two of the above values.

[0132] In some embodiments, the mass percentage of the second conductive agent in the second film layer is 0.1% to 2%. By controlling the mass percentage of the second conductive agent in the second film layer in the above range, the overall conductivity of the second film layer is improved, thereby further improving the fast charging performance of the secondary battery. Illustratively, the mass percentage of the second conductive agent in the second film layer is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, or a value between any two of the above values.

[0133] In some embodiments, the thickness of the negative electrode film layer disposed on one side of the negative electrode current collector is 40 μm to 75 μm. By controlling the thickness of the negative electrode film layer in the above range, the negative electrode film layer has high capacity and high lithium ion and electron transport performance, thereby the secondary battery has high energy density and fast charging performance. Illustratively, the thickness of the negative electrode film layer can be 40 μm, 50 μm, 60 μm, 70 μm, 75 μm, or a value between any two of the above values. Alternatively, the thickness of the negative electrode film layer is 45 μm to 55 μm.

[0134] In some embodiments, the coating weight of the negative electrode film layer disposed on one side of the negative electrode current collector is 80 mg / 1540.25 mm 2 to 170 mg / 1540.25 mm 2 . By controlling the coating weight of the negative electrode film layer in the above range, the number of lithium ions released per unit area of the negative electrode film layer is increased, thereby the energy density of the battery is improved. Illustratively, the coating weight of the negative electrode film layer is 80 mg / 1540.25 mm 2 , 90 mg / 1540.25 mm 2 , 100 mg / 1540.25 mm 2 , 110 mg / 1540.25 mm 2 , 120 mg / 1540.25 mm 2 , 130 mg / 1540.25 mm 2 , 140 mg / 1540.25 mm 2 , 150 mg / 1540.25 mm 2, 160 mg / 1540.25 mm 2 , 170 mg / 1540.25 mm 2 or a value between any two of the recited values. Optionally 110 mg / 1540.25 mm 2 to 140 mg / 1540.25 mm 2 .

[0135] In the present application, the coating weight of the negative electrode film layer can be tested by methods known in the art. The negative electrode tab to be tested can be a prepared negative electrode tab, or a negative electrode tab obtained by disassembling a battery. Specifically, the negative electrode tab is obtained by disassembling a battery, the negative electrode tab layer is cut into a circular piece with an area of 1540.25 mm 2 , the mass of the circular piece is weighed as m1, then the negative electrode film layer disposed on one side of the circular piece is removed, the mass of the circular piece is weighed as m2, and m1-m2 is taken as the coating weight of the negative electrode film layer.

[0136] In some embodiments, the compaction density of the negative electrode tab is 1.3 g / cm 3 to 1.85 g / cm 3 . By making the compaction density of the negative electrode tab in the above range, the negative electrode tab can maintain a good pore structure, reduce the tortuosity of the negative electrode tab, shorten the lithium ion transmission path, thereby improving the fast charging performance and life performance of the battery, while taking into account the high energy density. Illustratively, the compaction density of the negative electrode tab can be 1.3 g / cm 3 , 1.4 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.60 g / cm 3 , 1.62 g / cm 3 , 1.64 g / cm 3 , 1.65 g / cm 3 , 1.85 g / cm 3 or a value between any two of the recited values. Optionally 1.5 g / cm 3 to 1.75 g / cm 3 .

[0137] In some embodiments, the thickness of the negative current collector is 4 μm to 8 μm. The thickness of the negative current collector is in the above range, on the one hand, it is conducive to the battery to achieve high energy density, on the other hand, it is conducive to reduce the risk of negative current collector cracking, thereby prolonging the service life of the battery. Illustratively, the thickness of the negative current collector is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm or a value between any two of them, optionally, the thickness of the negative current collector is 4.5 μm to 5 μm.

[0138] In some embodiments, the negative current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, a copper foil can be adopted. The composite current collector can include a high polymer material base layer and a metal layer formed on at least one surface of the high polymer material base material. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a high polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0139] In some embodiments, the negative film layer can also optionally include other auxiliary agents, such as thickening agents (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0140] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative current collector, and after drying, cold pressing and the like processes, the negative electrode sheet can be obtained.

[0141] Positive electrode sheet In some embodiments, the positive electrode sheet includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector, and the positive film layer includes a positive electrode active material, and the positive electrode active material includes a first positive electrode active material, and the first positive electrode active material includes an olivine-structured lithium-containing phosphate. The olivine-structured lithium-containing phosphate has a stable three-dimensional lattice structure, which can remain relatively stable during the process of lithium ion insertion and extraction, and is not prone to structural collapse or deformation, which enables the olivine-structured lithium-containing phosphate to withstand multiple charge and discharge cycles without damage, thereby prolonging the service life of the battery.

[0142] In the present application, examples of the lithium-containing phosphate with olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also can be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0143] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction of the positive electrode current collector, and the positive electrode film layer is arranged on either one or both of the two opposite surfaces of the positive electrode current collector.

[0144] In some embodiments, the lithium-containing phosphate with olivine structure comprises a compound as shown in formula (I): , formula (I); in formula (I), M 1 is selected from at least one of V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn and Pb, 0≤x≤1, 0≤y<1. The above-mentioned lithium-containing phosphate has a stable crystal lattice structure and is not prone to phase change, thereby further improving the service life of the secondary battery. Exemplarily, x is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a value between any two of them. Exemplarily, y is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a value between any two of them.

[0145] In some embodiments, the first positive electrode active material further comprises a positive electrode coating layer arranged on at least part of the surface of the lithium-containing phosphate, and the positive electrode coating layer comprises at least one of a fast ion conductor material and a carbon material. The carbon material is in a loose and porous form, which can enable the electrolyte and the lithium iron phosphate matrix to be in full and effective contact, thereby improving the wettability of the electrolyte to the positive electrode film layer and further improving the fast charging performance of the secondary battery. The fast ion conductor material has high ionic conductivity, and the use of the positive electrode coating layer comprising the fast ion conductor material is conducive to improving the fast charging performance of the battery.

[0146] In some embodiments, the lithium-containing phosphate is provided with a positive electrode coating layer on the surface, and the positive electrode film layer comprises a fast ion conductor material and a carbon material.

[0147] In some embodiments, the positive electrode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a fast ion conductor material, and the second coating layer comprises a carbon material; the first coating layer is arranged between the lithium-containing phosphate and the second coating layer. The carbon material generally has good adhesion, and arranging the second coating layer comprising the carbon material on the outer surface of the first positive electrode active material in this embodiment is beneficial to enhancing the adhesion between the first positive electrode active material and the current collector, reducing the risk of the first positive electrode active material falling off during use of the battery, and improving the service life of the battery.

[0148] In some embodiments, the positive electrode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a fast ion conductor material, and the second coating layer comprises a carbon material; the second coating layer is arranged between the lithium-containing phosphate and the first coating layer.

[0149] In this embodiment, lithium ions first pass through the first coating layer composed of the fast ion conductor material during conduction, then enter the second coating layer, and finally diffuse into the lithium-containing phosphate, thereby facilitating the acceleration of the migration speed of lithium ions in the first positive electrode active material and improving the fast charging performance of the battery. In addition, the carbon material of the second coating layer has good electrical conductivity, which can form a continuous conductive network between the lithium-containing phosphate and the first coating layer to accelerate the transmission of electron conduction, thereby further improving the fast charging performance of the battery.

[0150] In some embodiments, in the positive electrode coating layer, the mass ratio of the fast ion conductor material to the carbon material is (0-100):(100-0). By controlling the mass ratio of the fast ion conductor material to the carbon material in the above range, the fast charging performance of the battery is improved. Exemplarily, the mass ratio of the fast ion conductor material to the carbon material is 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, or a value between any two of them.

[0151] In some embodiments, the fast ion conductor material comprises a compound as shown in formula (II): Formula (II); In formula (II), M 2 is at least one selected from Ti, Zr, Hf, Ge, and Sn, and 0≤b≤1. The above fast ion conductor material has excellent ionic conductivity, and by selecting the above fast ion conductor material, the fast charging performance of the battery is further improved. Exemplarily, b is 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or a value between any two of them.

[0152] In some embodiments, the mass percentage of carbon element in the first positive electrode active material is 1% to 1.5%. By controlling the mass percentage of carbon element in the first positive electrode active material in the above range, on the one hand, it is beneficial for the first positive electrode active material to achieve high capacity, thereby facilitating the secondary battery to achieve high energy density, and on the other hand, it is beneficial to improve the electronic conductivity of the first positive electrode active material, thereby improving the fast charging performance of the lithium ion secondary battery.

[0153] In the present application, the mass percentage of carbon element can be tested by methods known in the art. The positive electrode sheet to be tested can be a prepared positive electrode sheet, or a positive electrode sheet obtained by disassembling a battery. Specifically, the positive electrode sheet is obtained by disassembling a battery, the positive electrode film layer is peeled off from the positive electrode current collector, the positive electrode film layer is collected, and then the positive electrode film layer is dissolved with a suitable solvent, and then the first positive electrode active material is separated out. The mass percentage of carbon element in the first positive electrode active material can be determined by a carbon-sulfur analyzer according to the standard GB / T 20123-2006.

[0154] In some embodiments, the BET specific surface area of the first positive electrode active material is 12 m 2 / g to 16 m 2 / g. When the BET specific surface area of the first positive electrode active material is in the above range, the surface of the first positive electrode active material can provide more lithium ion insertion and extraction channels. During fast charging, lithium ions can be more quickly inserted into the first positive electrode active material through these channels, reducing the transmission distance and resistance of lithium ions, thereby improving the fast charging performance of the battery. For example, the BET specific surface area of the first positive electrode active material is 12 m 2 / g, 12.2 m 2 / g, 12.4 m 2 / g, 12.6 m 2 / g, 12.8 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g, 16 m 2 / g, or any range between any two of the values, but not limited thereto.

[0155] In some embodiments, the tap density of the first positive electrode active material is 0.8 g / cm 3 to 1.3 g / cm 3 . The tap density of the first positive electrode active material in the above range is beneficial for the positive electrode film layer to form a rich pore structure, which can ensure the battery to have more excellent fast charging performance. For example, the tap density of the first positive electrode active material is 0.8 g / cm 3 , 1.1 g / cm 3 , 0.9 g / cm 31.0 g / cm3 3 1.05 g / cm3 3 1.15 g / cm3 3 1.2 g / cm3 3 1.25 g / cm3 3 1.28 g / cm3 3 1.3 g / cm3 3 or any range between any two of the above values, but not limited to.

[0156] In some embodiments, the volume average particle size of the first positive electrode active material is 1 pm to 3 pm. Thereby, it is beneficial to form abundant pore structure among the particles of the first positive electrode active material, to improve the lithium ion and electron transport performance in the positive electrode film layer, and further to improve the kinetic performance of the secondary battery. Illustratively, the volume average particle size Dv50 of the first positive electrode active material is 1 pm, 1.1 pm, 1.2 pm, 1.3 pm, 1.4 pm, 1.5 pm, 1.6 pm, 1.7 pm, 1.8 pm, 1.9 pm, 2 pm, 2.1 pm, 2.2 pm, 2.3 pm, 2.4 pm, 2.5 pm, 2.6 pm, 2.7 pm, 2.8 pm, 2.9 pm, 3 pm, or any range between any two of the above values, but not limited to.

[0157] In some embodiments, the compaction density of the first positive electrode active material under 50000 N is 2.4 g / cm3 3 to 2.6 g / cm3 3 . The compaction density of the first positive electrode active material is in the above range, so that the contact among the first positive electrode materials is closer, which is beneficial to improve the energy density of the battery. Illustratively, the compaction density of the first positive electrode active material is 2.4 g / cm3 3 , 2.5 g / cm3 3 , 2.51 g / cm3 3 , 2.52 g / cm3 3 , 2.53 g / cm3 3 , 2.54 g / cm3 3 , 2.55 g / cm3 3 , 2.56 g / cm3 3 , 2.57 g / cm3 3 , 2.58 g / cm3 3 , 2.59 g / cm3 3 , 2.60 g / cm3 3 , or any range between any two of the above values.

[0158] In some embodiments, the positive electrode active material further comprises a second positive electrode active material, and the second positive electrode active material comprises a lithium transition metal oxide. The lithium transition metal oxide has a higher specific capacity, and by selecting the lithium transition metal oxide as the second positive electrode active material, the energy density of the secondary battery can be further improved.

[0159] In the present application, examples of the lithium transition metal oxide can include, but are not limited to, at least one of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.1 Al 0.05 O2), and modified compounds thereof.

[0160] During the charging and discharging process of the battery, Li will be deintercalated and consumed, and the molar content of Li is different when the battery is discharged to different states. In the present application, the molar content of Li in the list of positive electrode active materials is the initial state of the material, i.e., the state before feeding, and the positive electrode active material is applied to the battery system. After charging and discharging cycles, the molar content of Li will change.

[0161] In the present application, the molar content of oxygen in the list of positive electrode active materials is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will fluctuate.

[0162] In some embodiments, the mass ratio of the first positive electrode active material to the second positive electrode active material is (99-90):(1-10). By controlling the mass ratio of the first positive electrode active material to the second positive electrode active material within the above range, it is beneficial to balance the service life and energy density of the secondary battery. For example, the mass ratio of the first positive electrode active material to the second positive electrode active material is 99:1, 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9, 90:10, or a value within a range of any two of these values.

[0163] In some embodiments, the thickness of the positive electrode film layer disposed on one side of the positive electrode current collector is 60 μm to 130 μm. By keeping the thickness of the positive electrode film layer within the above range, it is beneficial for the positive electrode film layer to achieve both high capacity, high lithium-ion and electron transport performance, thereby benefiting the secondary battery to achieve both high energy density and fast charging performance. For example, the thickness of the positive electrode film layer can be 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, or a value within a range of any two of these values.

[0164] In some embodiments, the coating weight of the positive electrode film layer disposed on one side of the positive electrode current collector is 200 mg / 1540.25 mm. 2 Up to 400mg / 1540.25mm 2 By controlling the coating weight of the positive electrode film within the aforementioned range, the number of lithium ions released per unit area of ​​the positive electrode film can be increased, thereby improving the energy density of the battery. For example, the coating weight of the positive electrode film is 200 mg / 1540.25 mm². 2 220mg / 1540.25mm 2 240mg / 1540.25mm 2 260mg / 1540.25mm 2 280mg / 1540.25mm 2 300mg / 1540.25mm 2 310mg / 1540.25mm 2 320mg / 1540.25mm 2 330mg / 1540.25mm 2 340mg / 1540.25mm 2 350mg / 1540.25mm 2 360mg / 1540.25mm 2 370mg / 1540.25mm 2 380mg / 1540.25mm 2, 390 mg / 1540.25 mm 2 , 400 mg / 1540.25 mm 2 or a value between any two of the recited values. Alternatively, the coating weight of the positive electrode film layer is 250-1540.25 mm 2 to 320 / 1540.25 mm 2 .

[0165] In the present application, the coating weight of the positive electrode film layer can be tested by methods known in the art. The positive electrode tab to be tested can be a prepared positive electrode tab, or a positive electrode tab obtained by disassembling a battery. Specifically, the positive electrode tab is obtained by disassembling a battery, the positive electrode tab is cut into a circular piece with an area of 1540.25 mm 2 , the mass of the circular piece is weighed as m3, then the positive electrode film layer is removed from one side of the circular piece, the mass of the circular piece is weighed as m4, and m3-m4 is taken as the coating weight of the positive electrode film layer.

[0166] In some embodiments, the compaction density of the positive electrode tab is 2 g / cm 3 to 3 g / cm 3 . By making the compaction density of the positive electrode tab in the above range, the positive electrode film layer can maintain a good pore structure, reduce the tortuosity of the positive electrode tab, shorten the lithium ion transmission path, thereby improving the fast charging performance and life performance of the battery, while taking into account the high energy density. Illustratively, the compaction density of the positive electrode tab can be 2 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 , 2.5 g / cm 3 , 2.60 g / cm 3 , 2.7 / cm 3 , 2.8 g / cm 3 , 2.9 g / cm 3 , 3 g / cm 3 or a value between any two of the recited values. Alternatively, the compaction density of the positive electrode tab is 2.3 g / cm 3 to 2.65 g / cm 3 , and further alternatively 2.3 g / cm 3 to 2.5 g / cm 3 .

[0167] In some embodiments, the thickness of the cathode current collector is 10 pm to 18 pm. The thickness of the cathode current collector is in the above range, on the one hand, it is conducive to the battery to achieve high energy density, on the other hand, it is conducive to reducing the risk of cathode current collector cracking, thereby prolonging the service life of the battery. Illustratively, the thickness of the cathode current collector is 10 pm, 11 pm, 12 pm, 13 pm, 14 pm, 14.5 pm, 15 pm, 15.5 pm, 16 pm, 16.5 pm, 17 pm, 17.5 pm, 18 pm or a value between any two of them. Alternatively, the thickness of the cathode current collector is 13 pm to 15 pm.

[0168] In some embodiments, the cathode current collector can adopt a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil can be adopted. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] In some embodiments, the cathode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylic ester resin.

[0170] In some embodiments, the cathode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene or carbon nanofibers.

[0171] In some embodiments, the cathode film layer further includes a cathode dispersant, and the cathode dispersant includes at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, sodium carboxymethyl cellulose. The above-mentioned cathode dispersant has good flexibility and elasticity, can disperse the stress borne by the cathode active material during the compaction process, and by selecting the above-mentioned cathode dispersant, it is conducive to the cathode film layer to achieve high compaction density, thereby improving the energy density of the battery.

[0172] In some embodiments, the mass percentage of the cathode dispersant in the cathode film layer is 0.3% to 5%. Optionally, 0.3% to 1.2%, further optionally 0.5% to 0.8%. By controlling the mass percentage of the cathode dispersant in the cathode film layer within the above range, the battery can achieve a high energy density. Illustratively, the mass percentage of the cathode dispersant is 0.3%, 0.5%, 0.8%, 1%, 1.2%, 2%, 3%, 4%, 5%, or a value between any two of the above values.

[0173] In some embodiments, the cathode electrode sheet can be prepared by dispersing the above-mentioned components for preparing the cathode electrode sheet, such as the cathode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a cathode slurry; coating the cathode slurry on the cathode current collector, and after drying, cold pressing, etc., the cathode electrode sheet can be obtained.

[0174] Electrolyte The electrolyte serves to conduct ions between the cathode electrode sheet and the anode electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or solid.

[0175] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0176] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium boric oxalate, lithium difluorophosphoric oxalate, and lithium tetrafluorophosphoric oxalate.

[0177] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0178] In some embodiments, the electrolyte solution further includes an additive, and the additive includes at least one of barium sulfate, polytrifluoroethyl methacrylate, bicyclic sulfate, tricyclic sulfate, tris(trimethylsilyl)phosphate, and vinylene carbonate. During the first charging and discharging of the battery, the above-mentioned additive will preferentially undergo an electrochemical reduction reaction on the surface of the anode electrode sheet to form a dense and stable SEI film, thereby facilitating the inhibition of lithium dendrite growth and improving the safety performance of the battery.

[0179] In some embodiments, the mass fraction of the additive in the electrolyte is 1% to 10%. By controlling the mass fraction of the additive in the above range, it is beneficial to form a SEI film with moderate thickness on the surface of the electrode, on the one hand, it is beneficial to inhibit the growth of lithium dendrites and improve the safety performance of the battery. On the other hand, it is beneficial to balance the transmission resistance of lithium ions in the negative electrode sheet, thereby balancing the fast charging performance of the battery. Illustratively, the mass fraction of the additive is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a value between any two of them.

[0180] In some embodiments, the conductivity of the electrolyte is 10 mS / cm to 18.5 mS / cm. By selecting an electrolyte with a conductivity in the above range, the internal resistance of the battery can be reduced, and the energy loss due to resistance during charging and discharging can be reduced. Illustratively, the conductivity of the electrolyte is 10 mS / cm, 11 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, 18.5 mS / cm or a value between any two of them. Optionally, the conductivity of the electrolyte is 14 mS / cm to 16.8 mS / cm.

[0181] In some embodiments, the electrolyte can also optionally include an additive. For example, it can include an additive that can improve certain performance of the battery, such as an additive that improves the overcharge performance of the battery, an additive that improves the high-temperature or low-temperature performance of the battery, etc.

[0182] Separation film In some embodiments, the secondary battery further includes a separation film. The type of separation film is not particularly limited in the present application, and any known porous structure separation film with good chemical stability and mechanical stability can be selected.

[0183] In some embodiments, the material of the separation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separation film can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separation film is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0184] In some embodiments, the separator film comprises a base film, and the thickness of the base film is 3-18 μm. The thickness of the base film in the above range indicates that the thickness of the base film is moderate, which is beneficial for the secondary battery to achieve high energy density on the one hand, and beneficial for reducing the volume shrinkage of the base film at high temperature, and beneficial for the base film to maintain its stability and integrity at high temperature, reducing the risk of positive and negative short circuit, and improving the safety performance of the battery. Illustratively, the thickness of the base film is 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm or a value between any two of them. Optionally, the thickness of the base film is 4-15 μm.

[0185] In some embodiments, the base film has nanopores, and the average pore size of the nanopores is 10-300 nm. By using a base film with an average pore size of the nanopores in the above range, it is helpful to improve the migration rate of lithium ions while also taking into account the inhibition of the growth of lithium dendrites, thereby further improving the safety performance of the battery. Illustratively, the average pore size of the nanopores is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 200 nm, 300 nm or a value between any two of them.

[0186] In this application, the average pore size can be tested by methods known in the art. The separator film to be tested can be a prepared separator film or a separator film obtained by disassembling a battery. For example, the separator film (base film) obtained by disassembling the battery can be tested for average pore size using a pore size tester (model: PMI Porometer) according to GB / T21650.2-2008.

[0187] In some embodiments, the porosity of the base film is 20-70%, and by using a base film with a porosity in the above range, it is helpful to improve the migration rate of lithium ions while also taking into account the inhibition of the growth of lithium dendrites, thereby further improving the safety performance of the battery. Illustratively, the porosity of the base film is 20%, 30%, 40%, 50%, 60%, 70% or a value between any two of them. Optionally, the porosity of the base film is 35-42%.

[0188] In the present application, the porosity of the base film can be measured by instruments and methods known in the art. For example, GB / T 24586-2009 can be referred to, and a true density tester can be used for measurement. Specifically: disassemble the battery to obtain the separator film, remove the coating on the surface of the base film, cut the base film into a size of 3 mm x 3 mm, measure the apparent volume V0 of the sample (the apparent volume of the sample is the thickness of the positive electrode film layer x the area of the sample), then use the true density tester to test the true volume of the sample. Specifically, place the sample into the sample test chamber, introduce nitrogen into the sample test chamber, and connect the sample test chamber with the reference chamber and record the stable pressure. By detecting the pressure before the reference chamber is connected with the sample chamber and the stable pressure after the reference chamber is connected with the sample chamber, the volume of the pores is calculated according to the Boyle's law PV = nRT, and the porosity of the sample = pore volume / apparent volume.

[0189] In some embodiments, the separator film further comprises a coating layer disposed on at least one side of the base film, and the coating layer comprises heat-resistant particles interwoven to form a porous structure. Compared with the coating layer without the porous structure, in this embodiment, the heat-resistant particles interwoven to form the porous structure are beneficial to reduce the hindrance of the coating layer to ion transmission, thereby improving the ion transmission efficiency. In addition, the coating layer comprises heat-resistant particles, and the volume of the heat-resistant particles changes little with temperature. Disposing the coating layer comprising heat-resistant particles on the surface of the base film is beneficial to inhibit the thermal shrinkage rate of the base film, thereby further reducing the risk of short circuit of the positive and negative electrodes and improving the safety performance of the battery.

[0190] In some embodiments, the thickness of the coating layer disposed on one side of the base film is 0.01 μm to 2 μm. By selecting a coating layer with a thickness in the above range, on the one hand, it is beneficial to enable the battery to achieve high energy density, and on the other hand, it is beneficial to enable the coating layer to better inhibit the thermal shrinkage rate of the base film, thereby further improving the safety performance of the battery. Illustratively, the thickness of the coating layer is 0.01 μm, 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, or a value between any two of them.

[0191] The test method for the thickness of each layer in the separator film is as follows: cut the separator film along the thickness direction to expose the section, and then use a scanning electron microscope to observe the section of the separator film in the thickness direction. Adjust the electron microscope to an appropriate magnification so that the base film and the coating layer contained in the separator film can be completely observed. The central part is the base film, and the coating layer is disposed on both sides of the base film. Then measure the thickness T1 of the base film single-side coating layer and the thickness t1 of the base film. According to the above operation steps, the thickness T1, T2, T3, T4, T5 of the ceramic layer in 5 different fields of view is tested; and the average value is the thickness of the ceramic layer.

[0192] The thickness values t1, t2, t3, t4, t5 of the base film in 5 different fields of view are tested, and the average value is the thickness of the base film.

[0193] In some embodiments, the average particle size of the heat-resistant particles is 5 nm to 100 nm. The heat-resistant particles with an average particle size of 5 nm to 100 nm can form a stable support network structure coating, supporting the base film while inhibiting thermal shrinkage of the base film, thereby improving the safety performance of the battery. Illustratively, the average particle size of the heat-resistant particles is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a value between any two of them.

[0194] In the present application, the term "particle" refers to a particle in the field of view of the separator film under a certain magnification, for example 10 thousand times, which has a recognizable complete boundary. There can be defects, scratches inside the particle, but the complete boundary inside the particle cannot be recognized enough to divide the particle.

[0195] The identification method of the particles is as follows: the isolation film is cut along the thickness direction by argon ion beam, and the section is observed by scanning electron microscope after exposure. The image is collected by secondary electron mode at a magnification of 10k times under field emission scanning electron microscope, and the particles in the electron microscope image are analyzed by ImageJ software (1.46r, win64 version). The use method of ImageJ software is as follows: load the scanning electron microscope image to be analyzed; identify the particles by using the Cellpose plug-in software, and manually correct on this basis; read and count the data by using Image J. The specific method of identifying particles by using the Cellpose plug-in software is as follows: set the segmentation diameter parameter (diameter in Segmantation module) to 15 pixels, click “run cyto3” to identify particles; manually identify the particles in the image that are not identified by the software or not completely identified by the software or have errors in identification. The particles that are not identified by the software or not completely identified by the software or have errors in identification mainly include the following: 1, the particles are too large or the surface of the particles has scratches, which leads to the failure of identification or complete identification; 2, during the cutting process of argon ion beam, scratches will be generated on the surface of the particles, and the software may misjudge the scratches as the boundary of the particles, thereby causing identification errors; 3, the particles are too small and are not successfully identified; 4, the particles are located at the edge of the electron microscope field, the inside of the particles is penetrated by the edge, the morphology cannot be completely displayed, and the local instead of the whole is identified, which leads to identification errors. The particles that are not identified or have identification errors are manually calibrated, and the specific process is as follows: delete the particles located at the edge of the scanning electron microscope and not completely displayed; judge whether there are cracks in the inside of the particles that are not identified or have identification errors, if there are no cracks in the inside of the particles, it is judged that the particles are one particle, and the particles are manually identified according to the boundary of the particles observed by manual observation; in response to the cracks in the inside of the particles, it is judged whether the cracks penetrate the particles, if the cracks do not penetrate the particles, it is judged that the particles are one particle, and the particles are manually identified; in response to the cracks penetrating the particles, it is judged whether the cracks are linear or irregular; in response to the cracks being irregular, it is judged that the cracks are the boundary between the particles, and the particles are divided along the boundary; in response to the cracks being linear, the contrast is compared; in response to the contrast being not obvious and having no crack feeling, it is judged that the cracks are one particle; in response to the contrast being strong and having crack feeling, it is judged that the cracks are the boundary between the particles, and the cracks are identified as two particles. After manual identification, the information irrelevant to the particles in the image is deleted, that is, the identification and marking of the particles in the image are completed.

[0196] In the present application, the average particle size of the heat-resistant particles can be tested by the following method: In the section of the separator film in the thickness direction, the average particle size of the heat-resistant particles can be tested by the following method: the picture after the particle judgment and identification is imported into the ImageJ software for analysis, the scale setting is completed according to the scanning electron microscope picture, and the particle size of the particles in the section of the negative film layer along the thickness direction of the pole piece is analyzed by the "Feret diameter" analysis function. According to the software manual (ImageJ User Guide IJ1.46r), the "Feret" parameter obtained by analysis represents the maximum distance between all parallel lines in the two-dimensional projection of the particle, which characterizes the particle size of the particle; according to the above method, not less than 10 scanning electron microscope images are collected for each separator film, and the particle size of not less than 5000 particles is counted for each scanning electron microscope image. The average particle size of the particle size of 5000 heat-resistant particles is calculated by the "Feret diameter" of the particles.

[0197] In some embodiments, the particle surface density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 to 2.5 mg / 1540.25 cm 2 . By controlling the particle surface density in the above range, it is beneficial for the battery to achieve energy density while also benefiting the heat-resistant particles to play their role in inhibiting the thermal shrinkage of the base film and improving the safety performance of the battery. Exemplarily, the particle surface density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 , 0.6 mg / 1540.25 cm 2 , 0.7 mg / 1540.25 cm 2 , 0.8 mg / 1540.25 cm 2 , 0.9 mg / 1540.25 cm 2 , 1 mg / 1540.25 cm 2 , 1.1 mg / 1540.25 cm 2 , 1.2 mg / 1540.25 cm 2 , 1.25 mg / 1540.25 cm 2 , 1.3 mg / 1540.25 cm 2 , 1.4 mg / 1540.25 cm 2 , 1.5 mg / 1540.25 cm 2 , 1.6 mg / 1540.25 cm 2 , 1.7 mg / 1540.25 cm 2 , 1.8 mg / 1540.25 cm 2 , 1.85 mg / 1540.25 cm 2or a value between any two of the recited numerical values. Optionally, the particle surface density of the heat-resistant particles is 1.25 mg / 1540.25 cm 2 to 1.85 mg / 1540.25 cm 2 .

[0198] In the present application, the particle surface density of the heat-resistant particles can be tested by methods known in the art. The isolation film to be tested can be a prepared isolation film or an isolation film obtained by disassembling a battery. Specifically, the isolation film is obtained by disassembling a battery, the isolation film is cut into a circular piece with an area of 1540.25 mm 2 The mass of the circular piece is weighed as m6, and then the coating on one side of the circular piece is removed, the mass of the circular piece is weighed as m7, and m 6- m7 is taken as the coating weight of the positive electrode film layer.

[0199] In some embodiments, along the thickness direction of the base film, the heat-resistant particles include first heat-resistant particles, and the first heat-resistant particles are distributed on the surface of the base film. In this embodiment, the first heat-resistant particles are distributed on the surface of the base film, and the first heat-resistant particles can directly inhibit the thermal shrinkage of the base film, thereby further improving the safety performance of the battery, and also taking into account the energy density of the battery.

[0200] In some embodiments, the heat-resistant particles include first heat-resistant particles and second heat-resistant particles; wherein the first heat-resistant particles are distributed on the surface of the base film, and the second heat-resistant particles are stacked on the side of the first heat-resistant particles away from the base film. In this embodiment, the first heat-resistant particles and the second heat-resistant particles are stacked and arranged in the thickness direction of the base film, which is conducive to forming a thicker coating. The thicker coating can serve as a more effective physical barrier to reduce the chemical corrosion of the electrolyte on the base film, and also can buffer the friction of the electrode tab (positive electrode tab, negative electrode tab) on the base film, thereby further improving the safety performance of the battery.

[0201] In some embodiments, the heat-resistant particles include inorganic particles and adhesive particles. In this embodiment, the adhesive particles act as a bridge to tightly connect the inorganic particles together. The inorganic particles form a stable overall structure, thereby improving the mechanical strength and stability of the coating, so that it can better inhibit the thermal shrinkage of the base film.

[0202] In some embodiments, the adhesive particles include one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, or polystyrene acid.

[0203] In some embodiments, the heat-resistant particles include inorganic particles and a bonding layer disposed on at least part of the surface of the inorganic particles. In this embodiment, the bonding layer is disposed on the surface of the inorganic particles, thereby facilitating the improvement of the bonding force between the inorganic particles and the base film, reducing the risk of the inorganic particles falling off, and facilitating the improvement of the safety performance and service life of the battery.

[0204] In some embodiments, the bonding layer includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, or polystyrene acid.

[0205] In some embodiments, the inorganic particles include at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, tin dioxide, boehmite, magnesium oxide, zinc oxide, barium sulfate, magnesium nitride, or barium titanate. The volume of the above-mentioned substances changes little with temperature, and using them as inorganic particles facilitates further inhibition of the thermal shrinkage of the base film, thereby further improving the safety performance of the battery.

[0206] In some embodiments, the mass fraction of the inorganic particles in the coating layer is 5% to 30%. By controlling the mass fraction of the inorganic particles in the above range, the inorganic particles form a heat-resistant skeleton structure in the coating layer, effectively inhibit the thermal shrinkage of the coating layer, improve the safety performance of the battery, and at the same time reduce the risk of the inorganic particles falling off. Exemplarily, the mass fraction of the inorganic particles is 5%, 10%, 15%, 20%, 25%, 30%, or a value between any two of them.

[0207] In this application, the mass fraction of the inorganic particles can be tested by methods known in the art. The isolation film to be tested can be a prepared isolation film or an isolation film obtained by disassembling a battery. For example, the isolation film is obtained by disassembling the battery, the coating layer and the base film are peeled off, the coating layer is collected, and the mass m7 of the coating layer is weighed. The bonding particles or the bonding layer are dissolved with a suitable solvent, and then the inorganic particles are filtered out, and the mass m8 of the inorganic particles is weighed. The mass fraction of the inorganic particles is m7 / m8.

[0208] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the isolation film can be used to make an electrode assembly by a winding process or a stacking process.

[0209] In some embodiments, the battery cell can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and electrolyte.

[0210] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0211] The shape of the battery cell is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square battery cell 5 as an example.

[0212] In some embodiments, referring to Figure 2 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and the skilled person can select according to the specific actual needs.

[0213] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery module.

[0214] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other way. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0215] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0216] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person according to the application and capacity of the battery pack.

[0217] Figure 4 and Figure 5 is a battery pack 1 as an example. Referring to Figure 4 and Figure 5 , the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be provided on the lower box body 3 to form a closed space for receiving the battery module 4. The plurality of battery modules 4 can be arranged in the battery box in any way.

[0218] Electric device The application also provides a power utilization device, which comprises the secondary battery provided in the first aspect of the application. The secondary battery can comprise at least one of a battery cell, a battery module, or a battery pack. The secondary battery can be used as a power source of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can comprise a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0219] As the power utilization device, the battery cell, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0220] Figure 6 The power utilization device is taken as an example. The power utilization device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0221] The device taken as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as a power source.

[0222] Embodiment Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument used is not indicated by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0223] I. Preparation of the second graphite material and the second graphite material Preparation Example 1-1 Preparation of the first graphite material (material 1-1) Step 1: The oil-based calcined needle coke raw material is broken and shaped by using an air flow mill to obtain shaped material with Dv50 of 15 μm. Step 2: The above shaped material is granulated together by using granulation pitch (softening point of 125℃; coking value of 51%) as a granulating agent to obtain granulated material, wherein the mass ratio of the shaped material and the granulating agent is 88:7.

[0224] Step 3: The above granulated material is pre-carbonized at 1450℃ for 5.2h under a nitrogen atmosphere to obtain an intermediate.

[0225] Step 4: The above intermediate is subjected to graphitization at a high temperature of 3000°C, and the graphitized particles are screened and demagnetized to obtain the first graphite material.

[0226] Preparation Example 1-2 Preparation of the first graphite material (Material 1-2): The same method as in Preparation Example 1-1 is used to prepare Material 1-1, except that: Step 2: The above shaped material is granulated together with a granulating pitch (softening point: 118°C; coking value: 55%) as a granulating agent in a granulating kettle to obtain a granulated material, wherein the mass ratio of the shaped material and the granulating agent is 86:9.

[0227] Step 3: The above granulated material is subjected to pre-carbonization at 1650°C for 6 hours under a nitrogen atmosphere to obtain an intermediate.

[0228] Step 4: The above intermediate is subjected to graphitization at a high temperature of 3000°C, and the graphitized particles are screened and demagnetized to obtain the first graphite material.

[0229] Preparation Example 1-3 Preparation of the first graphite material (Material 1-3): The same method as in Preparation Example 1-1 is used to prepare Material 1-3, except that: Step 2: The above shaped material is granulated together with a granulating pitch (softening point: 136°C; coking value: 50%) as a granulating agent in a granulating kettle to obtain a granulated material, wherein the mass ratio of the shaped material and the granulating agent is 90:6.

[0230] Step 3: The above granulated material is subjected to pre-carbonization at 1350°C for 5 hours under a nitrogen atmosphere to obtain an intermediate.

[0231] Step 4: The above intermediate is subjected to graphitization at a high temperature of 3000°C, and the graphitized particles are screened and demagnetized, and a negative electrode coating layer is deposited on the surface of the first graphite material by a gas deposition method to obtain the first graphite material.

[0232] Preparation Example 2-1 Preparation of the second graphite material (Material 2-1): Step 1: An oil-based calcined needle coke raw material is broken and shaped by an air flow mill to obtain a shaped material; Step 2: The above shaped material is granulated together with a granulating pitch (softening point: 113°C; coking value: 66%) as a granulating agent in a granulating kettle to obtain a granulated material, wherein the mass ratio of the shaped material and the granulating agent is 90:6.

[0233] Step 3: The granulated material was pre-carbonized at 1480℃ for 4.7h under nitrogen atmosphere to obtain an intermediate (volume distribution particle size Dv50 of 16.3μm).

[0234] Step 4: The intermediate was graphitized at 3000℃, and the graphitized particles were screened and removed of magnetic particles to obtain a second graphite material.

[0235] Preparation Example 2-2 Preparation of the second graphite material (material 2-2): Material 2-2 was prepared by the same method as Preparation Example 2-1, except that the type of granulation pitch was adjusted. The parameters of the prepared material 2-2 are shown in Table 1-2.

[0236] Preparation Example 2-3 Preparation of the second graphite material (material 2-3): Material 2-3 was prepared by the same method as Preparation Example 2-1, except that the type of granulation pitch was adjusted. The parameters of the prepared material 2-3 are shown in Table 1-2.

[0237] II. Test of the second graphite material, the second graphite material (1) I D / I G test: The sample was tested by a Raman spectrometer.

[0238] The test conditions were as follows: excitation wavelength of 532nm, grating of 600 lines, objective lens of 50 times, integration time of 10s, cumulative number of 3 times, surface scanning, D peak and G peak intensity of 100 points were obtained, I D / I G of 100 points were calculated, 30 largest and smallest I D / I G were removed, and the average value of the remaining 40 points was the I D / I G of the material. The test instrument can be a Horiba LabRAM HR800 Raman spectrometer.

[0239] (2) Test of volume average particle size Dv50: According to GB / T 19077-2016, a laser particle size analyzer was used for determination. The test instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0240] (3) Test of BET specific surface area: According to GB / T 19587-2017, the nitrogen adsorption specific surface area analysis test method is used for testing, and the BET (Brunauer Emmett Teller) method is used for calculation. The test instrument can be a Tri-Star 3020 specific surface area and pore size analyzer of Micromeritics Company in the United States.

[0241] (4) Test of tap density: According to GB / T 5162-2006, a powder tap density tester is used for testing. The test instrument can use Dandong Bit BT-301, and the test parameters are as follows: vibration frequency 250±15 times / min, vibration amplitude 3±0.2 mm, vibration times 5000 times, and cylinder 25 mL.

[0242] (5) Test of thickness of negative electrode coating layer: The sample (material 1-3) is dispersed in ethanol and ultrasonically treated for 20 minutes, transferred to a micro-grid copper mesh for sample preparation, and the cross-sectional morphology of the coating layer is directly observed by high-resolution TEM, and the thickness is measured to be 33 nm.

[0243] Table 1-1

[0244] Table 1-2

[0245] III. Preparation of negative electrode slurry: Preparation Example 3-1 The first graphite material (see material 1-1 described in Table 1-1), the first binder (mass ratio of 2:1 of styrene-butadiene rubber and lithium polyacrylate), the first dispersant (lithium carboxymethyl cellulose), and the first conductive agent (mass ratio of 5:5 of carbon nanotube and conductive carbon black) are mixed in a mass ratio of 96.6:1.8:0.9:0.7 to prepare a first negative electrode slurry.

[0246] Preparation Example 3-2 The second graphite material (see material 2-1 described in Table 1-2), the second binder (mass ratio of 2:1.3 of styrene-butadiene rubber and lithium polyacrylate), the second dispersant (lithium carboxymethyl cellulose), and the second conductive agent (mass ratio of 5:5 of carbon nanotube and conductive carbon black) are mixed in a mass ratio of 97.8:1:0.7:0.5 to prepare a second negative electrode slurry.

[0247] Preparation Example 3-3 The negative active material (material 1-1 and material 2-1 with a mass ratio of 5:5), the second binder (butadiene-styrene rubber and lithium polyacrylate with a mass ratio of 2:1), the second dispersing agent (lithium carboxymethyl cellulose), and the second conductive agent (carbon nanotubes and conductive carbon black with a mass ratio of 5:5) were mixed in a mass ratio of 96.9:1.8:0.8:0.5 to prepare a third negative electrode slurry.

[0248] Example 1 Preparation of the secondary battery: 1. Preparation of the positive electrode sheet: The positive active material (the first positive active material, lithium iron phosphate), conductive carbon black, polyvinylidene fluoride (PVDF), and the positive electrode dispersing agent (polyethylene glycol octylphenyl ether) were mixed in a mass ratio of 97.6:0.1:1.8:0.5, and then a solvent N-methyl pyrrolidone was added to obtain a positive electrode slurry. The positive electrode slurry was coated on both surfaces of the positive electrode current collector aluminum foil, and then dried and cold-pressed to obtain the positive electrode sheet.

[0249] 2. Preparation of the negative electrode sheet: The first negative electrode slurry and the second negative electrode slurry were simultaneously extruded by a double-cavity coating device, wherein the mass ratio of the first negative electrode slurry and the second negative electrode slurry was 5:5, and then dried and cold-pressed to obtain the negative electrode sheet. The second negative electrode slurry was coated on the negative electrode current collector (copper foil) to form a second film layer, and the first negative electrode slurry was coated on the side of the second negative electrode slurry away from the negative electrode current collector to form a first film layer. Then, the negative electrode sheet was obtained after drying, cold-pressing, and slitting.

[0250] 3. Preparation of the electrolyte: The mixture of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) was mixed in a volume ratio of 3:7 to form an organic solvent, a film-forming agent (barium sulfate with a mass ratio of 2.5%) was added, and LiPF6 was dissolved in the above organic solution to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0251] 4. Isolation film: A polyethylene film with a thickness of 5 μm was used, and a coating layer was coated on both sides of the base film. The coating layer included heat-resistant particles, and the heat-resistant particles included boehmite particles (inorganic particles) and a bonding layer arranged on the surface of the boehmite particles.

[0252] 5. Preparation of the secondary battery: The above positive electrode sheet, isolation film, and negative electrode sheet were stacked in order, with the isolation film between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then the electrode assembly was formed by bending and winding. The electrode assembly was placed in an outer package, dried, and then the above prepared electrolyte was injected. After vacuum packaging, standing, formation, shaping, and other processes, the secondary battery was obtained.

[0253] V. Test of morphology of negative electrode sheet A cross-section of the negative electrode sheet was cut using an argon ion cross-section polisher (for example, an IB-09010 CP argon ion cross-section polisher from JEOL Ltd., Japan), and a SEM photograph of the cross-section of the negative electrode sheet was captured by a scanning electron microscope (HR-TEM Talos F200) as shown in FIG. 2. Figure 7 As can be seen from FIG. 2, the negative electrode sheet comprises a negative current collector, a second film layer disposed on the surface of the negative current collector, and a first film layer disposed on the surface of the second film layer. Figure 7

[0254] VI. Test of performance of secondary battery 1. Test of fast charging performance At 25°C, the secondary battery was charged at a constant current of 0.33C to a charge cut-off voltage of 3.65V, and then charged at a constant voltage until the current was 0.05C. After standing for 5 min, the secondary battery was discharged at a constant current of 0.33C to a discharge cut-off voltage of 2.5V, and the actual capacity was recorded as C0.

[0255] Then the secondary battery was charged at a constant current of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2C0, 2.3C0, 2.5C0, and 3.0C0, respectively, to a charge cut-off voltage of 3.65V or a negative electrode cut-off potential of 0mV (whichever is reached first), and after each charging was completed, the secondary battery was discharged at a constant current of 1C0 to a discharge cut-off voltage of 2.5V. The negative electrode potential corresponding to 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC (State of Charge) at different charging rates was recorded.

[0256] The charging rate-negative electrode potential curve at different SOC states was plotted, and the charging rate corresponding to a negative electrode potential of 0V at different SOC states was obtained by linear fitting. This charging rate is the charging window at the SOC state, and is denoted as C 10%SOC , C 20%SOC , C 30%SOC , C 40%SOC , C 50%SOC , C 60%SOC , C 70%SOC , and C 80%SOC , respectively.

[0257] According to the following formula:

[0258] The charging time T (on the premise that the secondary battery does not deposit lithium) from 10% SOC to 80% SOC of the secondary battery was calculated to be min. The test results are recorded in Table 2. ​

[0259] 2. Test of service life: (1) Test of cycle life: Stand for 5 min; Charge at a constant current of 0.33 C to a charge cut-off voltage of 3.65 V, and then charge at a constant voltage of 3.65 V to a current of 0.05 C; Stand for 5 min; Discharge at a constant current of 1 C to a discharge cut-off voltage of 2.0 V, and record the discharge capacity D1 of the first cycle; Cycle the above steps n times, and record the discharge capacity Dn of the nth cycle; Dn = D1 * 70%, and N is the cycle number. The test results are recorded in Table 2.

[0260] (2) Test of storage life: Stand for 5 min; Charge at a constant current of 0.33 C to 3.65 V, and then charge at a constant voltage of 3.65 V to a current of 0.05 C, and record the discharge capacity of the battery as C0.

[0261] Place the fully charged battery in a 60°C oven for 30 days (720 h), and take out the battery; Place the battery in a 25°C environment and discharge at 0.33 C, and record the discharge capacity as C1. Capacity retention rate = (C1 / C0) * 100%, recorded as "storage 720 h capacity retention rate". The test results are recorded in Table 2.

[0262] Comparative Example 1 The secondary battery of Comparative Example 1 was prepared by the same method as Example 1, except that: In the preparation process of the negative electrode sheet, the first negative electrode slurry was coated on both sides of the negative electrode current collector to form a first film layer, and the second negative electrode slurry was coated on the side of the first negative electrode slurry away from the negative electrode current collector to form a second film layer. Then, drying, cold pressing, and slitting were performed to obtain the negative electrode sheet.

[0263] Comparative Example 2 The secondary battery of Comparative Example 2 was prepared by the same method as Example 1, except that: In the preparation process of the negative electrode sheet, the third negative electrode slurry was coated on both sides of the negative electrode current collector, and then drying, cold pressing, and slitting were performed to obtain the negative electrode sheet. The coating weight of the third negative electrode slurry was 130 mg / 1540.25 mm 2 .

[0264] Comparative Example 3 The secondary battery of Comparative Example 3 was prepared by the same method as Example 1, except that: In the preparation process of the negative electrode sheet, a first negative electrode slurry is coated on both sides of the negative electrode current collector, followed by drying, cold pressing, and slitting to obtain the negative electrode sheet. The coating weight of the first negative electrode slurry is 130 mg / 1540.25 mm. 2 .

[0265] Comparative Example 4 Comparative Example 4 and Example 1 were prepared using the same method for secondary batteries, the difference being: In the preparation of the negative electrode sheet, a second negative electrode slurry is coated on both sides of the negative electrode current collector, followed by drying, cold pressing, and slitting to obtain the negative electrode sheet. The coating weight of the second negative electrode slurry is 130 mg / 1540.25 mm. 2 .

[0266] Comparative Example 5 Comparative Example 5 and Example 1 were prepared using the same method for secondary batteries, the difference being: Material 1-1 in the first negative electrode active slurry was replaced with material 1-2. The performance of the secondary batteries prepared in Comparative Examples 1 to 5 was tested in the same manner as in Example 1, and the test results are recorded in Table 2.

[0267] Table 2

[0268] The data in Table 2 shows that, compared to Comparative Examples 1 to 5, the negative electrode film layer in the secondary battery prepared in Example 1 includes a first film layer and a second film layer disposed between the first film layer and the negative electrode current collector. The first film layer includes a first negative electrode active material (I... D / I G =0.51), the second film layer includes the second negative electrode active material, and the secondary battery prepared in Example 1 takes into account both fast charging performance and service life.

[0269] Example 2 Example 2 uses the same method as Example 1 to prepare a secondary battery, the difference being that the second negative electrode slurry is replaced with a third negative electrode slurry during the preparation of the negative electrode sheet.

[0270] Testing of negative electrode morphology A cross-section of the second film layer in the negative electrode sheet prepared in Example 2 was captured using an argon ion cross-section polisher (e.g., the JEOL IB-09010 CP type argon ion cross-section polisher). A SEM image of the cross-section of the second film layer was then acquired using a scanning electron microscope (HR-TEM Talos F200). Figure 8 As shown, from Figure 8 As can be seen, the second film layer consists of large and small particles. The large particles are the second graphite material, and the small particles are the first graphite material.

[0271] Examples 3-6 Examples 3-6 were prepared in the same way as Example 2, except that: In the preparation of the negative electrode sheet, the mass ratio of the first graphite material to the second graphite material in the third negative electrode slurry and / or the mass ratio of the first negative electrode slurry to the second negative electrode slurry (corresponding to the thickness ratio of the first film layer to the second film layer) was adjusted according to Table 3.

[0272] Examples 7 and 8 Examples 7 and 8 were prepared in the same way as Example 2, except that, in the preparation of the negative electrode sheet, the mass ratio of the first graphite material to the second graphite material in the third negative electrode slurry and / or the mass ratio of the first negative electrode slurry to the second negative electrode slurry (corresponding to the thickness ratio of the first film layer to the second film layer) was adjusted according to Table 3. The performance of the secondary batteries prepared in Examples 2-8 was tested in the same way as Example 1, and the test results are recorded in Table 3.

[0273] Table 3

[0274] The "mass ratio" in Table 3 is the mass ratio of the second graphite material to the first graphite material.

[0275] As can be seen from the data in Table 3, when the second film layer comprises the first graphite material and the second graphite material, the fast-charging performance of the prepared secondary battery is further improved.

[0276] Example 9 Example 9 was prepared in the same way as Example 2, except that: In the first negative electrode slurry, the mass ratio of the first graphite material, the first binder, the first dispersant (lithium carboxymethyl cellulose), and the first conductive agent was 97.6:2:0.3:0.1. In the preparation of the third negative electrode slurry, the mass ratio of the negative electrode active material, the second binder, the second dispersant, and the second conductive agent was 97.6:2:0.3:0.1.

[0277] The thickness of the negative current collector was 4 μm.

[0278] The coating weight of the first negative electrode slurry was 32 mg / 1540.25 mm 2 . The coating weight of the third negative electrode slurry was 78 mg / 1540.25 mm 2 .

[0279] Example 10 Example 10 was prepared in the same way as Example 2, except that: The mass ratio of the first graphite material, the first binder, the first dispersant (lithium carboxymethyl cellulose), and the first conductive agent in the first negative electrode slurry is 96.4:0.1:1.5:2. In the configuration process of the third negative electrode slurry, the mass ratio of the negative electrode active material, the second binder, the second dispersant, and the second conductive agent is 96.4:0.1:1.5:2.

[0280] The thickness of the negative electrode current collector is 8 μm.

[0281] The coating weight of the first negative electrode slurry is 65 mg / 1540.25 mm 2 The coating weight of the third negative electrode slurry is 75 mg / 1540.25 mm 2 .

[0282] Test of the compaction density of the negative electrode sheet: The negative electrode sheet can be wiped off the negative electrode film layer on one side, cut into a small disc with an area of S11, weighed, and recorded as M11. Then the negative electrode film layer of the above weighed negative electrode sheet is wiped off, the weight of the negative electrode current collector is weighed and recorded as M10, and the thickness H10 is measured. The single-side coating weight of the negative electrode sheet = (M11-M10) / S11, the thickness of the negative electrode film layer = H11-H10, and the compaction density of the negative electrode sheet = the single-side coating weight of the negative electrode film layer / the thickness of the negative electrode film layer. The test results are recorded in Table 4-2.

[0283] In the same way as in Example 1, the performance of the secondary batteries prepared in Examples 9 and 10 is tested, and the test results are recorded in Table 4-3.

[0284] Table 4-1

[0285] Table 4-2

[0286] Table 4-3

[0287] From the data in Tables 4-1 to 4-3, it can be seen that when the positive electrode sheet meets the above conditions, the obtained secondary battery can balance the fast charging performance and the service life.

[0288] Examples 11 to 15 Examples 11 to 15 and Example 2 use the same method to prepare secondary batteries, the difference is that: The batteries are prepared using the first positive electrode active material recorded in Table 5-1. The parameters of each first positive electrode active material are recorded in Table 5-2.

[0289] The performance of the secondary batteries prepared in Examples 11 to 15 was tested in the same manner as in Example 1, and the test results are recorded in Table 5-3.

[0290] Table 5-1

[0291] Table 5-2

[0292] Table 5-3

[0293] As can be seen from the data in Tables 5-1 to 5-3, when the positive active material comprises a lithium-containing phosphate, the resulting secondary battery can have both fast-charging performance and service life, and when the positive electrode coating layer comprises a fast-ion conductor material and / or a carbon material, the fast-charging performance of the prepared secondary battery is further improved.

[0294] Examples 16 to 18 Examples 16 to 18 were prepared in the same manner as in Example 2, except that at least one of the ratio of the components in the positive active material, the coating weight of the positive electrode slurry, and the thickness of the positive electrode current collector was adjusted according to Table 6-1.

[0295] Test of the compaction density of the positive electrode tab: The positive electrode tab was first wiped to remove the positive electrode film layer on one side, cut into a small disc with an area of S21, weighed, and recorded as M21, and its thickness H21 was measured. Then the positive electrode film layer of the above weighed positive electrode tab was wiped off, the weight of the positive electrode current collector was weighed and recorded as M20, and its thickness H20 was measured. The single-side coating weight of the positive electrode tab = (M21-M20) / S21, the thickness of the positive electrode film layer = H21-H20, and the compaction density of the positive electrode tab = the single-side coating weight of the positive electrode film layer / the thickness of the positive electrode film layer. The test results are recorded in Table 6-1. The performance of the secondary batteries prepared in Examples 16 to 18 was tested in the same manner as in Example 1, and the test results are recorded in Table 6-2.

[0296] Table 6-1

[0297] The "mass ratio" in Table 6-1 is the mass ratio of the first positive active material and the second positive active material.

[0298] Table 6-2

[0299] As can be seen from the data in Tables 6-1 to 6-2, when the positive electrode sheet satisfies the above conditions, the obtained secondary battery can have both fast charging performance and service life.

[0300] Examples 19 and 20 Examples 19 and 20 and Example 2 were used to prepare secondary batteries in the same manner, except that the type or amount (mass ratio in the positive electrode film layer) of the positive electrode dispersant and the type or amount (mass ratio in the electrolyte) of the additive were adjusted as described in Table 7-1.

[0301] The performance of the secondary batteries prepared in Examples 19 and 20 was tested in the same manner as in Example 1, and the test results are shown in Table 7-2.

[0302] Table 7-1

[0303] Table 7-2

[0304] As can be seen from the data in Tables 7-1 and 7-2, when the mass ratio of the positive electrode dispersant in the positive electrode sheet is 0.3% to 5% and the mass ratio of the additive in the electrolyte is 1% to 2.3%, the obtained secondary battery can have both fast charging performance and service life.

[0305] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration and exerting the same effects as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes obtained by applying various modifications to the embodiments or by combining some of the constituent elements of the embodiments within the scope of the gist of the present application are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: The electrode assembly includes a negative electrode and a positive electrode. The positive electrode sheet includes a positive current collector and a positive electrode film layer disposed on at least one side surface of the positive current collector. The positive electrode film layer includes a positive electrode active material. The positive electrode active material includes a first positive electrode active material, which includes a lithium phosphate with an olivine structure. The compacted density of the negative electrode tab is 1.3 g / cm 3 to 1.65 g / cm 3 The negative electrode tab includes a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a first film layer and a second film layer disposed between the first film layer and the negative electrode current collector. The first film layer includes a first negative active material including a first graphite material having an I D / I G of 0.5 to 0.

9. The second film layer includes a second negative active material including a second graphite material having I D / I G of 0.05 to 0.2; wherein I D represents a D peak intensity of a Raman spectrum at 1350±50 cm -1 -1; and I G represents a G peak intensity of a Raman spectrum at 1580±50 cm -1 -1.

2. The secondary battery according to claim 1, characterized by The ratio of the average thickness of the first film layer to the average thickness of the second film layer is (3-5):(5-7).

3. The secondary battery according to claim 1, characterized in that, The volume average particle size Dv50 of the first graphite material is 9.2 μm to 15.5 μm, and / or, The volume average particle size Dv50 of the second graphite material is 16.3 μm to 25.5 μm.

4. The secondary battery according to claim 1, characterized in that, The BET specific surface area of the first graphite material is 0.3 m 2 / g to 3 m 2 / g, and / or, The BET specific surface area of the second graphite material is 0.5 m 2 / g to 5 m 2 / g.

5. The secondary battery according to claim 1, characterized in that, The tap density of the first graphite material is 0.7 g / cm 3 up to 1.6 g / cm 3 and / or, The tap density of the second graphite material is 0.8 g / cm 3 up to 1.5 g / cm 3 .

6. The secondary battery according to claim 1, characterized by The first negative electrode active material further includes a negative electrode coating layer distributed on the surface of the first graphite material, the negative electrode coating layer comprising amorphous carbon.

7. The secondary battery according to claim 6, characterized by The thickness of the negative electrode coating layer is 10 nm to 100 nm.

8. The secondary battery according to claim 1, characterized by The second negative electrode active material also includes the first graphite material, and the mass ratio of the second graphite material to the first graphite material in the second negative electrode active material is (3-5):(5-7).

9. The secondary battery according to claim 1, characterized by The first membrane layer further includes a first adhesive, which comprises at least one of styrene-butadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, or carboxymethyl chitosan, and / or, The second membrane layer further includes a second adhesive, which includes at least one of styrene-butadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, or carboxymethyl chitosan.

10. The secondary battery according to claim 9, characterized by The first adhesive comprises at least one of styrene-butadiene rubber, lithium polyacrylate, and polyacrylate, and / or, The second adhesive includes at least one of styrene-butadiene rubber, lithium polyacrylate, and polyacrylate.

11. The secondary battery according to claim 9, characterized by The first adhesive in the first film layer accounts for 0.1% to 2% of the total mass, and / or, The second adhesive in the second film layer accounts for 0.1% to 2% of the total mass.

12. The secondary battery according to claim 1, characterized by The first film layer further includes a first dispersant, which includes at least one of lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, and / or... The second film layer further includes a second dispersant, which includes at least one of lithium carboxymethyl cellulose and sodium carboxymethyl cellulose.

13. The secondary battery according to claim 12, characterized by The first dispersant comprises lithium carboxymethyl cellulose, and / or, The second dispersant includes lithium carboxymethyl cellulose.

14. The secondary battery according to claim 12, characterized by The mass percentage of the first dispersant in the first film layer is 0.3% to 1.5%, and / or, The mass percentage of the second dispersant in the second film layer is 0.3% to 1.5%.

15. The secondary battery according to claim 1, characterized by The first film layer further includes a first conductive agent, which includes at least one of carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black, and / or... The second film layer further comprises a second conductive agent, and the second conductive agent comprises at least one of carbon dots, graphene, carbon nanofibers, carbon nanotubes and conductive carbon black.

16. The secondary battery according to claim 15, characterized by The first conductive agent comprises carbon nanotubes and conductive carbon black, and / or, The second conductive agent comprises carbon nanotubes and conductive carbon black.

17. The secondary battery according to claim 15, characterized by The mass percentage of the first conductive agent in the first film layer is 0.1% to 2%, and / or, The mass percentage of the second conductive agent in the second film layer is 0.1% to 2%.

18. The secondary battery according to claim 1, characterized by The negative electrode film layer satisfies at least one of the following conditions: (1) The coating weight of the negative electrode film layer provided on one side of the negative electrode current collector is 80 mg / 1540.25 mm 2 to 130 mg / 1540.25 mm 2 ; (2) The thickness of the negative electrode film layer arranged on one side of the negative electrode current collector is 40 μm to 75 μm.

19. The secondary battery according to claim 1, characterized by The thickness of the negative electrode current collector is 4 μm to 8 μm.

20. The secondary battery according to claim 1, characterized by The lithium-containing olivine structure phosphate comprises a compound as shown in formula (I): , formula (I); In the formula (I), M 1 at least one selected from V, Nb, Ti, Co, Ni, Sc, Ge, Mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, Ag, Sn, and Pb, 0≤x≤1, 0≤y<1.

21. The secondary battery according to claim 1, characterized by The first positive electrode active material further comprises a positive electrode coating layer, the positive electrode coating layer is arranged on at least part of the surface of the lithium-containing phosphate, and the positive electrode coating layer comprises at least one of a fast ion conductor material and a carbon material.

22. The secondary battery according to claim 21, characterized by In the positive electrode coating layer, the mass ratio of the fast ion conductor material to the carbon material is (0-100):(100-0).

23. The secondary battery according to claim 21, characterized by The positive electrode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a fast ion conductor material, and the second coating layer comprises a carbon material; The first coating layer is arranged between the lithium-containing phosphate and the second coating layer; Or, the second coating layer is arranged between the lithium-containing phosphate and the first coating layer.

24. The secondary battery according to claim 21, characterized by The fast ion conductor material comprises a compound as shown in formula (II): Formula (II); In the formula (II), M 2 is at least one selected from the group consisting of Ti, Zr, Hf, Ge and Sn, 0 ≤ b ≤ 1.

25. The secondary battery according to claim 21, characterized by The mass percentage of carbon elements in the first positive electrode active material is 1% to 1.5%.

26. The secondary battery according to claim 1, characterized by The first positive electrode active material satisfies at least one of the following conditions: (1) the first positive electrode active material has a BET specific surface area of 12 m 2 / g to 16 m 2 / g; (2) the tap density of the first positive electrode active material is 0.8 g / cm 3 to 1.3 g / cm 3 ; (3) The volume average particle size Dv50 of the first positive electrode active material is 1 μm to 3 μm; (4) the first positive electrode active material has a compaction density of 2.4 g / cm3 to 2.6 g / cm3 under 50,000 N 3 . 3 .

27. The secondary battery according to claim 1, characterized by The positive electrode active material further comprises a second positive electrode active material, and the second positive electrode active material comprises a lithium transition metal oxide.

28. The secondary battery according to claim 27, characterized by The mass ratio of the first positive electrode active material to the second positive electrode active material is (99-90):(1-10).

29. The secondary battery according to claim 1, characterized by The positive electrode film layer satisfies at least one of the following conditions: (1) The thickness of the positive electrode film layer arranged on one side of the positive electrode current collector is 60 μm to 130 μm; (2) The coating weight of the positive electrode film layer provided on one side of the positive electrode current collector is 200 mg / 1540.25 mm 2 to 300 mg / 1540.25 mm 2 ; (3) the compaction density of the positive electrode plate is 2 g / cm 3 to 3 g / cm 3 .

30. The secondary battery according to claim 1, characterized by The thickness of the positive electrode current collector is 10 μm to 18 μm.

31. The secondary battery according to claim 1, characterized by The positive electrode film layer further comprises a positive electrode dispersant, and the positive electrode dispersant comprises at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone and sodium carboxymethyl cellulose.

32. The secondary battery according to claim 31, characterized by The mass percentage of the positive electrode dispersant relative to the positive electrode film layer is 0.3% to 5%.

33. The secondary battery according to claim 1, characterized by The secondary battery further comprises an electrolyte, and the electrolyte comprises an electrolyte salt and a solvent; The solvent comprises at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone. The electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorobisoxalate borate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

34. The secondary battery of claim 33, wherein The electrolyte further includes an additive, the additive including at least one of barium sulfate, polytrifluoroethyl methyl acrylate, bicyclic sulfate, tricyclic sulfate, tris(trimethylsilyl)phosphate, and vinylene carbonate.

35. The secondary battery of claim 34, wherein In the electrolyte, the additive has a mass ratio of 1% to 5%.

36. The secondary battery of claim 33, wherein The electrolyte has an electrical conductivity of 10 mS / cm to 18.5 mS / cm.

37. The secondary battery according to claim 1, characterized by The secondary battery further includes a separator, the separator including a base film having a thickness of 3 μm to 18 μm.

38. The secondary battery of claim 37, wherein, The separator further includes a coating layer disposed on at least one side of the base film, the coating layer including heat-resistant particles interwoven to form a pore structure.

39. The secondary battery according to claim 1, characterized by The electrode assembly is a jelly-roll electrode assembly.

40. An electrical device, comprising: A secondary battery including any one of claims 1 to 39.

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