Secondary batteries and electric devices

Abstract

The present application provides a secondary battery and an electric device and relates to the field of batteries. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive current collector and a positive film layer provided on at least one surface of the positive current collector, and the compaction density of the positive film layer is 2.0 g / cm³ to 3.0 g / cm³; the negative electrode sheet comprises a negative current collector and a negative film layer located on at least one surface of the negative current collector, and the compaction density of the negative film layer is 1.4 g / cm³ to 1.85 g / cm³; the separator comprises a base film, the thickness of the base film is 4 μm to 12 μm, the base film has nanopores, and the average pore size of the nanopores is 10 nm to 300 nm.

Description

Technology Field

[0001] The present application is filed based on a Chinese patent application with application number 202510932503.0, filing date July 7, 2025, and title of invention "secondary battery and electric device", and claims priority of said Chinese patent application, said Chinese patent application is incorporated by reference into the present application.

[0002] This application relates to the field of battery technology, and in particular to secondary batteries and electric devices. Background Technology

[0003] Recently, as the scope of applications for secondary batteries gradually expands, they are being widely applied in various fields, including energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0004] As secondary batteries have made rapid progress, demands regarding aspects such as energy density and safety performance of secondary batteries have increased in actual applications.

[0005] In related technologies, the energy density of a battery is generally improved by increasing the compaction density of the film layer. However, this method has a significant disadvantage in that increasing the compaction density simultaneously increases the amount of heat released from within the battery, which further leads to a decrease in the battery's safety performance.

[0006] Therefore, considering the energy density and safety performance of batteries is becoming an urgent technical challenge that needs to be addressed.

[0007] This application has been made in consideration of the aforementioned problem and aims to provide a secondary battery and an electric device. The secondary battery is designed to combine high energy density and enhanced safety performance.

[0008] To achieve the above-mentioned objective, the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator in a first aspect thereof, wherein the positive electrode sheet comprises a positive current collector and a positive film layer provided on at least one surface of the positive current collector, and the compaction density of the positive film layer is 2.0 g / cm³ 3 Up to 3.0 g / cm² 3 The cathode sheet comprises a cathode current collector and a cathode film layer located on at least one surface of the cathode current collector, and the compaction density of the cathode film layer is 1.4 g / cm³ 3 Up to 1.85 g / cm² 3 The separator includes a base film, the thickness of the base film is 4 μm to 12 μm, the base film has nanopores, and the average pore size of the nanopores is 10 nm to 300 nm.

[0009] In this application, the compaction density of the anode film layer is 2.0 g / cm² 3 Up to 3.0 g / cm² 3 Controlled by, and the compaction density of the cathode film layer is 1.4 g / cm³ 3 Up to 1.85 g / cm² 3 By controlling it, it is advantageous for the battery to achieve high energy density. The present application uses a base film with a thickness of 4 μm to 12 μm, which reduces the impact on battery safety performance caused by the base film thickness being excessively thin (less than 4 μm), while simultaneously reducing the adverse impact on battery energy density caused by the base film thickness being excessively thick (more than 12 μm). Thus, the battery can have improved battery safety performance and simultaneously secure high energy density. In addition, the base film is provided with nanopores, and the average pore size of the nanopores is 10 nm to 300 nm. This helps to improve the mobility of lithium ions and is also advantageous for simultaneously considering the suppression of lithium dendrite growth, thereby further improving the safety performance of the battery.

[0010] Specifically, a base film with a thickness within the aforementioned range can maintain structural stability at high temperatures and effectively reduce the risk of short circuits between the anode and cathode. In particular, during battery thermal runaway, a base film with a stable structure can suppress the occurrence of adverse reactions through physical isolation; this lowers the maximum temperature during thermal runaway, reduces the risk of thermal diffusion, and improves the safety performance of the battery. Furthermore, since the base film thickness is within the aforementioned range, it is advantageous to minimize the adverse effects of the base film on battery energy density, thereby enabling the battery to maintain high energy density.

[0011] In some embodiments, the thickness of the base film is 5 μm to 9 μm. Since the thickness of the base film is within the above-described range, it is advantageous to consider both the energy density and safety performance of the battery.

[0012] In some embodiments, the porosity of the base film is 20% to 70%. This helps to improve the mobility of lithium ions while also being advantageous for considering the growth of lithium dendrites, thereby further improving the safety performance of the battery.

[0013] In some embodiments, the separator further comprises a coating layer provided on at least one side of a base film, wherein the coating layer contains heat-resistant particles, and the heat-resistant particles are interwoven to form a porous structure. Compared to a coating layer without a porous structure, in the above embodiment, the heat-resistant particles are interwoven to form a porous structure, which is advantageous for reducing the inhibition of ion transport by the coating layer, thereby improving ion transport efficiency. Additionally, the coating layer contains heat-resistant particles, and the volume of the heat-resistant particles changes little with temperature. By providing a coating layer containing heat-resistant particles on the surface of the base film, it is advantageous for suppressing the thermal shrinkage rate of the base film, thereby further reducing the risk of anode and cathode short circuits and improving the safety performance of the battery.

[0014] In some embodiments, the thickness of the coating layer provided on one side of the base film is 0.011 μm to 3 μm. This is advantageous for the battery to achieve high energy density on one hand, and on the other hand, for the coating layer to better suppress the thermal shrinkage rate of the base film, thereby further improving the safety performance of the battery.

[0015] In some embodiments, the average particle size of the heat-resistant particles is 5 nm to 185 nm. The heat-resistant particles having an average particle size of 5 nm to 185 nm can form a coating layer with a stable support network structure, support the base film, and simultaneously suppress thermal shrinkage of the base film, thereby improving the safety performance of the battery.

[0016] In some embodiments, the particle areal density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 Up to 2.5 mg / 1540.25 cm 2 This makes it advantageous for the battery to achieve high energy density, while also making it advantageous for the heat-resistant particles to suppress thermal shrinkage of the base film, thereby improving the safety performance of the battery.

[0017] In some embodiments, along the thickness direction of the base film, the heat-resistant particles include a first heat-resistant particle. The first heat-resistant particle is distributed on the surface of the base film, and the first heat-resistant particle can directly suppress the thermal shrinkage of the base film, which is advantageous for further improving the safety performance of the battery and can also be taken into account for the energy density of the battery.

[0018] In some embodiments, along the thickness direction of the base film, the heat-resistant particles comprise a first heat-resistant particle and a second heat-resistant particle; wherein the first heat-resistant particle is distributed on the surface of the base film, and the second heat-resistant particle is laminated on one side away from the base film where the first heat-resistant particle is located. In the above embodiment, the first heat-resistant particle and the second heat-resistant particle are laminated in the thickness direction of the base film, which is advantageous for forming a thicker coating layer, and the thicker coating layer acts as a more effective physical barrier, which can reduce chemical erosion of the electrolyte against the base film and simultaneously buffer friction of the sheets (anode sheet, cathode sheet) against the base film, thereby further improving the safety performance of the battery.

[0019] In some embodiments, the heat-resistant particles comprise inorganic particles and adhesive particles. In the above embodiment, the adhesive particles act as a mediator to tightly bind the inorganic particles. This allows the inorganic particles to form a single stable overall structure, thereby improving the mechanical strength and stability of the coating layer and better suppressing thermal shrinkage of the base film.

[0020] In some embodiments, the heat-resistant particles comprise inorganic particles and an adhesive layer provided on at least a portion of the surface of the inorganic particles. In the above embodiment, the adhesive layer is provided on the surface of the inorganic particles, which is advantageous for improving the bonding strength between the inorganic particles and the base film, reducing the risk of the inorganic particles peeling off, and improving the safety performance and service life of the battery.

[0021] In some embodiments, the inorganic particles comprise 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-described material changes little with temperature and is advantageous for use as inorganic particles to further suppress thermal shrinkage of the base film, thereby further improving the safety performance of the battery.

[0022] In some embodiments, the mass ratio of inorganic particles in the coating layer is 5% to 30%. This makes it advantageous for the inorganic particles to form a heat-resistant framework structure in the coating layer, effectively suppresses thermal shrinkage of the coating layer, and improves the safety performance of the battery while reducing the risk of the inorganic particles peeling off.

[0023] In some embodiments, the cathode film layer comprises a first film layer and a second film layer disposed between the first film layer and a cathode current collector, the first film layer comprises a first cathode active material, the first cathode active material comprises a first graphite material, and I of the first graphite material D / I G is 0.4 to 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 I of the second graphite material D / I G is 0.05 to 0.2; where I D 1350±50cm in the Raman spectrum -1 Indicates the D peak intensity at the position, and I G 1580±50cm in the Raman spectrum -1 It indicates the G peak intensity of the location.

[0024] I of the first graphite material used in this application D / I Gis 0.4 to 0.9, indicating that a large number of defects exist on the surface of the first graphite material, and these defects can serve as additional active sites for lithium ion insertion. Providing this first graphite material with many surface defects on the outer layer (first film layer) of the cathode sheet is advantageous for increasing the possibility of contact between the additional active sites and the electrolyte, thereby improving the high-speed charging performance of the battery. Based thereon, as the inner layer (second film layer) of the cathode sheet, I D / I G A second graphite material having a value of 0.05 to 0.2 is used, and the second graphite material has few surface defects and a relatively complete structure, which is advantageous for reducing irreversible loss of lithium ions and thereby extending the service life of the battery.

[0025] 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 amorphous carbon has a relatively loose structure and has a rich pore structure. These pores can provide more diffusion pathways for lithium ions and shorten the diffusion path of lithium ions in the electrode material. By providing amorphous carbon on the surface of the first graphite material, lithium ions can pass through the negative electrode coating layer more quickly and reach the interior of the first graphite material, thereby improving the high-speed charging performance of the battery.

[0026] In some embodiments, the thickness of the negative electrode coating layer is 10 nm to 100 nm. Since the thickness of the negative electrode coating layer is within the above-described range, it is advantageous for the secondary battery to consider both fast charging performance and energy density.

[0027] In some embodiments, the second film layer further comprises a first graphite material. The first graphite material can improve the fast charging performance of the battery. In the above embodiments, by arranging the second graphite material and the first graphite material in the second film layer, it is advantageous to consider the improvement of the fast charging performance of the battery.

[0028] In some embodiments, the mass ratio of the second graphite material to the first graphite material in the second film layer is (3 to 5):(5 to 7). By controlling the mass ratio of the second graphite material to the first graphite material in the second film layer to within the range described above, it is advantageous to further consider the improvement of the battery's fast charging performance and service life.

[0029] In some embodiments, the coating weight of the cathode film layer is 80 mg / 1540.25 mm 2 Up to 170 mg / 1540.25 mm 2 This is advantageous for improving the quantity of lithium ions emitted by the negative electrode film layer per unit area, and further improves the energy density of the battery.

[0030] In some embodiments, the thickness of the cathode film layer provided on a single side of the cathode current collector is 40 μm to 75 μm. This makes it advantageous for the cathode film layer to have high capacity and high lithium-ion and electron transport performance, and furthermore, makes it advantageous for the secondary battery to have high energy density and fast charging performance.

[0031] In some embodiments, the thickness of the negative current collector is 4 μm to 8 μm. When the thickness of the negative current collector is within the above-described range, on the one hand, it is advantageous for the battery to achieve high energy density, on the other hand, it is advantageous for reducing the risk of cracking of the negative current collector, and furthermore, extends the service life of the battery.

[0032] In some embodiments, the positive film layer comprises a positive active material, the positive active material comprises a first positive active material, and the first positive active material comprises a lithium-containing phosphate having an olivine structure. The lithium-containing phosphate having an olivine structure has a stable three-dimensional crystal lattice structure, and during the insertion and extraction of lithium ions, the structure can maintain relative stability, so structural collapse and deformation do not easily occur, and as a result, the lithium-containing phosphate having an olivine structure is not damaged through multiple charge-discharge cycles, thereby extending the service life of the battery.

[0033] In some embodiments, the lithium-containing phosphate of the olivine structure comprises a compound represented by formula (I):

[0034] LiFe 1-x-y Mn x M 1 y PO4, formula (I);

[0035] In Equation (I), M 1 The element is selected from at least one of V, Nb, Ti, Co, Ni, Sc, Ge, mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, A g, Sn, and Pb, where 0≤x≤1 and 0≤y<1. The crystal lattice structure of the above-described lithium-containing phosphate is stable, and phase changes do not occur easily, thereby further improving the safety performance of the secondary battery.

[0036] In some embodiments, the first positive active material further comprises a positive coating layer, the positive coating layer is provided on at least a portion of the surface of the lithium-containing phosphate, and the positive coating layer comprises at least one of a high-speed ion conductor material and a carbon material.

[0037] The carbon material has a loose porous shape, allowing the electrolyte and the lithium iron phosphate substrate to contact each other sufficiently effectively, thereby improving the infiltration performance of the electrolyte into the anode film layer and further enhancing the high-speed charging performance of the secondary battery.

[0038] High-speed ion conductor materials have high ion conductivity, and selecting and using an anode coating layer containing high-speed ion conductor materials is advantageous for improving the high-speed charging performance of the battery.

[0039] In some embodiments, the mass ratio of the high-speed ion conductor material and the carbon material in the anode coating layer is (0 to 100):(100 to 0). Controlling the mass ratio of the high-speed ion conductor material and the carbon material within the above-described range is advantageous for improving the high-speed charging performance of the battery.

[0040] In some embodiments, the positive electrode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a high-speed ion conductor material, and the second coating layer comprises a carbon material; the first coating layer is provided between a lithium-containing phosphate and the second coating layer; the carbon material generally has excellent adhesive performance, and in the above embodiments, the second coating layer containing the carbon material is provided on the outer surface of the first positive electrode active material to enhance the adhesion between the first positive electrode active material and the current collector, thereby reducing the risk of the first positive electrode active material peeling off during battery use and improving the service life of the battery.

[0041] In some embodiments, the positive electrode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a high-speed ion conductor material, the second coating layer comprises a carbon material, and the second coating layer is provided between the lithium-containing phosphate and the first coating layer. In the above embodiments, during the lithium ion transfer process, the lithium ions first pass through the first coating layer composed of the high-speed ion conductor material, then enter the second coating layer, and finally diffuse into the lithium-containing phosphate, thereby being advantageous for accelerating the movement speed of lithium ions within the first positive electrode active material and improving the high-speed charging performance of the battery. Additionally, the carbon material of the second coating layer has good electrical conductivity and can accelerate electron transport by forming a continuous electrically conductive network between the lithium-containing phosphate and the first coating layer, thereby further improving the high-speed charging performance of the battery.

[0042] In some embodiments, the high-speed ion conductor material comprises a compound represented by formula (II):

[0043] Li 3-b Fe 2-b M 2 b (PO4)3 Equation (II); in Equation (II), M 2 is selected from at least one of Ti, Zr, Hf, Ge, and Sn, and 0≤b≤1. The above-described high-speed ion conductor material has excellent ion conductivity, and selecting and using the above-described high-speed ion conductor material is advantageous for further improving the high-speed charging performance of the battery.

[0044] In some embodiments, the mass ratio of carbon elements in the first positive electrode active material is 1% to 1.5%. This makes it advantageous for the first positive electrode active material to achieve a high capacity and, furthermore, for the secondary battery to achieve a high energy density, while on the other hand, it makes it advantageous for improving the electron conductivity of the first positive electrode active material and, furthermore, for improving the fast charging performance of the lithium-ion secondary battery.

[0045] In some embodiments, the BET specific surface area of ​​the first positive active material is 12 m² 2 / g to 16m 2 / g; thereby, the surface of the first positive electrode active material can provide more lithium ion insertion and extraction pathways. During the fast charging process, lithium ions can be inserted into the first positive electrode active material more quickly through these pathways, and the fast charging performance of the battery is improved by reducing the transport distance and resistance of the lithium ions.

[0046] In some embodiments, the tap density of the first positive active material is 0.8 g / cm³ 3 Up to 1.3 g / cm² 3 And; thereby, it is advantageous for the anode film layer to form a pore structure rich in this, and it is possible to ensure that the battery has superior high-speed charging performance.

[0047] In some embodiments, the volume average particle size Dv50 of the first positive active material is 1 μm to 3 μm, which is advantageous for forming a rich porous channel structure between the particles of the first positive active material, thereby improving lithium ion and electron transport performance in the positive film layer and further improving the mechanical performance of the secondary battery.

[0048] In some embodiments, the compaction density of the first positive active material under 50,000 N is 2.4 g / cm³ 3 Up to 2.6 g / cm² 3 This makes the contact between the first anode materials tighter, which is advantageous for improving the energy density of the battery.

[0049] 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. Since the lithium transition metal oxide has a higher specific capacity, selecting and using the lithium transition metal oxide as the second positive electrode active material is advantageous for further improving the energy density of the secondary battery.

[0050] In some embodiments, the mass ratio of the first positive active material and the second positive active material is (99 to 90):(1 to 10). This is advantageous for considering both the service life and energy density of the secondary battery.

[0051] In some embodiments, the thickness of the positive film layer provided on a single side of the positive current collector is 100 μm to 200 μm, and thus the positive film layer is advantageous for considering high capacity, high lithium ion and electron transport performance, and furthermore, the secondary battery is advantageous for considering high energy density and fast charging performance.

[0052] In some embodiments, the coating weight of the anode film layer provided on a single side of the anode current collector is 200 mg / 1540.25 mm 2 Up to 400 mg / 1540.25 mm 2 And; thereby, it is advantageous to improve the amount of lithium ions released by the anode film layer per unit area, and furthermore, improves the energy density of the battery.

[0053] In some embodiments, the compaction density of the anode film layer is 2 g / cm³ 3 Up to 3g / cm² 3 This makes it advantageous for the anode film layer to maintain an excellent pore structure, reduces the degree of bending of the anode film layer, and shortens the lithium ion transport path, thereby improving the fast charging performance and lifespan performance of the battery, while also considering energy density.

[0054] In some embodiments, the thickness of the positive current collector is 10 μm to 18 μm. This is advantageous for the battery to achieve high energy density on one hand, and on the other hand, to reduce the risk of cracking in the positive current collector, and further extends the service life of the battery.

[0055] In some embodiments, the anode film layer further comprises an anode dispersant, and the anode dispersant comprises at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, and carboxymethyl cellulose sodium. The anode dispersant described above has good flexibility and elasticity and can disperse the stress received by the anode active material during the compression process, and by selecting and using the anode dispersant described above, it is advantageous to achieve a high compaction density in the anode film layer and further improve the energy density of the battery.

[0056] In some embodiments, the mass ratio of the anode dispersant to the anode film layer is 0.3% to 5%. This is advantageous for the battery to achieve high energy density.

[0057] In some embodiments, the secondary battery further comprises an electrolyte, and the electrolyte further 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone; The electrolyte salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalate)borate, lithium bis(oxalate)borate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0058] In some embodiments, the electrolyte further comprises an additive, and the additive comprises at least one of barium sulfate, polytrifluoroethyl methacrylate, acyclic sulfate, tricyclic sulfate, tris(trimethylsilyl)phosphate, and vinylene carbonate. The above-described additive preferentially causes an electrochemical reduction reaction on the surface of the negative electrode sheet over solvent molecules in the electrolyte, thereby forming a dense and stable SEI film layer, which is advantageous for suppressing the growth of lithium dendrites and improving the safety performance of the battery.

[0059] In some embodiments, the mass ratio of the additive in the electrolyte is 1% to 10%. This is advantageous for forming an SEI film of appropriate thickness on the electrode surface, while on the one hand, it is advantageous for suppressing the growth of lithium dendrites and improving the safety performance of the battery. On the other hand, it is advantageous for considering the transport resistance of lithium ions in the negative electrode sheet, thereby also considering the fast charging performance of the battery.

[0060] In some embodiments, the electrical conductivity of the electrolyte is 10 mS / cm to 18.5 mS / cm. This is advantageous for reducing the internal resistance of the battery and reduces energy consumption caused by resistance during the charging and discharging process.

[0061] A second aspect of the present application provides an electric device, said electric device comprising a secondary battery as described in the first aspect of the present application. Brief explanation of the drawing

[0062] FIG. 1 is a schematic diagram of a secondary battery according to one embodiment of the present application. FIG. 2 is an exploded view of a secondary battery according to one embodiment of the present application shown in FIG. 1. FIG. 3 is a schematic diagram of a battery module according to one embodiment of the present application. FIG. 4 is a schematic diagram of a battery pack according to one embodiment of the present application. FIG. 5 is an exploded view of a battery pack according to one embodiment of the present application shown in FIG. 4. FIG. 6 is a schematic diagram of an electric device using a secondary battery as a power source according to one embodiment of the present application. FIG. 7 is a scanning electron microscope (SEM) image of a separator according to Example 1 of the present application. Specific details for implementing the invention

[0063] Hereinafter, embodiments of a secondary battery and an electric device according to the present application will be specifically disclosed with appropriate reference to the detailed description of the attached drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of known matters and repetitive descriptions of structures that are actually identical may be omitted. This is intended to prevent the following description from becoming unnecessarily long and to enable those skilled in the art to understand it easily. Furthermore, the attached drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the present application.

[0064] The “range” disclosed in this application is limited in the form of lower and upper limits, and a given range is limited by selecting one lower limit and one upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. A range limited in this way may include or not include end values ​​and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also expected. Additionally, if minimum range values ​​1 and 2 are listed and maximum range values ​​3, 4 and 5 are listed, ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 may all be expected. In this application, unless otherwise stated, the numerical range “a to b” represents an abbreviated expression of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0 to 5” indicates that all real numbers between “0 to 5” are listed in this specification, and “0 to 5” is merely an abbreviated expression of a combination of such numbers. Additionally, if a parameter is represented as an integer ≥ 2, this corresponds to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments of the present application and selectable embodiments may be combined with one another to form a new technical solution.

[0066] Unless otherwise specified, all technical features and selectable technical features of the present application may be combined with one another to form a new technical solution.

[0067] Unless otherwise specified, all steps of the present application may proceed sequentially or randomly, preferably sequentially. For example, the expression “the method comprises steps (a) and (b)” indicates that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially. For example, the expression “the method may further comprise step (c)” indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b), and (c), steps (a), (c), and (b), and steps (c), (a), and (b), etc.

[0068] Unless otherwise specified, "includes" and "comprehensively" as used in this application mean open or closed. For example, "includes" and "comprehensively" may mean that other unlisted components may be included or comprehensive, or that only the listed components may be included or comprehensive.

[0069] Recently, as the scope of applications for secondary batteries gradually expands, they are being widely applied in various fields, including energy storage power systems such as hydroelectric, thermal, wind, and solar power plants, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.

[0070] As secondary batteries have made rapid progress, demands regarding aspects such as energy density and safety performance of secondary batteries have increased in actual applications.

[0071] In related technologies, the energy density of a battery is generally improved by increasing the compaction density of the membrane layer. However, this method has a significant drawback: while increasing compaction density, it also increases the amount of heat released from within the battery, which subsequently leads to a deterioration in the battery's safety performance. For example, separators are generally manufactured from polymeric materials such as polyethylene (PE) and polypropylene (PP). The molecules of these polymeric materials consist of long, chain-shaped molecular chains. At room temperature, the molecular chains are in a relatively stable state, and a certain force exists between them, allowing the separator to maintain a stable shape. When the temperature rises, the molecules gain more energy, the thermal motion of the molecular chains intensifies, and the spacing between the chains increases, resulting in a more disordered arrangement. Due to these changes in the motion and arrangement of the molecular chains, the separator undergoes a macroscopic size change, specifically thermal shrinkage. This thermal shrinkage of the separator causes the positive and negative sheets to overlap, thereby degrading the battery's safety performance. Therefore, considering both the energy density and safety performance of batteries has become an urgent technical challenge that needs to be addressed.

[0072] To solve the aforementioned technical problem, the present application provides a secondary battery and an electric device. The secondary battery considers both energy density and safety performance.

[0073] A first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive current collector and a positive film layer provided on at least one surface of the positive current collector, and the compaction density of the positive film layer is 2.0 g / cm³ 3 Up to 3.0 g / cm² 3 The cathode sheet comprises a cathode current collector and a cathode film layer located on at least one surface of the cathode current collector, and the compaction density of the cathode film layer is 1.4 g / cm³ 3 Up to 1.85 g / cm²3 The separator includes a base film, and the thickness of the base film is 4 μm to 12 μm.

[0074] In this application, the compaction density of the anode film layer is 2.0 g / cm² 3 Up to 3.0 g / cm² 3 Controlled by and the compaction density of the cathode film layer is 1.4 g / cm³ 3 Up to 1.85 g / cm² 3 By controlling it, the battery is advantageous for achieving high energy density.

[0075] The aforementioned compaction density helps in the close arrangement of electrode material particles and improves the energy density of the battery. However, at the same time, it hinders the penetration of the electrolyte and may lead to an increase in battery resistance, and furthermore, an excess amount of heat is generated during the discharge process, which affects the safety performance of the battery.

[0076] Accordingly, the present application uses a base film having a thickness of 4 μm to 12 μm, thereby reducing the impact on battery safety performance caused by the base film being excessively thin (less than 4 μm), while simultaneously reducing the adverse impact on battery energy density caused by the base film being excessively thick (more than 12 μm). The battery can have improved battery safety performance and simultaneously secure high energy density. Specifically, a base film with a thickness within the aforementioned range can maintain structural stability at high temperatures and effectively reduce the risk of short circuits between the positive and negative electrodes. In particular, during battery thermal runaway, a base film with a stable structure can suppress the occurrence of side reactions through physical isolation, thereby lowering the maximum temperature during battery thermal runaway, reducing the risk of thermal diffusion, and improving the safety performance of the battery. Furthermore, since the base film thickness is within the aforementioned range, it is advantageous to reduce the adverse impact of the base film on battery energy density, thereby making it advantageous for the battery to maintain high energy density. The base film is provided with nanopores, and the average pore size of the nanopores is 10 nm to 300 nm. By using a base film in which the average pore size of the nanopores is within the aforementioned range, it helps to improve the mobility of lithium ions, while also being advantageous for considering the growth of lithium dendrites, thereby further improving the safety performance of the battery.

[0077] In this application, "compaction density" refers to the mass per unit volume of active materials (positive and negative active materials) after compression under constant pressure conditions. In battery systems, this is primarily used to describe the degree of tightness between the positive and negative film layers and reflects the loading amount of active material in the electrode film layers per unit volume.

[0078] In this application, compaction density may be tested by methods known in the art. The sheets to be tested (anode sheets, cathode sheets) may be sheets obtained by manufacturing, or sheets obtained by disassembling a battery. For example, in the case of an anode sheet obtained by disassembling a battery, the anode sheet has an area of ​​1540.25 mm² 2 The circular piece was cut, the mass m1 of the circular piece was weighed, and the thickness of the circular piece was measured multiple times at various locations using a micrometer, the average value was taken, and recorded as d1. Then, the anode film layer prepared on one side of the circular piece was removed, the mass m2 of the circular piece was weighed, and the thickness of the circular piece was measured multiple times at various locations using a micrometer, the average value was taken, and recorded as d2. The compaction density of the anode film layer was calculated as (m1-m2) / (d1-d2).

[0079] In this application, the compaction density of the anode film layer is 2 g / cm³ 3 Up to 3g / cm² 3 is. For example, the compaction density of the anode film layer is 2 g / cm³. 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.60g / cm 3 , 2.7 / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3 Or it may be a value between the ranges consisting of any two of these values. Optionally, the compaction density of the anode film layer is 2.3 g / cm³ 3 Up to 2.5 g / cm² 3 am.

[0080] In this application, the compaction density of the cathode film layer is 1.4 g / cm³ 3 Up to 1.85 g / cm² 3is. For example, the compaction density of the cathode film layer is 1.4 g / cm³. 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.62g / cm 3 , 1.64g / cm 3 , 1.65g / cm 3 , 1.85g / cm 3 Or it may be a value between a range consisting of any two of these numbers.

[0081] In the present application, the thickness of the base film can be tested using a micrometer or a micrometer with an accuracy of 0.1 μm. For example, the thickness was measured multiple times at various locations of the base film using a micrometer, and the average value was taken and recorded as the thickness of the base film.

[0082] In the present application, the thickness of the base film is 4 μm to 12 μm. For example, the thickness of the base film is a value between a range of 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any two of these values. Optionally, the thickness of the base film is 5 μm to 9 μm.

[0083] In this application, the average pore size can be tested by methods known in the art. The separator to be tested may be a separator obtained by manufacturing, or a separator obtained by disassembling a battery. For example, a separator (base film) may be obtained by disassembling a battery, and the average pore size of the base film may be tested by using a pore tester (model: PMI Porometer) and referring to GB / T 21650.2-2008.

[0084] For example, the average pore size of the nanopore is a value between a range consisting of 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 any two of these values. The term “secondary battery” as used herein means a battery cell, a battery module, or a battery pack. Each will be described below. Unless otherwise noted, the battery referred to in this application refers to a secondary battery.

[0085] Under general circumstances, a secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, lithium ions are reciprocally inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to transport ions between the positive electrode sheet and the negative electrode sheet. The separator is positioned between the positive electrode sheet and the negative electrode sheet and primarily functions to prevent short circuits between the positive and negative electrodes while simultaneously allowing ions to pass through.

[0086] separator

[0087] The present application does not specifically limit the type of separator, and any known separator with a porous structure having good chemical stability and mechanical stability may be selected and used.

[0088] In some embodiments, the material of the separator may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and molyvinylidene difluoride. The separator may be a single-layer thin film or a multi-layer composite thin film, and is not particularly limited. When the separator is a multi-layer composite thin film, the materials of each layer may be the same or different from each other, and are not particularly limited.

[0089] In some embodiments, the base film comprises at least one of a polyethylene base film, a polypropylene base film, a polyethylene-polypropylene composite base film, a polyethylene nonwoven base film, a polypropylene nonwoven base film, a polypropylene-polyethylene-polypropylene composite base film, a polyimide base film, a polyimide nonwoven base film, a polytetrafluoroethylene base film, a polytetrafluoroethylene nonwoven base film, a polyvinyl chloride base film, or a polyvinyl chloride nonwoven base film.

[0090] In some embodiments, the porosity of the base film is 20% to 70%, and using a base film with a porosity within the range described above helps to improve the mobility of lithium ions while also being advantageous for considering the growth of lithium dendrites, thereby further improving the safety performance of the battery. For example, the porosity of the base film is a value between a range consisting of 20%, 30%, 40%, 50%, 60%, 70%, or any two of these values. Optionally, the porosity of the base film is 35% to 42%.

[0091] In some embodiments, the separator further comprises a coating layer provided on at least one side of a base film, wherein the coating layer comprises heat-resistant particles, and the heat-resistant particles are interwoven to form a porous structure. Compared to a coating layer without a porous structure, in the above embodiment, the heat-resistant particles are interwoven to form a porous structure, which is advantageous for reducing the inhibition of ion transport by the coating layer, thereby improving ion transport efficiency. Additionally, the coating layer comprises heat-resistant particles, and the volume of the heat-resistant particles changes little with temperature. By providing a coating layer containing heat-resistant particles on the surface of the base film, it is advantageous for suppressing the thermal shrinkage rate of the base film, thereby further reducing the risk of a negative electrode short circuit and improving the safety performance of the battery.

[0092] In some embodiments, the thickness of the coating layer provided on one side of the base film is 0.011 μm to 3 μm. By selecting and using a coating layer with a thickness within the above-described range, on the one hand, it is advantageous for the battery to achieve high energy density, and on the other hand, the coating layer is advantageous for better suppressing the thermal shrinkage rate of the base film, thereby further improving the safety performance of the battery. For example, the thickness of the coating layer is a value between a range consisting of 0.011 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, 3 μm, or any two of these values.

[0093] In some embodiments, the average particle size of the heat-resistant particles is 5 nm to 185 nm. Heat-resistant particles with an average particle size of 5 nm to 185 nm can form a coating layer with a stable support network structure and support the base film while simultaneously suppressing thermal shrinkage of the base film, thereby improving the safety performance of the battery. For example, the average particle size of the heat-resistant particles is a value between a range consisting of 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, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 185 nm, or any two of these values.

[0094] In some embodiments, the particle areal density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 Up to 2.5 mg / 1540.25 cm 2By controlling the particle areal density within the aforementioned range, it is advantageous for the battery to achieve high energy density, while simultaneously being advantageous for the heat-resistant particles to perform the function of suppressing thermal shrinkage of the base film, thereby improving the safety performance of the battery. For example, the particle areal density of the heat-resistant particles is 0.5 mg / 1540.25 cm² 2 , 0.6mg / 1540.25cm 2 , 0.7mg / 1540.25cm 2 , 0.8mg / 1540.25cm 2 , 0.9mg / 1540.25cm 2 , 1mg / 1540.25cm 2 , 1.1mg / 1540.25cm 2 , 1.2mg / 1540.25cm 2 , 1.25mg / 1540.25cm 2 , 1.3mg / 1540.25cm 2 , 1.4mg / 1540.25cm 2 , 1.5mg / 1540.25cm 2 , 1.6mg / 1540.25cm 2 , 1.7mg / 1540.25cm 2 , 1.8mg / 1540.25cm 2 , 1.85mg / 1540.25cm 2 Or a value between the ranges consisting of any two of these values. Optionally, the particle areal density of the heat-resistant particles is 1.25 mg / 1540.25 cm 2 Up to 1.85 mg / 1540.25 cm 2 am.

[0095] 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 the above implementation, the first heat-resistant particles are distributed on the surface of the base film, and the first heat-resistant particles can directly suppress the thermal shrinkage of the base film, which is advantageous for further improving the safety performance of the battery and can also be taken into account for the energy density of the battery.

[0096] In some embodiments, the heat-resistant particles comprise a first heat-resistant particle and a second heat-resistant particle; wherein the first heat-resistant particle is distributed on the surface of the base film, and the second heat-resistant particle is laminated on one side away from the first heat-resistant particle. In the above embodiment, the first heat-resistant particle and the second heat-resistant particle are laminated in the thickness direction of the base film, which is advantageous for forming a thicker coating layer, and the thicker coating layer acts as a more effective physical barrier, which can reduce chemical erosion of the electrolyte on the base film and simultaneously buffer friction of the sheet (anode sheet, cathode sheet) against the base film, thereby further improving the safety performance of the battery.

[0097] In some embodiments, the heat-resistant particles comprise inorganic particles and adhesive particles. In the above embodiment, the adhesive particles act as a mediator to tightly bind the inorganic particles. This allows the inorganic particles to form a single stable overall structure, thereby improving the mechanical strength and stability of the coating layer and better suppressing thermal shrinkage of the base film.

[0098] In some embodiments, the first glass transition temperature of the adhesive particles is 30°C to 75°C; and / or, the second glass transition temperature of the adhesive particles is -10°C to 25°C.

[0099] In some embodiments, the adhesive particles comprise one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, or polystyrene ester.

[0100] In some embodiments, the heat-resistant particles comprise inorganic particles and an adhesive layer provided on at least a portion of the surface of the inorganic particles. In the above embodiment, the adhesive layer is provided on the surface of the inorganic particles, which is advantageous for improving the bonding strength between the inorganic particles and the base film, reducing the risk of the inorganic particles peeling off, and improving the safety performance and service life of the battery.

[0101] In some embodiments, the first glass transition temperature of the adhesive layer is 30°C to 75°C; and / or, the second glass transition temperature of the adhesive layer is -10°C to 25°C.

[0102] In some embodiments, the adhesive layer comprises one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyurethane, or polystyrene ester.

[0103] In some embodiments, the inorganic particles comprise 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-described material changes little with temperature and is advantageous for use as inorganic particles to further suppress thermal shrinkage of the base film, thereby further improving the safety performance of the battery.

[0104] In some embodiments, the mass ratio of inorganic particles in the coating layer is 5% to 30%. By controlling the mass ratio of inorganic particles within the above-described range, it is advantageous for the inorganic particles to form a heat-resistant framework structure in the coating layer, effectively suppress thermal shrinkage of the coating layer, and improve the safety performance of the battery, while also reducing the risk of inorganic particles detaching. For example, the mass ratio of inorganic particles is a value between a range consisting of 5%, 10%, 15%, 20%, 25%, 30%, or any two of these values.

[0105] In this application, the mass ratio of inorganic particles can be tested by methods known in the art. The separator to be tested may be a separator obtained by manufacturing, or a separator obtained by disassembling a battery. For example, a separator is obtained by disassembling a battery, the coating layer is separated from the base film to collect the coating layer, and the mass m3 of the coating layer is weighed. Adhesive particles or the adhesive layer are dissolved using a suitable solvent, and then the inorganic particles are filtered to weigh the mass m4 of the inorganic particles, and m4 / m3 is the mass ratio of the inorganic particles.

[0106] cathode sheet

[0107] A first aspect of the present application provides a secondary battery, wherein the secondary battery comprises a negative electrode sheet, the negative electrode sheet comprises a negative current collector and a negative film layer located on at least one surface of the negative current collector, the negative film layer comprises a first film layer and a second film layer disposed between the first film layer and the negative current collector, the first film layer comprises a first negative active material, the first negative active material comprises a first graphite material, and I of the first graphite material D / I G is 0.4 to 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 I of the second graphite material D / I G is 0.05 to 0.2; where I D 1350±50cm in the Raman spectrum -1 Indicates the D peak intensity at the position, and I G 1580±50cm in the Raman spectrum -1 It indicates the G peak intensity of the location.

[0108] I of the first graphite material used in this application D / I GThe value is 0.4 to 0.9, indicating that a large number of defects exist on the surface of the first graphite material, and these defects can serve as additional active sites for lithium ion insertion. Providing this first graphite material with many surface defects on the outer layer (first film layer) of the cathode sheet is advantageous for increasing the possibility of contact between the additional active sites and the electrolyte, thereby improving the fast charging performance of the battery.

[0109] On this basis, as an inner layer (second film layer) of the cathode sheet, I D / I G A second graphite material having a value of 0.05 to 0.2 is used, and the second graphite material has few surface defects and a relatively complete structure, which is advantageous for reducing irreversible loss of lithium ions and thereby extending the service life of the battery.

[0110] In this application, the morphology of the cathode sheet can be tested by methods known in the art. The cathode sheet to be tested may be a cathode sheet obtained by manufacturing, or a cathode sheet obtained by disassembling a battery. Below, the testing process will be described using the latter as an example. Specifically, a battery is disassembled to obtain a cathode sheet, the cathode sheet is placed in a sample holder and locked in place, the cross-section of the cathode sheet is cut using an argon ion cross-section polisher (e.g., the IB-09010 CP type argon ion cross-section polisher of JEOL, Japan), and a cross-section SEM image of the cathode sheet is obtained using a scanning electron microscope (HR-TEM Talos F200). From the cross-section SEM image, it can be seen that the cathode sheet comprises a cathode current collector, a second film layer provided on the surface of the cathode current collector, and a first film layer provided on the surface of the second film layer.

[0111] In the present application, I of the graphite material (first graphite material, second graphite material). D / I GThe value can be tested by methods known in the art. The graphite material to be tested may be a graphite material obtained by manufacturing, or a graphite material obtained by disassembling a battery. Below, the test process will be explained using the latter as an example. Specifically, a negative electrode sheet is obtained by disassembling a battery, a first film layer is scraped off with a scraper, the first film layer is dissolved using a suitable solvent, and then the first graphite material is filtered to obtain the I of the first graphite material D / I G Test the second film layer with a scraper, dissolve the second film layer using a suitable solvent, and then filter the second graphite material to test the I of the second graphite material. D / I G Test the following. It should be noted that a clear interface may exist at the boundary location between the first film layer and the second film layer, or a clear interface may not exist. To reduce sampling error, the sampling area of ​​the second film layer is defined as a position extended 2.5 μm in the direction of the cathode film layer from the surface of the cathode film layer approaching the current collector; and the sampling area of ​​the first film layer is defined as a position extended 2.5 μm in the direction of the cathode film layer from the surface of the cathode film layer away from the current collector.

[0112] The test conditions are as follows: the excitation wavelength is 532 nm, the diffraction grating is 600 scales, the objective lens is 50x magnification, the integration time is 10 s, the accumulation count is 3, and surface scanning is performed to obtain the D peak and G peak intensities at 100 points, and the I of 100 points D / I G Calculate, and the I of each of the 30 maximum and minimum values D / I G Remove it, and the average value of the remaining 40 points is the material's I D / I G The test instrument can be the Horiba LabRAM HR800 Raman spectrometer.

[0113] In the present application, I of the first graphite material D / I G is 0.4 to 0.9. For example, I of the first graphite material D / I G is a value between the range of 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or any two numbers, but is not limited thereto.

[0114] In the present application, I of the second graphite material D / I G is 0.05 to 0.2. For example, I of the second graphite material D / I G is a value between the range of 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 any two numbers, but is not limited thereto.

[0115] As an example, the cathode current collector has two opposing surfaces in its thickness direction, and the cathode film layer is provided between any one or both of the two opposing surfaces of the cathode current collector.

[0116] In some embodiments, the volume average particle size of the first graphite material is 9.2 μm to 15.5 μm. This is advantageous for forming a rich porous channel 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 mechanical performance of the secondary battery. For example, the volume average particle size Dv50 of the first graphite material is a value between a range consisting of 9.2 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 15.5 μm, or any two numerical values, but is not limited thereto.

[0117] In some embodiments, the volume average particle size Dv50 of the second graphite material is 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, it is advantageous for improving the abundant porous channel structure between the particles of the second graphite material, improving the lithium ion and electron transport performance in the negative film layer, and further improving the mechanical performance of the secondary battery. For example, the volume average particle size Dv50 of the second graphite material is a value between a range consisting of 16.3 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25.5 μm, or any two numerical values, but is not limited thereto.

[0118] In this application, the volume distribution particle size Dv50 of the material represents the particle size corresponding when the cumulative volume percentage of the material reaches 50%, and can be measured using instruments and methods known in the art. For example, with reference to GB / T 19077-2016, the test is performed using a laser particle size analyzer. The test instrument may be a Mastersizer 3000 type laser particle size analyzer from Malvern Instruments Ltd., UK.

[0119] In some embodiments, the BET specific surface area of ​​the first graphite material is 0.3 m 2 / g to 3m 2 / g. When the BET specific surface area of ​​the first graphite material is within the range described above, the surface of the first graphite material can provide more lithium ion insertion and extraction pathways. During the fast charging process, lithium ions can be inserted into the first graphite material more rapidly through these pathways, improving the fast charging performance of the battery by reducing the transport distance and resistance of the lithium ions. For example, the BET specific surface area of ​​the first graphite material is 0.3m² 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 It is a value between / g or any two numeric values, but is not limited thereto.

[0120] In some embodiments, the BET specific surface area of ​​the second graphite material is 0.5 m 2 / g to 5m 2 / g. When the BET specific surface area of ​​the second graphite material is within the range described above, the surface of the second graphite material can provide more lithium ion insertion and extraction pathways. During the fast charging process, lithium ions can be inserted into the second graphite material more rapidly through these pathways, improving the fast charging performance of the battery by reducing the transport distance and resistance of the lithium ions. For example, the BET specific surface area of ​​the second graphite material is 0.5m² 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, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 5m 2 It is a value between / g or any two numeric values, but is not limited thereto.

[0121] In this application, the specific surface area BET of the materials (second graphite material, first graphite material, first cathode active material) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, with reference to GB / T 19587-2017, the test is performed using the nitrogen adsorption specific surface area analysis test method and calculated using the BET (Brunauer Emmett Teller) method. The specific surface area pore size analyzer Tri-Star 3020 from Micromeritics, USA, can be used as the test instrument.

[0122] In some embodiments, the tap density of the first graphite material is 0.7 g / cm³ 3 Up to 1.6 g / cm² 3 The tap density of the first graphite material is within the range described above, which is advantageous for forming a porous structure rich in the first film layer, and ensures that the battery has superior high-speed charging performance. For example, the tap density of the first graphite material is 0.7 g / cm³ 3 , 0.8g / cm3, 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 it is a value between a range consisting of any two numerical values, but is not limited thereto.

[0123] In some embodiments, the tap density of the second graphite material is 0.8 g / cm³ 3 Up to 1.5 g / cm² 3 The tap density of the second graphite material is within the range described above, which is advantageous because the second graphite material can be tightly laminated within the second film layer and can accommodate more of the second graphite material (active material) in the second film layer, and furthermore, improves the energy density of the battery. For example, the tap density of the second graphite material is 0.8 g / cm³3 , 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 Or it is a value between a range consisting of any two numerical values, but is not limited thereto.

[0124] In this application, the tap density of the materials (second graphite material, first graphite material, first cathode active material) has the meaning known in the art and can be measured using instruments and methods known in the art. For example, with reference to GB / T 5162-2006, it can be measured using a powder tap density tester. The Dandong Baite BT-301 may be used as the test instrument, and the test parameters are as follows: vibration frequency 250±15 times / min, amplitude 3±0.2 mm, number of vibrations 5000 times, graduated cylinder 25 mL.

[0125] 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 amorphous carbon has a relatively loose structure and has a rich pore structure. These pores can provide more diffusion pathways for lithium ions and shorten the diffusion path of lithium ions in the electrode material. By providing amorphous carbon on the surface of the first graphite material, lithium ions can pass through the negative electrode coating layer more quickly and reach the interior of the first graphite material, thereby improving the high-speed charging performance of the battery.

[0126] In the present application, a cathode coating layer on the surface of a first graphite material can be shown using TEM. Microstructural morphology information of the first cathode active material is obtained using SEM. As a result of TEM observation, the first graphite material has a periodically repeating crystal lattice structure. If a regular crystal lattice structure does not exist on the surface of the first graphite material, it indicates that amorphous carbon is provided on the surface of the first graphite material.

[0127] In some embodiments, the thickness of the negative electrode coating layer is 10 nm to 100 nm. Since the thickness of the negative electrode coating layer is within the range described above, it is advantageous for the secondary battery to consider both fast charging performance and energy density. For example, the thickness of the negative electrode coating layer is a value between a range consisting of 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any two numerical values, but is not limited thereto.

[0128] In the present application, the thickness of the cathode coating layer can be characterized by combining a scanning electron microscope (SEM) and a focused ion beam (FIB). A sample (first cathode active material) is fixed to a sample stage, and a flat cross-section is cut from the sample surface using an FIB. Then, the cross-section is imaged with an SEM, and the thickness is determined by measuring the width of the cathode coating layer in the image.

[0129] 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 over multiple charge-discharge cycles, reduce the rate of decay of battery capacity, and extend the service life of the battery. The first graphite material can improve the fast charging performance of the battery. In the above embodiments, the second graphite material and the first graphite material are disposed in the second film layer, which is advantageous for improving the fast charging performance of the battery.

[0130] In the present application, the second film layer comprises a second graphite material and a first graphite material, and can be tested by a method known in the art. The cathode sheet to be tested may be a cathode sheet obtained by manufacturing, or a cathode sheet obtained by disassembling a battery. Specifically, the cathode sheet is placed in a sample holder and locked in place, and the cross-section of the cathode sheet is cut using an argon ion cross-section polisher (e.g., the IB-09010 CP type argon ion cross-section polisher of JEOL, Japan). A cross-sectional SEM image of the cathode sheet is obtained using a scanning electron microscope (HR-TEM Talos F200). From the cross-sectional SEM image, it can be seen that the cathode sheet comprises a cathode current collector, a second film layer provided on the surface of the cathode current collector, and a first film layer provided on the surface of the second film layer. The second film layer comprises a large particle material and a small particle material. Here, the large particle material is the second graphite material, and the small particle material is the first graphite material.

[0131] In some embodiments, the mass ratio of the second graphite material to the first graphite material in the second film layer is (3 to 5):(5 to 7). By controlling the mass ratio of the second graphite material to the first graphite material in the second film layer within the range described above, it is advantageous to further consider the improvement of the battery's fast charging performance and service life. For example, the mass ratio of the second graphite material to the first graphite material in the second film layer is a value between the ranges of 5:5, 4:6, 3:7, or any two values, but is not limited thereto.

[0132] In the present application, the mass ratio of the second graphite material and the first graphite material in the second film layer can be tested by a method known in the art. The cathode sheet to be tested may be a cathode sheet obtained by manufacturing, or a cathode sheet obtained by disassembling a battery. Specifically, a battery is disassembled to obtain a cathode sheet, and the first film layer is scraped off with a scraper to expose the second film layer. The second film layer is removed with a scraper and the second film layer is collected. The second film layer is dissolved using a suitable solvent and filtered to obtain a mixture of the second graphite material and the first graphite material, and the two are separated using the difference in particle size between the second graphite material and the first graphite material, and the mass of the second graphite material and the mass of the first graphite material are weighed, and furthermore, the mass ratio of the second graphite material and the first graphite material in the second film layer is obtained.

[0133] 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 to 5):(5 to 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-described range, it is advantageous to further consider improvements in the high-speed charging performance and service life of the battery. For example, the ratio of the average thickness of the first film layer to the average thickness of the second film layer is a value between a range consisting of 5:5, 4:6, 3:7, or any two numerical values, but is not limited thereto.

[0134] 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 cathode sheet to be tested may be a cathode sheet obtained by manufacturing, or a cathode sheet obtained by disassembling a battery. Specifically, a cross-sectional SEM image of the cathode sheet is obtained using a scanning electron microscope (HR-TEM Talos F200). From the cross-sectional SEM image, it can be clearly seen that the cathode sheet is composed of a cathode current collector, a second film layer located on the surface of the current collector, and a first film layer provided on the surface of the second film layer. Then, three sampling points are selected from the first film layer and the second film layer, respectively, and the thickness of the film layer at each sampling point is measured using image analysis software. The average value of the thickness values ​​from the four sampling points of the first film layer is taken to obtain the average thickness of the first film layer; and the average thickness of the second film layer is obtained in the same way. Finally, the ratio of the average thicknesses of the two is obtained through calculation, and the ratio of the average thickness of the first film layer to the average thickness of the second film layer can be accurately obtained.

[0135] In some embodiments, the first film layer further comprises a first binder, and the first binder comprises at least one of styrene-butadiene rubber, styrene-polybutadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, or carboxymethyl chitosan, and the viscosity of the above-described material is high, and by selecting and using the above-described material as the first binder, the risk of the first film layer peeling off and separating from the second film layer can be reduced, thereby being advantageous for further improving the service life of the secondary battery.

[0136] In some embodiments, the first binder comprises at least one of styrene-butadiene rubber, lithium polyacrylate, and polyacrylate.

[0137] Styrene-butadiene rubber has good flexibility and elasticity, and can disperse the stress received by the first negative electrode active material during the compression process during the electrode charging and discharging process, thereby enabling the first negative electrode active material to withstand greater pressure, and by selecting and using styrene-butadiene rubber as the first dispersant, it is advantageous to achieve a high compaction density in the first film layer and further improve the energy density of the battery.

[0138] Lithium polyacrylate has high ionic conductivity and is advantageous for use as a first binder to improve the fast charging performance of the battery.

[0139] Polyacrylate improves the compressive elasticity of the first cathode active material and can reduce the adverse effects on the mechanical performance of the cathode sheet during compression, thereby improving the high-speed charging performance of the battery.

[0140] In some embodiments, the second film layer further comprises a second binder, and the second binder comprises at least one of styrene-butadiene rubber, styrene-polybutadiene rubber, lithium polyacrylate, polyacrylate, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, or carboxymethyl chitosan. The viscosity of the second binder described above is high, and by selecting and using the material described above as the second binder, the risk of the second film layer peeling off from the negative current collector can be reduced, which is advantageous for further improving the service life of the secondary battery.

[0141] In some embodiments, the second binder comprises at least one of styrene-butadiene rubber, lithium polyacrylate, and polyacrylate. In the above embodiments, selecting and using the above-described material as the second binder is advantageous for considering the fast charging performance, service life, and energy density of the battery.

[0142] In some embodiments, the mass ratio of the first binder in the first film layer is 0.1% to 2%. By controlling the mass ratio of the first binder in the first film layer within the range described above, on the one hand, it is advantageous to prevent powdering and peeling of the first negative active material, thereby extending the service life of the battery. On the other hand, it is advantageous for the battery to achieve high energy density. For example, the mass ratio of the first binder in the first film layer is a value between a range consisting of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, or any two numerical values.

[0143] In some embodiments, the mass ratio of the second binder in the second film layer is 0.1% to 2%. By controlling the mass ratio of the second binder in the second film layer within the range described above, on the one hand, it is advantageous to prevent powdering and peeling of the second negative active material, thereby extending the service life of the battery. On the other hand, it is advantageous for the battery to achieve high energy density. For example, the mass ratio of the second binder in the second film layer is a value between a range consisting of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.5%, 2%, or any two numerical values.

[0144] In some embodiments, the first film layer further comprises a first dispersant, and the first dispersant comprises at least one polymer among lithium carboxymethyl cellulose and sodium carboxymethyl cellulose.

[0145] The aforementioned material has high ionic conductivity and is advantageous for selecting and using as a first dispersant to improve the high-speed charging performance of the battery.

[0146] 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-described material has high ionic conductivity and is advantageous for selecting and using as a second dispersant to improve the fast charging performance of the battery.

[0147] In some embodiments, the first dispersant comprises lithium carboxymethyl cellulose. The lithium carboxymethyl cellulose contains lithium ions, thereby compensating for the loss of active lithium ions caused by the formation of an SEI film during initial charging, and further improving the initial charging efficiency of the battery.

[0148] In some embodiments, the second dispersant comprises lithium carboxymethyl cellulose. The lithium carboxymethyl cellulose contains lithium ions, thereby compensating for the loss of active lithium ions caused by the formation of an SEI film during initial charging, and further improving the initial charging efficiency of the battery.

[0149] In some embodiments, the mass ratio of the first dispersant in the first film layer is 0.3% to 1.5%, and controlling the mass ratio of the first dispersant in the first film layer within the above-described range is advantageous for the battery to achieve high energy density. For example, the mass ratio of the first dispersant is a value between the ranges of 0.3%, 0.5%, 1%, 1.5%, or any two values.

[0150] In some embodiments, the mass ratio of the second dispersant in the second film layer is 0.3% to 1.5%. By controlling the mass ratio of the second dispersant in the second film layer within the range described above, it is advantageous for the battery to achieve high energy density. For example, the mass ratio of the second dispersant is a value between the ranges of 0.3%, 0.5%, 1%, 1.5%, or any two values.

[0151] In some embodiments, the first film layer further comprises a first conductive agent, and the first conductive agent comprises at least one of superconducting carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black, wherein the above-described material has good electrical conductivity performance, and it is advantageous to select and use the above-described material as the first conductive agent to further improve the fast charging performance of the battery. Optionally, the first conductive agent comprises carbon nanotubes and conductive carbon black, and it is advantageous to select and use the above-described material as the first conductive agent to further improve the fast charging performance of the battery.

[0152] In some embodiments, the second film layer further comprises a second conductive agent, and the second conductive agent comprises at least one of superconducting carbon, acetylene black, ketjen black, carbon dots, graphene, carbon nanofibers, carbon nanotubes, and conductive carbon black. The above-described materials have good electrical conductivity performance, and selecting and using the above-described materials as the second conductive agent is advantageous for further improving the high-speed charging performance of the battery. Optionally, the second conductive agent comprises carbon nanotubes and conductive carbon black.

[0153] In some embodiments, the mass ratio of the first conductive agent in the first film layer is 0.1% to 2%. Controlling the mass ratio of the first conductive agent in the first film layer within the above-described range is advantageous for improving the overall electrical conductivity of the first film layer, thereby further improving the high-speed charging performance of the secondary battery. For example, the mass ratio of the first conductive agent in the first film layer is a value between a range consisting of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, or any two numerical values.

[0154] In some embodiments, the mass ratio of the second conductive agent in the second film layer is 0.1% to 2%. Controlling the mass ratio of the second conductive agent in the second film layer within the above-described range is advantageous for improving the overall electrical conductivity of the second film layer, thereby further improving the high-speed charging performance of the secondary battery. For example, the mass ratio of the second conductive agent in the second film layer is a value between a range consisting of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, or any two numerical values.

[0155] In some embodiments, the thickness of the cathode film layer provided on a single side of the cathode current collector is 40 μm to 75 μm; by controlling the thickness of the cathode film layer within the above-described range, it is advantageous for the cathode film layer to have high capacity, high lithium-ion and electron transport performance, and furthermore, it is advantageous for the secondary battery to have high energy density and fast charging performance. For example, the thickness of the cathode film layer may be a value between a range consisting of 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, or any two of these values.

[0156] In some embodiments, the coating weight of the cathode film layer provided on a single side of the cathode current collector is 80 mg / 1540.25 mm 2 Up to 170 mg / 1540.25 mm 2 And; by controlling the coating weight of the cathode film layer within the aforementioned range, the quantity of lithium ions emitted by the cathode film layer per unit area can be improved, and furthermore, the energy density of the battery is improved. For example, the coating weight of the cathode film layer is 80 mg / 1540.25 mm 2 , 90mg / 1540.25mm 2 , 100mg / 1540.25mm 2 , 110mg / 1540.25mm 2 , 120mg / 1540.25mm 2 , 130mg / 1540.25mm2 , 140mg / 1540.25mm 2 , 150mg / 1540.25mm 2 , 160mg / 1540.25mm 2 , 170mg / 1540.25mm 2 Or it is a value between a range consisting of any two numbers.

[0157] In this application, the coating weight of the cathode film layer can be tested by a method known in the art. The cathode sheet to be tested may be a cathode sheet obtained by manufacturing, or a cathode sheet obtained by disassembling a battery. Specifically, a cathode sheet is obtained by disassembling a battery, and the cathode sheet has an area of ​​1540.25 mm² 2 The circular piece is cut, the mass m5 of the circular piece is weighed, and then the cathode film layer provided on one side of the circular piece is removed, the mass m6 of the circular piece is weighed, and the coating weight of the cathode film layer is calculated as m5-m6.

[0158] In some embodiments, the thickness of the negative current collector is 4 μm to 8 μm. Since the thickness of the negative current collector is within the above-described range, on the one hand, it is advantageous for the battery to achieve high energy density, on the other hand, it is advantageous for reducing the risk of cracking of the negative current collector, and furthermore, extends the service life of the battery. For example, the thickness of the negative current collector is a value between a range consisting of 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, or any two of these values.

[0159] In some embodiments, the negative current collector may use a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector is formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), etc.).

[0160] In some embodiments, the cathode film layer may optionally further include other auxiliary agents, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0161] In some embodiments, a cathode sheet can be manufactured in the following manner: a cathode slurry is formed by dispersing compositional components for manufacturing the cathode sheet described above, such as a cathode active material, a conductive agent, a binder, and any other compositional components, in a solvent (e.g., deionized water); the cathode slurry is applied to a cathode current collector, and a cathode sheet can be obtained through processes such as drying and cold pressing.

[0162] positive sheet

[0163] In some embodiments, the positive sheet comprises a positive current collector and a positive film layer provided on at least one surface of the positive current collector, the positive film layer comprises a positive active material, the positive active material comprises a first positive active material, and the first positive active material comprises a lithium-containing phosphate having an olivine structure. The lithium-containing phosphate having an olivine structure has a stable three-dimensional crystal lattice structure, and during the insertion and extraction of lithium ions, the structure can maintain relative stability, so that structural collapse and deformation do not easily occur, and as a result, the lithium-containing phosphate having an olivine structure is not damaged through multiple charge-discharge cycles, thereby extending the service life of the battery.

[0164] In this application, examples of lithium-containing phosphates having an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0165] As an example, the anode current collector has two opposing surfaces along its own thickness direction, and the anode film layer is provided on either one or both of the two opposing surfaces of the anode current collector.

[0166] In some embodiments, the lithium-containing phosphate of the olivine structure comprises a compound represented by formula (I): LiFe 1-x-y Mn x M 1 y PO4, Equation (I); in Equation (I), M 1is selected from at least one of V, Nb, Ti, Co, Ni, Sc, Ge, mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, A g, Sn, and Pb, and 0≤x≤1, 0≤y<1. The crystal lattice structure of the above-described lithium-containing phosphate is stable, and phase change does not occur easily, thereby further improving the safety performance of the secondary battery. For example, x is a value between a range consisting of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any two of these values. For example, y is a value between a range consisting of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any two of these values.

[0167] In some embodiments, the first positive active material further comprises a positive coating layer, the positive coating layer is provided on at least a portion of the surface of the lithium-containing phosphate, and the positive coating layer comprises at least one of a high-speed ion conductor material and a carbon material. The carbon material has a loose porous shape and allows the electrolyte and the lithium iron phosphate substrate to contact each other sufficiently effectively, thereby improving the infiltration performance of the electrolyte into the positive film layer and further improving the high-speed charging performance of the secondary battery. The high-speed ion conductor material has high ion conductivity, and it is advantageous to improve the high-speed charging performance of the battery by selecting and using a positive coating layer containing the high-speed ion conductor material.

[0168] In some embodiments, a positive electrode coating layer is provided on a lithium-containing phosphate surface, and the positive electrode film layer includes a high-speed ion conductor material and a carbon material.

[0169] In some embodiments, the positive electrode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a high-speed ion conductor material, and the second coating layer comprises a carbon material; the first coating layer is provided between a lithium-containing phosphate and the second coating layer. The carbon material generally has excellent adhesive performance, and in the above embodiments, providing the second coating layer containing the carbon material on the outer surface of the first positive electrode active material is advantageous for enhancing the adhesion between the first positive electrode active material and the current collector, thereby reducing the risk of the first positive electrode active material peeling off during battery use and improving the service life of the battery.

[0170] In some embodiments, the anode coating layer comprises a first coating layer and a second coating layer; the first coating layer comprises a high-speed ion conductor material, the second coating layer comprises a carbon material, and the second coating layer is provided between a lithium-containing phosphate and the first coating layer.

[0171] In the above embodiment, during the lithium ion transfer process, the lithium ions first pass through a first coating layer composed of a high-speed ion conductor material, then enter a second coating layer, and finally diffuse into the lithium-containing phosphate. This is advantageous for accelerating the movement speed of lithium ions within the first positive electrode active material and improving the high-speed charging performance of the battery. Additionally, the carbon material of the second coating layer has good electrical conductivity and can accelerate electron transport by forming a continuous electrical conductive network between the lithium-containing phosphate and the first coating layer, thereby further improving the high-speed charging performance of the battery.

[0172] In some embodiments, in the anode coating layer, the mass ratio of the high-speed ion conductor material to the carbon material is (0 to 100):(100 to 0). Controlling the mass ratio of the high-speed ion conductor material to the carbon material within the above-described range is advantageous for improving the high-speed charging performance of the battery. For example, the mass ratio of the high-speed ion conductor material to the carbon material is a value between the ranges consisting of 0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, or any two of these values.

[0173] In some embodiments, the high-speed ion conductor material comprises a compound represented by formula (II):

[0174] Li 3-b Fe 2-b M 2 b (PO4)3 formula (II);

[0175] In Equation (II), M 2 is selected from at least one of Ti, Zr, Hf, Ge, and Sn, and 0≤b≤1. The above-described high-speed ion conductor material has excellent ion conductivity, and selecting and using the above-described high-speed ion conductor material is advantageous for further improving the high-speed charging performance of the battery. For example, b is a value between the range of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any two of these values.

[0176] In some embodiments, the mass ratio of carbon elements in the first positive active material is 1% to 1.5%. By controlling the mass ratio of carbon elements in the first positive active material within the above-described range, on the one hand, the first positive active material is advantageous for realizing a high capacity and further, the secondary battery is advantageous for realizing a high energy density, on the other hand, the electron conductivity of the first positive active material is advantageous and further, the fast charging performance of the lithium-ion secondary battery is improved.

[0177] In this application, the mass ratio of carbon elements can be tested by methods known in the art. The anode sheet to be tested may be an anode sheet obtained by manufacturing, or an anode sheet obtained by disassembling a battery. Specifically, a battery is disassembled to obtain an anode sheet, the anode film layer is peeled off from the anode current collector to collect the anode film layer, then the anode film layer is dissolved in a suitable solvent, then the first anode active material is separated, and the mass ratio of carbon elements in the first anode active material is measured using a carbon-sulfur analyzer with reference to the standard GB / T20123-2006.

[0178] In some embodiments, the BET specific surface area of ​​the first positive active material is 12 m² 2 / g to 16m 2 / g is.

[0179] When the BET specific surface area of ​​the first cathode active material is within the range described above, the surface of the first cathode active material can provide more lithium ion insertion and extraction pathways. During the fast charging process, lithium ions can be inserted into the first cathode active material more quickly through these pathways, improving the fast charging performance of the battery by reducing the transport distance and resistance of the lithium ions. For example, the BET specific surface area of ​​the first cathode active material is 12 m² 2 / g, 12.2m 2 / g, 12.4m 2 / g, 12.6m 2 / g, 12.8m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 It is a value between / g or any two numeric values, but is not limited thereto.

[0180] In some embodiments, the tap density of the first positive active material is 0.8 g / cm³ 3 Up to 1.3 g / cm² 3The tap density of the first positive electrode active material is within the range described above, which is advantageous for forming a porous structure rich in the positive electrode film layer and ensures that the battery has superior high-speed charging performance. For example, the tap density of the first positive electrode active material is 0.8 g / cm³ 3 , 1.1g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.05g / cm 3 , 1.15g / cm 3 , 1.2g / cm 3 , 1.25g / cm 3 , 1.28g / cm 3 , 1.3g / cm 3 Or it is a value between a range consisting of any two numerical values, but is not limited thereto.

[0181] In some embodiments, the volume average particle size of the first positive active material is 1 μm to 3 μm. This is advantageous for forming a rich porous channel structure between the particles of the first positive active material, improving lithium ion and electron transport performance in the positive film layer, and further improving the mechanical performance of the secondary battery. For example, the volume average particle size Dv50 of the first positive active material is a value between a range consisting of 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3 μm, or any two numerical values, but is not limited thereto.

[0182] In some embodiments, the compaction density of the first positive active material under 50,000 N is 2.5 g / cm³ 3 Up to 2.6 g / cm² 3The compaction density of the first positive electrode active material is within the range described above, which is advantageous for making the contact between the first positive electrode materials tighter and improving the energy density of the battery. For example, the compaction density of the first positive electrode active material is 2.5 g / cm³ 3 , 2.51g / cm 3 , 2.52g / cm 3 , 2.53g / cm 3 , 2.54g / cm 3 , 2.55g / cm 3 , 2.56g / cm 3 , 2.57g / cm 3 , 2.58g / cm 3 , 2.59g / cm 3 , 2.60g / cm 3 Or it is a value between the range consisting of any two of these numbers.

[0183] 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. Since the lithium transition metal oxide has a higher specific capacity, selecting and using the lithium transition metal oxide as the second positive electrode active material is advantageous for further improving the energy density of the secondary battery.

[0184] In this application, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 It can also be abbreviated as), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM 523 It can also be abbreviated as), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM211 It can also be abbreviated as ), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 It can also be abbreviated as ), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 It can also be abbreviated as), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.1 Al 0.05 It may include at least one of O2) and its modified compounds, but is not limited thereto.

[0185] During the charging and discharging process, the battery involves the insertion / extraction and consumption of Li, and the molar content of Li changes when the battery is discharged in different states. In the example of the positive electrode active material in this application, the molar content of Li is the initial state of the material, i.e., the state before insertion, and when the positive electrode active material is applied to a battery system, the molar content of Li changes through charge-discharge cycles.

[0186] In the example of the positive electrode active material in this application, the molar content of oxygen is only a theoretical state value, and as the crystal lattice releases oxygen, the molar content of oxygen changes, and the actual molar content of oxygen may vary.

[0187] In some embodiments, the mass ratio of the first positive active material and the second positive active material is (99 to 90):(1 to 10). By controlling the mass ratio of the first positive active material and the second positive active material within the range described above, it is advantageous to consider both the service life and energy density of the secondary battery. For example, the mass ratio of the first positive active material and the second positive active material is a value between the ranges consisting of 99:1, 98:2, 97:3, 96:4, 95:5, 94:6, 93:7, 92:8, 91:9, 90:10, or any two of these values.

[0188] In some embodiments, the thickness of the positive film layer provided on a single side of the positive current collector is 100 μm to 200 μm; by controlling the thickness of the positive film layer within the above-described range, it is advantageous for the positive film layer to have high capacity, high lithium-ion and electron transport performance, and furthermore, it is advantageous for the secondary battery to have high energy density and fast charging performance. For example, the thickness of the positive film layer may be a value between a range consisting of 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, or any two of these values.

[0189] In some embodiments, the coating weight of the anode film layer provided on a single side of the anode current collector is 200 mg / 1540.25 mm 2 Up to 400 mg / 1540.25 mm 2 And; by controlling the coating weight of the anode film layer within the aforementioned range, the quantity of lithium ions released from the anode film layer per unit area can be improved, and furthermore, the energy density of the battery is improved. For example, the coating weight of the anode film layer is 200 mg / 1540.25 mm 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 , 390mg / 1540.25mm2 , 400mg / 1540.25mm 2 Or a value between a range consisting of any two numerical values. Optionally, the coating weight of the anode film layer is 250 / 1540.25 mm 2 Inner 320 / 1540.25mm 2 am.

[0190] In this application, the coating weight of the anode film layer can be tested using methods known in the art. The anode sheet to be tested may be an anode sheet obtained by manufacturing, or an anode sheet obtained by disassembling a battery. Specifically, an anode sheet is obtained by disassembling a battery, and the anode sheet has an area of ​​1540.25 mm² 2 Cut into a circular piece, weigh the mass m7 of the circular piece, then remove the anode film layer provided on one side of the circular piece, weigh the mass m8 of the circular piece, and calculate the coating weight of the anode film layer as m7-m8.

[0191] In some embodiments, the compaction density of the anode film layer is 2 g / cm³ 3 Up to 3g / cm² 3 The compaction density of the anode film layer is controlled within the aforementioned range, which is advantageous for the anode film layer to maintain an excellent pore structure, reduces the degree of bending of the anode film layer, and shortens the lithium ion transport path, thereby improving the high-speed charging performance and lifespan performance of the battery while simultaneously considering energy density. For example, the compaction density of the anode film layer is 2 g / cm³. 3 , 2.1g / cm 3 , 2.2g / cm 3 , 2.3g / cm 3 , 2.4g / cm 3 , 2.5g / cm 3 , 2.60g / cm 3 , 2.7 / cm 3 , 2.8g / cm 3 , 2.9g / cm 3 , 3g / cm 3Or it may be a value between the ranges consisting of any two of these values. Optionally, the compaction density of the anode film layer is 2.3 g / cm³ 3 Up to 2.5 g / cm² 3 am.

[0192] In some embodiments, the thickness of the positive current collector is 10 μm to 18 μm. Having the thickness of the positive current collector within the above-described range is advantageous for the battery to achieve high energy density on one hand, advantageous for reducing the risk of cracking of the positive current collector on the other, and further extends the service life of the battery. For example, the thickness of the positive current collector is a value between a range consisting of 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm, 17 μm, 17.5 μm, 18 μm, or any two of these values. Optionally, the thickness of the positive current collector is 13 μm to 15 μm.

[0193] In some embodiments, the positive current collector may use a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil may be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector is formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (e.g., a substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE), etc.).

[0194] In some embodiments, the anode film layer optionally further comprises a binder. As an example, the binder may comprise 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 acrylate resin.

[0195] In some embodiments, the anode film layer optionally further comprises a conductive agent. As an example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0196] In some embodiments, the anode film layer further comprises an anode dispersant, and the anode dispersant comprises at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, and carboxymethyl cellulose sodium. The anode dispersant described above has good flexibility and elasticity and can disperse the stress received by the anode active material during the compression process, and by selecting and using the anode dispersant described above, it is advantageous to achieve a high compaction density in the anode film layer and further improve the energy density of the battery.

[0197] In some embodiments, the mass ratio of the anode dispersant to the anode film layer is 0.3% to 5%. Optionally, it is 0.1% to 2%, more optionally 0.1% to 1%, and even more optionally 0.5% to 0.8%. Controlling the mass ratio of the anode dispersant in the anode film layer within the above-described range is advantageous for the battery to achieve high energy density. For example, the mass ratio of the anode dispersant may be a value between the ranges of 0.3%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, or any two of these values.

[0198] In some embodiments, an anode sheet can be manufactured in the following manner: compositional components for manufacturing the anode sheet described above, such as an anode active material, a conductive agent, a binder, and any other compositional components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form an anode slurry; the anode slurry is applied to a cathode current collector, and an anode sheet can be obtained through processes such as drying and cold pressing.

[0199] electrolytes

[0200] The electrolyte performs ion transfer between the anode sheet and the cathode sheet. The present application does not specifically limit the type of electrolyte and may select one as needed. For example, the electrolyte may be in a liquid state, a gel state, or a completely solid state.

[0201] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0202] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalate)borate, lithium bis(oxalate)borate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0203] In some embodiments, the solvent may 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0204] In some embodiments, the electrolyte further comprises an additive, and the additive comprises at least one of barium sulfate, polytrifluoroethyl methacrylate, bicyclic sulfate, tricyclic sulfate, tris(trimethylsilyl)phosphate, and vinylene carbonate. During the initial charge / discharge process of the battery, the above-described additive preferentially causes an electrochemical reduction reaction on the surface of the negative electrode sheet over solvent molecules in the electrolyte, thereby forming a dense and stable SEI film layer, which is advantageous for suppressing the growth of lithium dendrites and improving the safety performance of the battery.

[0205] In some embodiments, the mass ratio of the additive in the electrolyte is 1% to 10%. By controlling the mass ratio of the additive within the above-described range, it is advantageous to form an SEI film of appropriate thickness on the electrode surface, while on the one hand, it is advantageous to suppress the growth of lithium dendrites and improve the safety performance of the battery. On the other hand, it is advantageous to consider the transport resistance of lithium ions in the negative electrode sheet, thereby also considering the fast charging performance of the battery. For example, the mass ratio of the additive is a value between a range consisting of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any two of these values.

[0206] In some embodiments, the electrical conductivity of the electrolyte is 10 mS / cm to 18.5 mS / cm, and by selecting and using an electrolyte whose conductivity is within the range described above, the internal resistance of the battery can be reduced, energy consumption caused by resistance during the charging and discharging process is reduced, and the service life of the battery is extended. For example, the electrical conductivity of the electrolyte is a value between a range consisting of 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 any two of these values, and optionally, the electrical conductivity of the electrolyte is 14 mS / cm to 16.8 mS / cm.

[0207] In some embodiments, the electrolyte optionally further comprises additives. For example, it may include additives capable of improving specific performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery.

[0208] In some embodiments, the anode sheet, cathode sheet, and separator may be manufactured into an electrode assembly through a winding process or a lamination process.

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

[0210] In some embodiments, the outer packaging of the battery cell may be a rigid case, such as a rigid plastic case, an aluminum case, a steel case, etc. The outer packaging of the battery cell may also be a soft pack, such as an envelope-type soft pack. The material of the soft pack may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0211] The present application does not specifically limit the shape of the battery cell and may be cylindrical, square, or any other shape. For example, FIG. 1 is an exemplary square-shaped battery cell (5).

[0212] In some embodiments, with reference to FIG. 2, the outer packaging may include a case (51) and a cover plate (53). Here, the case (51) may include a bottom plate and a side plate connected to the bottom plate, and is surrounded by the bottom plate and the side plate to form a receiving cavity. The case (51) has an opening communicating with the receiving cavity, and the cover plate (53) may be installed as a cover over the opening to seal the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator may form an electrode assembly (52) through a winding process or a lamination process. The electrode assembly (52) is packaged within the receiving cavity. An electrolyte is infiltrated into the electrode assembly (52). The number of electrode assemblies (52) included in the battery cell (5) may be one or more, and a person skilled in the art may select according to specific needs.

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

[0214] FIG. 3 is an exemplary battery module (4). Referring to FIG. 3, in the battery module (4), a plurality of battery cells (5) may be arranged sequentially along the length direction of the battery module (4). Of course, they may also be arranged in any other arbitrary manner. Furthermore, the plurality of battery cells (5) may be secured through a fastening member.

[0215] Optionally, the battery module (4) may further include an external case having a receiving space, and a plurality of battery cells (5) are received in the receiving space.

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

[0217] FIGS. 4 and FIGS. 5 are an exemplary battery pack (1). Referring to FIGS. 4 and FIGS. 5, the battery pack (1) may include a battery box and a plurality of battery modules (4) installed within the battery box. The battery box includes an upper box (2) and a lower box (3), and the upper box (2) may be covered and installed on the lower box (3) to form a sealed space for accommodating the battery modules (4). The plurality of battery modules (4) may be arranged within the battery box in any manner.

[0218] electrical device

[0219] The present application further provides an electric device, wherein the electric device comprises a secondary battery provided in the first embodiment of the present application, and the secondary battery may comprise at least one of a battery cell, a battery module, or a battery pack. The secondary battery may be used as a power source for the electric device and may also be used as an energy storage unit for the electric device. The electric device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0220] As an electrical device, a battery cell, battery module, or battery pack can be selected depending on the usage needs.

[0221] FIG. 6 is an exemplary electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the electric device's need for high output and high energy density of a secondary battery, a battery pack or a battery module may be used.

[0222] Other examples of devices may include mobile phones, tablet PCs, laptops, etc. These devices generally require lightweight design and can use battery cells as a power source.

[0223] Examples

[0224] The following describes embodiments of the present application. The embodiments described below are illustrative and merely for the purpose of interpreting the present application and should not be understood as a limitation thereof. Specific techniques or conditions not specified in the embodiments shall be followed according to the techniques or conditions described in the literature of the art or according to product descriptions. Any reagents or equipment used without a specified manufacturer are ordinary products available for commercial purchase.

[0225] a. Preparation of the first graphite material and the second graphite material:

[0226] Preparation Example 1-1

[0227] Preparation of the first graphite material (Material 1-1):

[0228] Step 1: The needle coke raw material after oil-fired calcination is crushed and molded using an air jet mill to obtain a molded material with a Dv50 of 15 μm;

[0229] Step 2: The molding material described above is granulated together in a granulation reactor using granulation pitch (softening point 125°C; caulking value 51%) as a granulator to obtain a granulated material, wherein the mass ratio of the molding material to the granulator is 88:7.

[0230] Step 3: The above-described aggregated material was pre-carbonized at 1450°C for 5.2 hours under a nitrogen atmosphere to obtain an intermediate.

[0231] Step 4: The above-described intermediate was graphitized at a high temperature of 3000°C, and the graphitized particles were sieved and demagnetized to obtain a first graphite material.

[0232] Preparation Example 2-1

[0233] Preparation of the second graphite material (Material 2-1):

[0234] Step 1: The needle coke raw material after oil-fired calcination is crushed and molded using an air jet mill to obtain a molded material with a Dv50 of 22 μm;

[0235] Step 2: A molding material is granulated together in a granulation reactor using granulation pitch (softening point 113°C; caulking value 66%) as a granulator to obtain a granulated material, wherein the mass ratio of the molding material to the granulator is 90:6.

[0236] Step 3: The above-described aggregated material was pre-carbonized at 148°C for 4.7 hours under a nitrogen atmosphere to obtain an intermediate.

[0237] Step 4: The above-described intermediate was graphitized at a high temperature of 3000°C, and the graphitized particles were sieved and demagnetized to obtain a second graphite material.

[0238] B. Testing of the first graphite material and the second graphite material:

[0239] (1) I D / I G The test of:

[0240] Test the sample using a Raman spectrometer.

[0241] The test conditions are as follows: the excitation wavelength is 532 nm, the diffraction grating is 600 scales, the objective lens is 50x magnification, the integration time is 10 s, the accumulation count is 3, and surface scanning is performed to obtain the D peak and G peak intensities at 100 points, and the I of 100 points D / I GCalculate, and the I of each of the 30 maximum and minimum values D / I G Remove it, and the average value of the remaining 40 points is the material's I D / I G The test instrument can be the Horiba LabRAM HR800 Raman spectrometer.

[0242] Material 1-1's I D / I G is 0.51. Material 2-1's I D / I G is 0.13.

[0243] (2) Test of volume average particle size Dv50:

[0244] Tests are performed using a laser particle size analyzer in reference to GB / T 19077-2016. The test instrument may be a Mastersizer 3000 type laser particle size analyzer from Malvern Instruments Ltd., UK.

[0245] The Dv50 of material 1-1 is 11.8 μm. The Dv50 of material 2-1 is 18.3 μm.

[0246] (3) BET specific surface area test:

[0247] Refer to GB / T 19587-2017 and test using the nitrogen adsorption specific surface area analysis test method and calculate using the BET (Brunauer Emmett Teller) method. The specific surface area pore size analyzer Tri-Star 3020 from Micromeritics, USA may be used as the test instrument.

[0248] The BET specific surface area of ​​material 1-1 is 0.94 m² 2 It is / g. The BET specific surface area of ​​Material 2-1 is 1.78 m² 2 / g is.

[0249] (4) Test of tap density:

[0250] Referring to GB / T 5162-2006, the density can be measured using a powder tap density tester. The Dandong Baite BT-301 can be used as the test instrument, and the test parameters are as follows: vibration frequency 250±15 times / min, amplitude 3±0.2 mm, number of vibrations 5000 times, graduated cylinder 25 mL.

[0251] The tap density of Material 1-1 is 1.1 g / cm³ 3 The tap density of Material 2-1 is 1.05 g / cm³. 3 am.

[0252] Table 1

[0253]

[0254] C. Preparation of cathode slurry Preparation Example 3-1

[0255] A first cathode slurry was prepared by mixing a first graphite material (see Material 1-1 listed in Table 1), a first binder (styrene-butadiene rubber and lithium polyacrylate in a mass ratio of 2:1), a first dispersant (lithium carboxymethyl cellulose), and a first conductive agent (carbon nanotubes and conductive carbon black in a mass ratio of 5:5) in a mass ratio of 96.6:1.8:0.9:0.7.

[0256] Preparation Example 3-2

[0257] A second cathode slurry was prepared by mixing a second graphite material (see Material 2-1 listed in Table 1), a second binder (styrene-butadiene rubber and lithium polyacrylate with a mass ratio of 2:1.3), a second dispersant (lithium carboxymethyl cellulose), and a second conductive agent (carbon nanotubes and conductive carbon black with a mass ratio of 5:5) in a mass ratio of 97.8:1:0.7:0.5.

[0258] Preparation Example 3-3

[0259] A third cathode slurry was prepared by mixing a cathode active material (material 1-1 and material 2-1 with a mass ratio of 5:5), a second binder (styrene-butadiene rubber and lithium polyacrylate with a mass ratio of 2:1), a second dispersant (lithium carboxymethyl cellulose), and a second conductive agent (carbon nanotube and conductive carbon black with a mass ratio of 5:5) in a mass ratio of 96.9:1.8:0.8:0.5.

[0260] D. Manufacture of secondary batteries:

[0261] Example 1

[0262] 1. Manufacture of anode sheets:

[0263] A positive electrode active material (first positive electrode active material, lithium iron phosphate), conductive carbon black, polyvinylidene fluoride (PVDF), and a positive electrode dispersant (polyethylene glycol octylphenyl ether) were mixed in a mass ratio of 97.6:0.1:1.8:0.5, and then the solvent N-methylpyrrolidone was added and uniformly stirred to obtain a positive electrode slurry. The positive electrode slurry was applied to two surfaces of an aluminum foil positive electrode current collector, dried, and cold pressed to obtain a positive electrode sheet.

[0264] 2. Manufacture of the cathode sheet:

[0265] A first cathode slurry and a second cathode slurry were simultaneously extruded through a twin cavity slot die coater, wherein the mass ratio of the first cathode slurry to the second cathode slurry was 5:5. After drying and cold pressing, a cathode sheet was obtained. The second cathode slurry was applied to a cathode current collector (copper foil) to form a second film layer, and the first cathode slurry was applied to one side away from the cathode current collector to form a first film layer. Then, after drying, cold pressing, and slitting, a cathode sheet was obtained.

[0266] 3. Preparation of Electrolyte:

[0267] An organic solvent was formed by mixing a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) in a volume ratio of 3:7, a film-forming agent (barium sulfate, 2.5% mass ratio) was added, and LiPF6 was dissolved in the above-described organic solution to obtain an electrolyte with a LiPF6 concentration of 1 mol / L.

[0268] 4. Separator:

[0269] A polyethylene base film with a thickness of 5 μm is used, and a coating layer is applied to both sides of the base film, and the coating layer contains heat-resistant particles, and the heat-resistant particles include boehmite particles (inorganic particles) and an adhesive layer provided on the surface of the boehmite particles.

[0270] 5. Manufacture of secondary batteries:

[0271] The aforementioned positive electrode sheet, separator, and negative electrode sheet were stacked in sequence so that the separator would act as an isolation agent between the positive electrode sheet and the negative electrode sheet, and then an electrode assembly was formed through folding and winding. The electrode assembly was placed in an outer package and dried, and then the electrolyte prepared as described above was injected, and a secondary battery was obtained by undergoing processes such as vacuum packaging, settling, formation, and molding.

[0272] E. Testing of Separator Morphology:

[0273] The separator sheet is placed in a sample holder and locked in place, and a cross-sectional SEM image of the separator sheet is obtained using a scanning electron microscope (HR-TEM Talos F200). As shown in Fig. 7, and as can be seen from the cross-sectional SEM image, the coating layer contains heat-resistant particles, and the heat-resistant particles are interwoven to form a porous structure.

[0274] B. Test of compaction density:

[0275] (1) Test of compaction density of the anode film layer:

[0276] First, wipe off the anode film layer on one side of the anode sheet, cut it into a small circular piece with an area of ​​S21, weigh it, record it as M21, and the thickness H 21 The weight is measured. Then, the anode film layer of the anode sheet is wiped off and removed after weighing the aforementioned weight, the weight of the anode current collector is weighed and recorded as M20, and its thickness is recorded as H20. The weight of the single-sided coating of the anode sheet = (M21 - weight of the anode current collector M20) / S21, the thickness of the anode film layer = H21 - H20, and the compaction density of the anode film layer = weight of the single-sided coating of the anode film layer / thickness of the anode film layer.

[0277] (2) Test of compaction density of the cathode film layer:

[0278] First, wipe off the cathode film layer on one side of the cathode sheet, cut it into a small circular piece with an area of ​​S11, weigh it, and M 11 Recorded as, its thickness H11 The weight is measured. Then, the cathode film layer of the cathode sheet is wiped off and removed after weighing the aforementioned weight, the weight of the cathode current collector is weighed and recorded as M10, and its thickness is recorded as H10. The weight of the single-sided coating of the cathode sheet = (M11-M10) / S11, the thickness of the cathode film layer = H11-H10, and the compaction density of the cathode film layer = the weight of the single-sided coating of the cathode film layer / the thickness of the cathode film layer.

[0279] D. Performance testing of secondary batteries:

[0280] (1) Energy density test:

[0281] At 25℃, the battery cell is charged with a constant current of 0.33C to a cutoff voltage of 3.65V, and then charged with a constant voltage of 0.05C to 3.65V, at which point the secondary battery is in a fully charged state. After leaving the fully charged secondary battery standing for 5 minutes, it is discharged with a constant current of 0.33C to a cutoff voltage of 2.5V, and the discharge capacity at this time is the actual capacity of the secondary battery under 0.33C and is recorded as C0.

[0282] Then, the secondary battery was charged with a constant current of 0.33 C0 to a cutoff voltage of 3.65 V, and then discharged with a constant voltage of 0.05 C, at which point the secondary battery was in a completely discharged state. After leaving the completely discharged secondary battery standing for 5 minutes, it was discharged with a constant current of 0.33 C0 to a cutoff voltage of 2.5 V to obtain the discharge energy Q of the secondary battery.

[0283] The energy density of the secondary battery (Wh / Kg) = discharge energy Q of the secondary battery / mass M of the secondary battery, and the test results were recorded in Table 2 below.

[0284] (2) Safety performance test:

[0285] Take a secondary battery in a completely discharged state and place it in a heating box;

[0286] Gradually increasing the temperature of the heating box at a constant heating rate (3℃ / min);

[0287] Observe changes in the secondary battery, and stop heating the heating box when thermal runaway occurs in the secondary battery;

[0288] The maximum temperature at which thermal runaway occurred in the secondary battery was recorded.

[0289] Examples 2 to 3

[0290] Examples 2 and 3 manufacture secondary batteries in the same manner as Example 1, and the difference is

[0291] The cold pressing process of the anode sheet is controlled so that the compaction density of the anode film layer becomes as shown in Table 2.

[0292] In addition, the cold pressing process of the cathode sheet is controlled so that the compaction density of the cathode film layer is as shown in Table 2.

[0293] Examples 4 to 7

[0294] Examples 4 to 7 manufacture secondary batteries in the same manner as Example 1, the difference being that a base film of a corresponding thickness is used according to the description in Table 2.

[0295] Comparative Examples 1 and 2

[0296] Comparative Examples 1 and 2 manufacture secondary batteries in the same manner as Example 1, the difference being that a base film of a corresponding thickness is used according to the description in Table 2.

[0297] The performance of the secondary batteries prepared in Examples 2 to 7 and Comparative Examples 1 and 2 was tested in the same manner as in Example 1, and the test results were recorded in Table 2.

[0298] Table 2

[0299]

[0300] In the embodiments of the present application, the maximum temperature during thermal runaway indicates the safety performance of the secondary battery, and the higher the maximum temperature during thermal runaway, the lower the safety performance of the battery. If the maximum temperature during thermal runaway exceeds 300°C, it may cause thermal diffusion and seriously degrade the safety performance of the battery. Compared to Comparative Example 1 (base film thickness less than 4 μm), the secondary batteries manufactured in Examples 1 to 7 have improved safety performance.

[0301] As can be seen from the data of Comparative Example 2, when the base film thickness exceeds 12 μm, the effect of the base film thickness on improving the safety performance of the battery is limited, and at the same time, the energy density of the battery may decrease.

[0302] In Examples 1 to 7, the base film thickness of the manufactured secondary battery is between 4 μm and 12 μm, and the battery not only ensures high safety performance but also maintains high energy density.

[0303] Examples 8 to 11

[0304] Examples 8 to 11 manufactured secondary batteries in the same manner as Example 1, with the difference being that the parameters of the coating layer were adjusted according to the description in Table 3-1.

[0305] Example 12

[0306] Example 12 manufactures a secondary battery in the same way as Example 1, the difference being that the heat-resistant particles include boehmite particles and PVDF particles.

[0307] The performance of the secondary batteries prepared in Examples 8 to 12 was tested in the same manner as in Example 1, and the test results were recorded in Table 3-2.

[0308] Table 3-1

[0309]

[0310] Table 3-2

[0311]

[0312] As can be seen from the data in Tables 3-1 and 3-2, the thickness of the coating layer is set to 0.011 μm to 2 μm, the average particle size of the heat-resistant particles is 5 nm to 185 nm, and the particle areal density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 Up to 2.5 mg / 1540.25 cm 2 In this case, the manufactured secondary battery can be considered to have both high safety performance and high energy density.

[0313] As can be seen from the data in Tables 3-1 and 3-2, the thickness of the coating layer is set to 0.011 μm to 2 μm, the average particle size of the heat-resistant particles is 5 nm to 185 nm, and the particle areal density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 Up to 2.5 mg / 1540.25 cm 2 In this case, the manufactured secondary battery can be considered to have both high safety performance and high energy density.

[0314] Example 13

[0315] Example 13 manufactures a secondary battery in the same manner as Example 1, and the difference is

[0316] In the manufacturing process of the cathode sheet, the second cathode slurry was replaced with the third cathode slurry.

[0317] Examples 14 to 17

[0318] Examples 14 to 17 manufacture secondary batteries in the same manner as Example 13, and the difference is

[0319] In the process of manufacturing the cathode sheet, the mass ratio of the first graphite material and the second graphite material in the third cathode slurry is adjusted according to the description in Table 4, and / or the mass ratio of the first cathode slurry and the second cathode slurry (the thickness ratio of the first film layer and the second film layer in the corresponding cathode sheet) is adjusted.

[0320] Test of fast charging performance:

[0321] At 25℃, the secondary battery was charged with a constant current of 0.33C to a charge cutoff voltage of 3.65V, then charged with a constant voltage of 0.05C, and left to stand for 5 minutes. Afterward, the secondary battery was discharged with a constant current of 0.33C to a discharge cutoff voltage of 2.5V, and its actual capacity was recorded as C0.

[0322] Then, the secondary battery was charged with constant current sequentially to 1.0 C0, 1.3 C0, 1.5 C0, 1.8 C0, 2 C0, 2.3 C0, 2.5 C0, and 3.0 C0 to a charge cutoff voltage of 3.65 V or a negative cutoff potential of 0 mV (based on whichever was reached first), and after each charge was completed, it was discharged to 1 C0 to a discharge cutoff voltage of 2.5 V, and the corresponding negative potential was recorded when charging to 10% SOC, 20% SOC, 30% SOC, 40% SOC, 50% SOC, 60% SOC, 70% SOC, and 80% SOC (State of Charge) under different discharge ratios.

[0323] A charging ratio-cathode potential curve for different SOC states is fabricated, and after linear fitting, a charging ratio corresponding to when the cathode potential under different SOC states is 0 V is obtained, wherein the charging ratio is the charging range under the said SOC state, and each C 10% SOC , C 20% SOC , C 30% SOC , C 40% SOC , C 50% SOC , C 60% SOC , C 70% SOC , C 80% SOC It was recorded as.

[0324] According to the following formula:

[0325]

[0326] The charging time T (under the premise that lithium is not deposited in the secondary battery) for the above secondary battery to be charged from 10% SOC to 80% SOC was calculated, and the unit is min. The test results are recorded in Table 4.

[0327] The safety performance and energy density of the secondary batteries prepared in Examples 13 to 17 were tested in the same manner as in Example 1, and the test results were recorded in Table 4.

[0328] Table 4

[0329]

[0330] "Mass ratio" in Table 4 is the mass ratio of the second graphite material and the first graphite material.

[0331] As can be seen from the data in Table 4, when the second film layer includes the first graphite material and the second graphite material, the manufactured secondary battery combines safety performance and energy density, while the fast charging performance is further improved.

[0332] Examples 18 to 22

[0333] Examples 18 to 22 manufacture secondary batteries in the same manner as Example 13, and the difference is

[0334] A battery was manufactured using the first positive active material listed in Table 5-1. The parameters of each first positive active material are listed in Table 5-2.

[0335] The performance of the secondary batteries prepared in Examples 18 to 22 was tested in the same manner as in Example 1, and the test results were recorded in Table 5-2.

[0336] Table 5-1

[0337]

[0338] Table 5-2

[0339]

[0340] As can be seen from the data in Tables 5-1 to 5-2, when the anode coating layer includes a high-speed ion conductor material and / or a carbon material, the high-speed charging performance of the manufactured secondary battery is further improved.

[0341] Examples 23 to 25

[0342] Examples 23 to 25 are secondary batteries manufactured in the same manner as Example 13, with the difference being that at least one of the mixing ratio of each component in the positive active material, the coating weight of the positive slurry, and the thickness of the positive current collector is adjusted according to the description in Table 6-1.

[0343] The performance of the secondary batteries prepared in Examples 23 to 25 was tested in the same manner as in Example 1, and the test results were recorded in Table 6-2.

[0344] Table 6-1

[0345]

[0346] "Mass ratio" in Table 6-1 is the mass ratio of the first positive active material and the second positive active material.

[0347] Table 6-2

[0348]

[0349] As can be seen from the data in Tables 6-1 and 6-2, lithium transition metal oxide (NCM) in the anode film layer 811 When ) was added, the energy density of the obtained secondary battery was further improved.

[0350] Examples 26 and 27

[0351] Examples 26 and 27 manufacture secondary batteries in the same manner as Example 13, the difference being that the type or amount of the anode dispersant (mass ratio in the anode film layer) is controlled according to the description in Table 7, and the type or amount of the additive (mass ratio in the electrolyte) is controlled according to the description in Table 7.

[0352] The performance of the secondary batteries prepared in Examples 26 and 27 was tested in the same manner as in Example 1, and the test results were recorded in Table 7.

[0353] Table 7

[0354]

[0355] As can be seen from the data in Table 7, when the mass ratio of the anode dispersant in the anode sheet is 0.3% to 5% and the mass ratio of the additive in the electrolyte is 1% to 10%, the obtained secondary battery can be considered in terms of both energy density and safety performance.

[0356] It should be noted that the present application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiments that possess substantially the same technical concept, configuration, and functional effects within the scope of the technical solution of the present application fall within the technical scope of the present application. Furthermore, various modifications to the embodiments conceived by a person skilled in the art, and other forms constructed by combining some components of the embodiments, are also within the scope of the present application without departing from the spirit of the present application. Explanation of the symbols

[0357] 1: Battery pack 2: Upper box 3: Bottom box 4: Battery Module 5: Battery cell 51: Case 52: Electrode assembly 53: Cover plate

Claims

Claim 1 A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet comprises a positive current collector and a positive film layer provided on at least one surface of the positive current collector, and the compaction density of the positive film layer is 2.0 g / cm³ 3 Up to 3.0 g / cm² 3 The cathode sheet comprises a cathode current collector and a cathode film layer located on at least one surface of the cathode current collector, and the compaction density of the cathode film layer is 1.4 g / cm³ 3 Up to 1.85 g / cm² 3 A secondary battery comprising: a separator including a base film, wherein the thickness of the base film is 4 μm to 12 μm, the base film having nanopores, the average pore diameter of the nanopores being 10 nm to 300 nm, and the separator further including a coating layer provided on at least one side of the base film, wherein the coating layer includes heat-resistant particles, and the coating layer is installed between the base film and the anode sheet and between the base film and the cathode sheet; wherein the heat-resistant particles are interwoven to form a porous structure, the heat-resistant particles include inorganic particles, the mass ratio of the inorganic particles in the coating layer is 5% to 30%, and the average particle size of the heat-resistant particles is 5 nm to 185 nm. Claim 2 A secondary battery according to claim 1, wherein the thickness of the base film is 5 μm to 9 μm. Claim 3 A secondary battery according to claim 1, wherein the porosity of the base film is 20% to 70%. Claim 4 A secondary battery according to claim 1, wherein the thickness of the coating layer provided on one side of the base film is 0.011 μm to 3 μm. Claim 5 In claim 1, the particle areal density of the heat-resistant particles is 0.5 mg / 1540.25 cm 2 Up to 2.5 mg / 1540.25 cm 2 Phosphorus, secondary battery. Claim 6 A secondary battery according to claim 1, wherein, along the thickness direction of the base film, the heat-resistant particles include a first heat-resistant particle; and the heat-resistant particles include a first heat-resistant particle and a second heat-resistant particle; wherein the first heat-resistant particle is distributed on the surface of the base film and the second heat-resistant particle is laminated on one side away from the base film where the first heat-resistant particle is located. Claim 7 A secondary battery according to claim 1, wherein the heat-resistant particles also include adhesive particles, and / or the heat-resistant particles also include an adhesive layer provided on at least a portion of the surface of the inorganic particles. Claim 8 A secondary battery according to claim 1, wherein the inorganic particles comprise 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. Claim 9 In claim 1, the cathode film layer comprises a first film layer and a second film layer disposed between the first film layer and the cathode current collector, the first film layer comprises a first cathode active material, the first cathode active material comprises a first graphite material, and I of the first graphite material D / I G is 0.4 to 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 I of the second graphite material D / I G is 0.05 to 0.2 and; I D 1350±50cm in the Raman spectrum -1 Indicates the D peak intensity at the position, and I G 1580±50cm in the Raman spectrum -1 A secondary battery indicating the G-peak intensity at a position. Claim 10 In claim 9, 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, a secondary battery. Claim 11 A secondary battery according to claim 10, wherein the thickness of the negative electrode coating layer is 10 nm to 100 nm. Claim 12 A secondary battery according to claim 11, wherein the second film layer further comprises a first graphite material. Claim 13 A secondary battery according to claim 12, wherein the mass ratio of the second graphite material to the first graphite material in the second film layer is (3 to 5):(5 to 7). Claim 14 A secondary battery according to claim 9, wherein the ratio of the average thickness of the first film layer to the average thickness of the second film layer is (3 to 5):(5 to 7). Claim 15 In claim 1, the cathode film layer is provided on a single side of the cathode current collector, and the coating weight of the cathode film layer is 80 mg / 1540.25 mm 2 Up to 170 mg / 1540.25 mm 2 A secondary battery satisfying at least one of the following: the thickness of the cathode film layer provided on a single side of the cathode current collector is 40 μm to 75 μm. Claim 16 A secondary battery according to claim 1, wherein the thickness of the negative current collector is 4 μm to 8 μm. Claim 17 A secondary battery according to claim 1, wherein the positive film layer comprises a positive active material, the positive active material comprises a first positive active material, and the first positive active material comprises a lithium-containing phosphate having an olivine structure. Claim 18 In claim 17, the lithium-containing phosphate of the olivine structure comprises a compound represented by formula (I): LiFe 1-x-y Mn x M 1 y PO4, Equation (I); in the above Equation (I), M 1 A secondary battery selected from at least one of V, Nb, Ti, Co, Ni, Sc, Ge, mg, Al, Zr, Mn, Hf, Ta, Mo, W, Ru, A g, Sn and Pb, wherein 0≤x≤1 and 0≤y<1. Claim 19 In claim 17, the first positive active material further comprises a positive coating layer, said positive coating layer is provided on at least a portion of the surface of the lithium-containing phosphate, said positive coating layer comprises at least one of a high-speed ion conductor material and a carbon material, a secondary battery. Claim 20 A secondary battery according to claim 19, wherein in the anode coating layer, the mass ratio of the high-speed ion conductor material to the carbon material is (0 to 100):(100 to 0). Claim 21 A secondary battery according to claim 19, wherein the positive coating layer comprises a first coating layer and a second coating layer; wherein the first coating layer comprises a high-speed ion conductor material and the second coating layer comprises a carbon material; wherein the first coating layer is provided between the lithium-containing phosphate and the second coating layer; and wherein the second coating layer is provided between the lithium-containing phosphate and the first coating layer. Claim 22 In claim 19, the high-speed ion conductor material comprises a compound represented by formula (II): Li 3-b Fe 2-b M 2 b (PO4)3 Equation (II); in the above Equation (II), M 2 A secondary battery selected from at least one of Ti, Zr, Hf, Ge, and Sn, wherein 0≤b≤1. Claim 23 A secondary battery according to claim 19, wherein the mass ratio of carbon elements in the first positive electrode active material is 1% to 1.5%. Claim 24 In claim 17, the first positive active material has a BET specific surface area of ​​12 m² 2 / g to 16m 2 / g; the tap density of the first positive active material is 0.8g / cm³ 3 Up to 1.3 g / cm² 3 That the volume average particle size Dv50 of the first positive active material is 1 μm to 3 μm; and that the compaction density of the first positive active material under 50,000 N is 2.5 g / cm³ 3 Up to 2.6 g / cm² 3 A secondary battery that satisfies at least one of the following: Claim 25 A secondary battery according to claim 17, wherein the positive active material further comprises a second positive active material, and the second positive active material comprises a lithium transition metal oxide. Claim 26 A secondary battery according to claim 25, wherein the mass ratio of the first positive active material and the second positive active material is (99 to 90):(1 to 10). Claim 27 In claim 1, the anode film layer is provided on a single side of the anode current collector and has a thickness of 100 μm to 200 μm; the coating weight of the anode film layer is 200 mg / 1540.25 mm 2 Up to 400 mg / 1540.25 mm 2 A secondary battery that satisfies at least one of the following: Claim 28 A secondary battery according to claim 1, wherein the thickness of the positive current collector is 10 μm to 18 μm. Claim 29 A secondary battery according to claim 1, wherein the anode film layer further comprises an anode dispersant, and the anode dispersant comprises at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, and carboxymethyl cellulose sodium. Claim 30 A secondary battery according to claim 29, wherein the mass ratio of the anode dispersant to the anode film layer is 0.3% to 5%. Claim 31 In claim 1, 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, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone; and the electrolyte salt comprises lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium A secondary battery comprising at least one of bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalate)borate, lithium bis(oxalate)borate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate. Claim 32 A secondary battery according to claim 31, wherein the electrolyte further comprises an additive, and the additive comprises at least one of barium sulfate, polytrifluoroethyl methacrylate, bicyclic sulfate, tricyclic sulfate, tris(trimethylsilyl)phosphate, and vinylene carbonate. Claim 33 A secondary battery according to claim 32, wherein the mass ratio of the additive in the electrolyte is 1% to 10%. Claim 34 A secondary battery according to claim 33, wherein the electrical conductivity of the electrolyte is 10 mS / cm to 18.5 mS / cm. Claim 35 An electric device comprising a secondary battery according to any one of claims 1 to 34. Claim 36 delete Claim 37 delete Claim 38 delete

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