Secondary batteries and electrical devices

Abstract

The present application discloses a secondary battery and an electric device, the secondary battery comprising a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, where the non-faradaic charge of the negative electrode sheet is QC, which satisfies 0.05≦Q≦2.5, where Q=Cdl×ΔU, where Cdl nF is the non-faradaic capacity of the negative electrode sheet, and ΔUV is the potential range of the negative electrode active material layer. The negative electrode sheet of the present application is used in high energy density secondary battery products, which can better balance high charge / discharge characteristics and reduce interface degradation phenomena such as lithium precipitation caused by poor electrolyte infiltration, effectively reduce sheet polarization phenomena, improve battery consistency, prolong cycle life, and have excellent charge / discharge performance and dynamic performance.

Description

Technical Field

[0001] This application claims the priority of the Chinese patent application with the application number 202211175100.9, titled "Secondary Battery and Electrochemical Device", filed with the Chinese Patent Office on September 26, 2022, and all the contents of this application are incorporated herein by reference.

[0002] This application relates to the field of battery technology, and specifically to secondary batteries and electrochemical devices.

Background Art

[0003] With the rapid development of the new energy industry, there is an urgent need for secondary batteries with larger capacity, better durability, and stronger endurance performance. The negative electrode material is an important part of the secondary battery, and ensuring the high capacity of the negative electrode material while improving its cycle life is also one of the effective means to solve the above problems. Therefore, the problem of how to improve the cycle performance and cycle life of secondary batteries becomes a problem to be solved.

Summary of the Invention

Problems to be Solved by the Invention

[0004] This application provides a secondary battery and an electrochemical device, aiming to improve the cycle performance and cycle life of the battery.

Means for Solving the Problems

[0005] In a first aspect, this application provides a secondary battery, which includes a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. Here, the non-Faraday charge amount of the negative electrode sheet is QC, satisfying 0.05 ≤ Q ≤ 2.5, and Q = Cdl × ΔU, Cdl nF is the non-Faraday capacitance of the negative electrode sheet. ΔUV is the potential range of the negative electrode active material layer.

[0006] In some embodiments, Cdl satisfies 0.5 ≤ Cdl ≤ 5, and ΔU satisfies 0.1 ≤ ΔU ≤ 0.5.

[0007] In some embodiments, the negative electrode active material layer includes one or more of the following: artificial graphite, natural graphite, soft carbon, hard carbon, amorphous carbon, carbon fiber nanotubes, or mesocarbon microspheres.

[0008] In some embodiments, the contact angle of the negative electrode active material layer with respect to the surface of the electrolyte is θ, where θ satisfies 10° ≤ θ ≤ 40°.

[0009] In some embodiments, the resistance of the negative electrode active material layer is R mΩ, satisfying 5 ≤ R ≤ 20.

[0010] In some embodiments, the OI value of the negative electrode active material layer is between 2 and 15.

[0011] In some embodiments, the negative electrode active material layer contains a negative electrode active material, the quantity content of fine powder of the negative electrode active material is 0-80%, and the quantity content of coarse powder of the negative electrode active material is 0-60%.

[0012] The fine powder refers to negative electrode active material particles with a particle size of 2.2 μm or less, and the coarse powder refers to negative electrode active material particles with a particle size of 35 μm or more.

[0013] In some embodiments, the quantity content of the fine powder of the negative electrode active material is 0-40%.

[0014] The quantity content of the coarse powder in the negative electrode active material is 0-30%.

[0015] In some embodiments, the electrolyte includes a lithium salt additive, the lithium salt additive includes one or more of lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonimide), and lithium bis(fluorosulfonyl)imide.

[0016] In some embodiments, the content of the lithium salt additive in the electrolyte is X, satisfying the condition 0.1% ≤ X ≤ 2%.

[0017] In some embodiments, the negative electrode active material layer includes a protective film layer, the thickness of which is Hnm, and the condition 0.4 ≤ 10X·H + Q ≤ 36.

[0018] In some embodiments, the thickness H of the protective film layer satisfies 5 ≤ ​​H ≤ 180.

[0019] In the second aspect, the electrochemical apparatus relating to the present application includes the secondary battery described above. [Effects of the Invention]

[0020] Compared to conventional technology, the secondary battery of this invention limits the non-Faraday charge amount of the negative electrode sheet to a range of 0.05C to 2.5C, and satisfies Q=Cdl×ΔU by limiting the non-Faraday charge amount of the negative electrode sheet. As a result, in high-energy-density battery products, the negative electrode sheet can better balance high magnification and charge / discharge characteristics, avoid interfacial degradation phenomena such as lithium deposition due to poor electrolyte infiltration, effectively reduce the polarization phenomenon of the sheet, improve the consistency of the manufactured secondary batteries, extend the cycle life, and exhibit superior magnification performance and dynamic performance. [Brief explanation of the drawing]

[0021] [Figure 1] Figure 1 shows a fitting curve illustrating the scan speed-current scatter plot of the negative electrode sheet fabricated in Example 1. [Modes for carrying out the invention]

[0022] This application provides a secondary battery and an electrochemical device. In order to make the purpose, technical solution and effect of this application clearer and more definite, the following will further describe this application in detail with reference to the drawings and by giving examples. It should be understood that the specific examples described in this specification are only for the purpose of explaining this application and are not intended to limit this application.

[0023] With the development of the new energy industry, the demand for secondary batteries is increasing. For secondary batteries, such as lithium-ion batteries, when applied to electric vehicles, it is necessary to extend their single-trip range and service life as much as possible. Since the secondary batteries used in electric vehicles generate heat during the charge and discharge process, it accelerates the aging of the internal chemical system. Therefore, during the long-term cycle and storage process of secondary batteries, the attenuation of battery performance is caused, which is mainly manifested as the attenuation of the battery capacity, the increase of the internal resistance, and the decline of the power performance.

[0024] To improve the above problems, this application provides a negative electrode sheet with a specific non-Faradaic charge amount, so that the negative electrode sheet can better balance high rate and charge-discharge characteristics in high-energy-density battery products, reduce the occurrence of interface degradation phenomena such as lithium precipitation due to poor infiltration of the electrolyte, effectively reduce the polarization phenomenon of the sheet, improve the consistency of the manufactured secondary battery, increase the cycle life, and have excellent rate performance and kinetic performance.

[0025] In an embodiment of this application, this application provides a secondary battery, which includes the following positive electrode sheet, separator, electrolyte and negative electrode sheet.

[0026] I. Negative electrode sheet

[0027] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material.

[0028] 1. Non-Faradaic charge amount

[0029] One of the features of the secondary battery in this application is that the non-Faraday charge of the negative electrode sheet is QC, satisfying 0.05 ≤ Q ≤ 2.5, where Q = Cdl × ΔU. Cdl nF is the non-Faraday capacitance of the negative electrode sheet. ΔUV is the potential range of the negative electrode active material layer.

[0030] Here, the non-Faraday charge of the negative electrode sheet is QC, satisfying 0.05 ≤ Q ≤ 2.5. For example, the non-Faraday charge QC of the negative electrode sheet may be any of the following, or any two of them: 0.05C, 0.07C, 0.09C, 0.15C, 0.25C, 0.53C, 0.78C, 0.85C, 0.97C, 1.2C, 1.5C, 1.8C, 2.0C, 2.2C, 2.5C. Note that the specific numerical value of the non-Faraday charge Q is merely an example, and any value within the range of 0.05C to 2.5C is within the scope of protection of this application.

[0031] To make it easier to understand, the electrochemical reactions in secondary batteries are mainly surface reactions that occur on the electrode surface, and these reactions are as follows: (1) Mass transfer reaction, ions are transferred to the electrode surface. (2) Non-Faraday reaction, no charge transfer occurs through the electrode interface, and ions are physically adsorbed and desorbed on the surface of the active material to store and release charge. (3) Faraday reaction, the oxidation state of the active material changes, and charge moves into the interior of the active material. The non-Faraday capacity value (Cdl) can represent the number of active sites of the negative electrode active material on the negative electrode sheet, and its non-Faraday capacity value can be evaluated by the curve of the linear scanning voltammogram (LSV) at different scanning speeds that falls within the non-Faraday reaction range, i.e., by the change in current density with respect to the change in scanning speed. Specifically, the non-Faraday capacity value (Cdl) can affect the number of electrochemical active sites, affect the contact between the material and the electrolyte, affect the ion-electron conduction rate, lower the charge transfer resistance, and consequently affect the magnification performance.

[0032] This invention limits the non-Faraday charge amount of the negative electrode sheet to the above range, and by limiting the non-Faraday charge amount of the negative electrode sheet to satisfy Q = Cdl × ΔU, the negative electrode sheet can better balance high magnification and charge / discharge characteristics in high-energy-density secondary battery products, reduce interfacial degradation phenomena such as lithium deposition due to poor electrolyte infiltration, effectively reduce sheet polarization phenomena, improve the consistency of manufactured secondary batteries, extend cycle life, and exhibit excellent magnification and dynamic performance. The non-Faraday charge amount of the negative electrode can be adjusted by methods such as the form of the negative electrode active material, the compressed density of the negative electrode sheet, the OI value of the negative electrode sheet, the negative electrode configuration, and the negative electrode slurry process. The control of the non-Faraday charge amount of the negative electrode is not limited to the above methods, and it is sufficient if the negative electrode sheet can be controlled within the above range.

[0033] In the embodiments of this application, the non-Faraday capacitance Cdl nF of the negative electrode sheet satisfies 0.5 ≤ Cdl ≤ 5. For example, the non-Faraday capacitance (Cdl nF) of the negative electrode sheet may be within the range of 0.5 nF, 1 nF, 1.5 nF, 2 nF, 2.5 nF, 3 nF, 3.5 nF, 4 nF, 4.5 nF, 5 nF, or any two of these numbers. Note that the specific numerical values ​​of the non-Faraday capacitance Cdl nF are merely examples, and any value within the range of 0.5 nF to 5 nF is within the protected range of this application. By controlling the non-Faraday capacitance Cdl nF of the negative electrode sheet within the range of 0.5 nF to 5 nF, this application has made it possible to improve magnification performance by accelerating the ion-electron conduction rate, lowering the charge transfer resistance, and effectively improving the magnification performance.

[0034] In the embodiment of the present application, the non-Faraday capacitance Cdl nF of the negative electrode sheet satisfies 1.3 ≤ Cdl ≤ 4.7.

[0035] In the embodiment of the present application, the non-Faraday capacitance Cdl nF of the negative electrode sheet satisfies 1.4 ≤ Cdl ≤ 4.3. When the non-Faraday capacitance of the negative electrode sheet is within the above range, the number of active sites of the negative electrode active material in the negative electrode sheet is within a more appropriate range, resulting in a secondary battery with superior overall performance.

[0036] In the embodiments of this application, the potential range ΔUV of the negative electrode active material layer satisfies 0.1 ≤ ΔU ≤ 0.5. For example, the potential range ΔUV of the negative electrode active material layer may be any of 0.1V, 0.15V, 0.2V, 0.25V, 0.3V, 0.35V, 0.4V, 0.45V, 0.5V, or any two of these values. Note that the specific numerical values ​​of the potential interval ΔUV are merely examples, and any value within the range of 0.1V to 0.5V is within the protected range of this application. By controlling the potential range ΔUV of the negative electrode active material layer to the range of 0.1V to 0.5V, this application is advantageous for contact between the material and the electrolyte, accelerates the ion-electron conduction rate, lowers the charge transfer resistance, and effectively improves efficiency performance.

[0037] 2, negative electrode active material layer

[0038] The negative electrode active material layer may be a single layer or a multilayer, and each of the multilayer negative electrode active material layers may contain the same or different negative electrode active material. In the embodiments of the present application, in order to prevent lithium metal from being deposited on the negative electrode sheet during charging, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material.

[0039] In the embodiments of this application, the negative electrode active material layer includes, but is not limited to, artificial graphite, natural graphite, soft carbon, hard carbon, amorphous carbon, carbon fiber nanotubes, and mesocarbon microspheres. The negative electrode active material may be used alone or in any combination.

[0040] In the embodiments of this application, the negative electrode active material layer includes, but is not limited to, petroleum coke and acicular coke having a relatively small microcrystalline structure, a relatively large amount of damascene structure, and a relatively small amount of streamlined structure. The negative electrode active material may be used alone or in any combination. By employing materials with the above structural characteristics, the negative electrode active material layer provides the negative electrode sheet with excellent isotropy and good magnification performance, ensuring relatively low resistance and material stability during the cycle process.

[0041] The microcrystalline structure, damascene structure, and streamlined structure of the aforementioned negative electrode active material can be determined by observing them using a scanning electron microscope (SEM).

[0042] In the embodiments of this application, the surface of the negative electrode active material may have a coating layer, which may be a single layer or two layers. For example, the surface of the negative electrode active material may be coated with soft carbon, which can accelerate electron conduction, thereby improving the conductivity of the material while protecting the graphite itself. By coating the surface of the negative electrode active material with an inorganic material, the formation of a thin and dense solid electrolyte interface (SEI) film layer can be promoted, providing a stable chemical and electrochemical reaction interface and improving the long cycle performance of the material.

[0043] To make it clear, by employing a two-layer coating, this invention can effectively suppress side reactions in secondary batteries while maintaining the integrity of the graphite. By adjusting the coating agents and coating processes of the inner and outer layers, the electronic and ionic conductivity of the material can be effectively controlled, thereby effectively controlling the rate of the non-Faraday process of the electrodes and ultimately controlling the performance of the battery.

[0044] The coating layer of the negative electrode active material layer can be observed using a transmission electron microscope (TEM).

[0045] In the embodiments of this application, the contact angle θ of the negative electrode active material layer with respect to the surface of the electrolyte is denoted as θ, where θ satisfies 10° ≤ θ ≤ 40°. For example, the contact angle θ of the negative electrode active material layer with respect to the surface of the electrolyte may be within the range of 10°, 15°, 20°, 25°, 30°, 35°, 40°, or any two of these numbers.

[0046] The contact angle of the negative electrode active material layer with respect to the electrolyte surface can reflect the surface properties of the negative electrode active material layer. When the wetting contact angle between the negative electrode sheet and the electrolyte is small, the electrolyte is adsorbed immediately after being dropped onto the negative electrode sheet. This indicates better compatibility between the negative electrode sheet and the electrolyte, and therefore the electrolyte comes into close contact with the surface active sites of the negative electrode sheet. Furthermore, the diffusion transfer efficiency of lithium ions from the electrolyte to the graphite surface is improved, which is an advantage in terms of superior dynamic performance.

[0047] This invention controls the contact angle of the negative electrode active material layer with respect to the electrolyte surface within the above range. When the contact angle of the negative electrode active material layer with respect to the electrolyte surface is within the above range, defects such as pinholes and pits in the negative electrode sheet are reduced. The greater the tendency of the electrolyte to spread onto the negative electrode sheet, the greater the wettability and the better the compatibility with the electrolyte. As a result, lithium ions are more easily transferred to the negative electrode sheet, which is advantageous in reducing the internal resistance of the battery. This reduces defects such as lithium deposition due to poor penetration, increased by-products, and poor dynamic performance, improving the magnification performance and cycle life. On the other hand, by shortening the standing time after filling the secondary battery with electrolyte and improving the penetration rate of the electrolyte into the negative electrode sheet, production efficiency and yield rate are improved. The state of the sheet interface of the manufactured batteries becomes more uniform, the current density at the interface during the charge and discharge process becomes more uniform, and the dynamic performance and cycle life of the battery are improved.

[0048] In the embodiments of this application, the contact angle of the negative electrode active material layer with respect to the surface of the electrolyte is θ, where θ satisfies 12° ≤ θ ≤ 35°. When the contact angle of the negative electrode active material layer with respect to the surface of the electrolyte is within the above range, surface defects on the negative electrode sheet are further reduced, the battery has higher production efficiency and yield rate, and the overall performance of the battery is further improved.

[0049] In the embodiments of this application, the contact angle θ of the negative electrode active material layer with respect to the surface of the electrolyte can be measured using an optical contact angle meter by the GB / T 30447-2013 nanofilm contact angle measurement method.

[0050] Here, the electrolyte contains lithium hexafluoride phosphate, which is a lithium salt, cyclic carbonate esters and chain carbonate esters, which are organic solvents, and an electrolyte additive.

[0051] In the embodiments of the present application, the resistance of the negative electrode active material layer is R mΩ, satisfying 5 ≤ R ≤ 20. For example, the resistance R mΩ of the negative electrode active material layer may be within the range of 5 mΩ, 7.5 mΩ, 10 mΩ, 12.5 mΩ, 15 mΩ, 17.5 mΩ, 20 mΩ, or any two of these numbers.

[0052] To understand this, factors influencing the resistance of the negative electrode sheet of a secondary battery include the interface between the current collector and the active material layer, the distribution of the conductive agent, and the contact state between particles. The resistance of the active material layer of the negative electrode sheet can reflect the state and performance of the material in the negative electrode sheet. Relatively low resistance of the active material layer can be obtained by adjusting parameters such as the interface between the negative electrode current collector and the negative electrode active material layer, the distribution of the conductive agent, and the contact state between particles. A negative electrode sheet with a resistance value within the above range has relatively high electron transfer efficiency, and the relatively low resistance between the current collector and the electrode active material layer can effectively reduce the DC internal resistance of the battery, improve the battery's power performance, and make it less likely for the battery to experience phenomena such as large polarization and lithium deposition during long-term cycle processes, thereby effectively improving the battery's cycle performance. On the other hand, the reduced resistance of the negative electrode active material layer shortens the lithium ion transfer path.

[0053] In the embodiments of this application, the resistance of the negative electrode active material layer is R mΩ, satisfying 5 ≤ R ≤ 18. When R mΩ is within the above range, the battery has better power performance and cycle performance.

[0054] In the embodiment of the present invention, the resistance of the negative electrode active material layer is R mΩ, satisfying 5 ≤ R ≤ 12. When R mΩ is within the above range, the interface between the negative electrode current collector and the negative electrode active material layer, the distribution of the conductive agent, and the contact state between particles are improved, and the battery has better overall performance.

[0055] In the embodiments of this application, the method for testing the resistance R mΩ of the negative electrode active material layer is as follows.

[0056] A negative electrode sheet with negative electrode active material layers on both sides has an area of ​​1540.25 mm². 2 The negative electrode sheet is cut into a circular sheet, and the cut negative electrode sheet is placed in the center of the probe of a sheet resistance meter. Then, the negative electrode sheet is tested using the sheet resistance meter, and the resistance of the negative electrode active material layer of the measured negative electrode sheet is obtained. After measuring each of the 10 selected negative electrode sheet samples with the sheet resistance meter, the average resistance of the negative electrode active material layer of the 10 measured negative electrode sheets is calculated to obtain the resistance of the negative electrode active material layer.

[0057] In the embodiments of this application, the magnitude of the OI value of the negative electrode active material layer is 2 to 15. For example, the OI value of the negative electrode active material layer may be any of 2, 4, 6, 8, 10, 12, or 15, or any two of these numbers. Note that the specific numerical values ​​of the OI value are merely examples, and any value within the range of 2 to 15 is within the scope of protection of this application.

[0058] Here, the OI value of the negative electrode active material layer refers to the ratio of the intensities of the X-ray diffraction peaks of the negative electrode active material layer in the 004 crystal plane and the 110 crystal plane.

[0059] To understand this, the OI value (C004 / C110) of the negative electrode sheet can affect the lithium ion transfer path. During the lithium storage process, lithium ions enter the interlayer from the edge face of the graphite negative electrode material, undergo solid-phase diffusion between the layers, and complete the lithium storage process, exposing the relatively small graphite edge face with an isotropic microcrystalline structure to the sheet surface.

[0060] Therefore, when the compressive density of the negative electrode sheet matches the coating surface density, if the OI value of the negative electrode sheet is within the above range, it can influence the lithium ion transition path, lithium ion transition rate, and electrochemical reaction dynamics, thereby further realizing high multiplier discharge performance of lithium ions and ensuring relatively low impedance during the cycle process. In addition, when the OI value of the negative electrode sheet is within the above range, expansion between graphite layers is suppressed, ensuring relatively high stability of the material structure during the cycle process, improving cycle performance, and ultimately achieving the objective of improving multiplier charging capability and optimizing the cycle.

[0061] In the embodiments of the present invention, adjusting the OI value of the negative electrode active material is more advantageous for controlling the sheet OI value. The OI value of the negative electrode active material can be changed by adjusting the physicochemical properties of the negative electrode active material, such as particle size and powder resistance. The OI value of the negative electrode sheet can be changed by adjusting elements such as the proportion of conductive agent, stirring process, and rolling process.

[0062] In this invention, by controlling the OI value of the negative electrode active material layer within the above range, the transition path of lithium ions is shortened, high-speed transition of lithium ions is achieved, electrochemical reaction dynamics are accelerated, and consequently, high multiplier discharge performance of lithium ions is further realized, and low impedance is ensured during the cycle process. On the other hand, expansion between graphite layers is suppressed, relatively high stability of the material structure is ensured during the cycle process, improving cycle performance, and consequently improving multiplier charging capability, thus achieving the objective of optimizing the cycle.

[0063] In the embodiments of this application, the OI value of the negative electrode active material layer is between 2 and 10. When the OI value of the negative electrode active material layer is within the above range, the battery has better overall performance.

[0064] In the embodiments of the present application, the negative electrode active material layer includes, but is not limited to, artificial graphite, natural graphite, soft carbon, amorphous carbon, carbon fiber nanotubes, and mesocarbon microspheres. The negative electrode active material may be used alone or in any combination.

[0065] In the embodiments of this application, the negative electrode active material layer includes, but is not limited to, petroleum coke and acicular coke having a relatively small microcrystalline structure, a relatively large amount of damascene structure, and a relatively small amount of streamlined structure. The negative electrode active material may be used alone or in any combination.

[0066] The quantity content of the fine powder of the negative electrode active material is 0 to 80%. For example, the quantity content of the fine powder of the negative electrode active material may be any of the following: 0, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any two of these numbers. The specific numerical values ​​for the quantity content of the fine powder are merely examples, and any value within the range of 0 to 80% is within the scope of protection of this application.

[0067] The quantity content of the coarse powder of the negative electrode active material is 0 to 80%. For example, the quantity content of the coarse powder of the negative electrode active material may be any of 0, 10%, 20%, 30%, 40%, 50%, 60%, or any two of these numbers. The specific numerical values ​​for the quantity content of the coarse powder are merely examples, and any value within the range of 0 to 60% is within the scope of protection of this application.

[0068] Here, the fine powder refers to negative electrode active material particles with a particle size of 2.2 μm or less, and the coarse powder refers to negative electrode active material particles with a particle size of 35 μm or more.

[0069] In the embodiments of the present application, the quantity content of the fine powder of the negative electrode active material is 0 to 40%, and for example, the quantity content of the fine powder of the negative electrode active material may be in the range of 0, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any two of these numbers.

[0070] The quantity content of the coarse powder of the negative electrode active material is 0 to 30%. For example, the quantity content of the coarse powder of the negative electrode active material may be within the range of 0, 10%, 15%, 20%, 25%, 30%, or any two of these numbers.

[0071] To make it easier to understand, a small quantity of fine powder in the negative electrode active material results in fewer negative electrode active material particles with a particle size of 2.2 μm or less, and a small quantity of coarse powder in the negative electrode active material results in fewer negative electrode active material particles with a particle size of 35 μm or more. Limiting both together prevents voids caused by an excess of large negative electrode active material particles from being filled with an excess of small negative electrode active material particles, thereby widening the gaps between negative electrode active material particles, which is advantageous for the Faraday reaction in the battery, increases the non-Faraday capacity Cdl of the negative electrode sheet, increases the number of electrochemically active sites, is advantageous for contact between the material and the electrolyte, accelerates the ion-electron conduction rate, lowers the charge transfer resistance, and effectively improves the multiplier performance of the secondary battery.

[0072] To make it easier to understand, in this application, the quantity content of fine powder in the negative electrode active material is controlled to be within the range of 0 to 40%, and the quantity content of coarse powder in the negative electrode active material is controlled to be within the range of 0 to 30%, and by limiting both together, the width of the particle size distribution of the negative electrode active material can be effectively restricted, the particle size distribution of the negative electrode active material becomes more concentrated, the morphology becomes more regular, excellent isotropy of the negative electrode active material is ensured, the electronic conductivity and ion transfer of the negative electrode active material are improved, and consequently the rate of the non-Faraday process of the sheet can be effectively adjusted and controlled.

[0073] In the embodiment of the present invention, a particle size distribution test of the negative electrode active material can be performed using a laser particle size analyzer to determine the quantity content of fine powder and coarse powder of the negative electrode active material. By calculating the peak areas corresponding to the fine powder and coarse powder, specific numerical values ​​for the quantity content of fine powder and coarse powder of the negative electrode active material can be obtained.

[0074] In the embodiments of this application, the negative electrode active material layer 120 includes a protective film layer 130, the thickness of the protective film layer 130 is Hnm, and the condition 5 ≤ H ≤ 180 is satisfied. For example, the thickness Hnm of the protective film layer 130 may be any of 5nm, 30nm, 60nm, 90nm, 120nm, 150nm, 160nm, or any two of these numbers. Note that the specific numerical value of the thickness Hnm is merely an example, and any value within the range of 5nm to 180nm falls within the protection range of this application. When the thickness of the protective film layer is within this range, the negative electrode active material can be protected more effectively while reducing the effects caused by the protective film layer, such as an increase in internal resistance.

[0075] The thickness of the protective film layer can be determined by employing a TEM test.

[0076] 3, negative electrode current collector

[0077] In the embodiments of this application, the negative electrode current collector includes, but is not limited to, metal foil, metal cylinder, metal tape roll, metal plate, metal film, metal plate mesh, stamping metal, foamed metal, etc. In some embodiments, the negative electrode current collector is metal foil. In some embodiments, the negative electrode current collector is copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0078] 4. Testing and calculation of the non-Faraday charge of the negative electrode sheet.

[0079] In embodiments of the present application, the present application further provides a method for testing and calculating the non-Faraday charge of any of the above-described negative electrode sheets, which specifically includes the following steps:

[0080] S1. Assemble the negative electrode sheet into a button cell, perform a cyclic voltamomorphism (CV) test on the button cell, and obtain the UV potential range of the button cell.

[0081] In step S2, the potential range U of the button cell in step S1 is selected, and a linear scanning voltammogram (LSV) test is performed on the button cell to detect the scanning speed-voltage graph and voltage-current graph. Based on the voltage-current graph, the potential range ΔUV of the negative electrode active material layer is obtained, where the scanning direction is from low potential to high potential.

[0082] In step S3, based on step S2, a scan rate-current scatter plot is detected, and based on the scan rate-current scatter plot, the non-Faraday capacitance value Cdl of the negative electrode sheet is obtained.

[0083] In step S4, based on the potential range ΔU and the non-Fraday capacitance value Cdl obtained in steps S2 and S3, the non-Fraday charge Q is calculated using the formula Q = Cdl × ΔU.

[0084] In the embodiments of this application, the step of assembling the negative electrode sheet into a button cell in step S1 specifically includes disassembling the secondary battery in a glove box or drying chamber to obtain a negative electrode overhang region sheet, immersing it in a dimethyl carbonate (DMC) solution, cutting it, and then assembling it with a metallic lithium sheet into a button cell. A negative electrode sheet that has not been assembled into a battery may also be used.

[0085] Here, the overhang region refers to the portion of the negative electrode sheet that extends beyond the positive electrode sheet in both length and width directions.

[0086] The button battery in step S1 includes a positive electrode housing, a negative electrode sheet, a separator, an electrolyte, a lithium sheet, foamed nickel, a gasket, and the negative electrode housing.

[0087] In the embodiments of this application, the potential range UV of the button cell in step S1 satisfies 2.5 ≤ U ≤ 3. For example, the potential range UV of the button cell may be any of 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, 3V, or any two of these numbers. Note that the specific numerical values ​​of the potential range UV are merely examples, and any value within the range of 2.5V to 3V is within the protected range of this application.

[0088] In the embodiments of this application, the scanning speed in the cyclic Voltamo method in step S1 is V1, satisfying 0.1mV / s ≤ V1 ≤ 1mV / s. For example, the scanning speed V1 may be any of 0.1mV / s, 0.2mV / s, 0.3mV / s, 0.4mV / s, 0.5mV / s, 0.6mV / s, 0.7mV / s, 0.8mV / s, 0.9mV / s, 1mV / s, or any two of these numbers. The specific numerical values ​​of the scanning speed V1 are merely examples, and any value within the range of 0.1mV / s to 1mV / s is within the scope of protection of this application.

[0089] To make it clear, the cyclic Voltamo method (CV) in the test and calculation method for the non-Faraday charge of a negative electrode sheet provided in this application has advantages such as being easy to manufacture, easy to operate, providing accurate and stable test data, and being safe and environmentally friendly, thus having practical application value.

[0090] In the embodiments of this application, the potential range ΔUV of the negative electrode active material layer in step S2 satisfies 0.1 ≤ ΔU ≤ 0.5. For example, the potential range ΔUV of the negative electrode active material layer may be any of 0.1V, 0.15V, 0.2V, 0.25V, 0.3V, 0.35V, 0.4V, 0.45V, 0.5V, or any two of these numbers. Note that the specific numerical values ​​of this potential interval ΔUV are merely examples, and any value within the range of 0.1V to 0.5V is within the protected range of this application.

[0091] In the embodiments of this application, in step S2, the scanning speed V2 in the linear scanning voltammogram method satisfies 0.05mV / s ≤ V2 ≤ 5mV / s. For example, the scanning speed V2 may be any of 0.05mV / s, 0.5mV / s, 1mV / s, 1.5mV / s, 2mV / s, 2.5mV / s, 3mV / s, 3.5mV / s, 4mV / s, 4.5mV / s, 5mV / s, or any two of these numbers. The specific numerical value of the scanning speed V2 is merely an example, and any value within the range of 0.05mV / s to 5mV / s is within the scope of protection of this application.

[0092] In the embodiments of the present invention, step S3 includes detecting a scan rate-current scatter plot based on step S2 and obtaining a non-Faraday capacitance value Cdl of the negative electrode sheet based on the scan rate-current scatter plot, as follows:

[0093] When performing a linear scanning voltammogram test on a button battery, multiple scanning speeds are selected, and multiple voltage medians are obtained based on the scanning speed-voltage graph detected in step S2, where each scanning speed corresponds to a corresponding voltage median.

[0094] Multiple current values ​​are obtained based on the acquired voltage medians and voltage-current graphs, where each current value corresponds to the corresponding voltage median.

[0095] By determining the correspondence between each scanning speed and the median voltage, and the correspondence between each current value and the median voltage, a mapping relationship between scanning speed and current value was established, and a scanning speed-current scatter plot was detected.

[0096] A linear function is obtained by fitting based on the scan rate-current scatter plot. Here, the slope of the linear function is the non-Faraday capacitance value Cdl of the negative electrode sheet.

[0097] 5. Manufacturing of negative electrode sheets

[0098] The negative electrode sheet in the secondary battery of the present invention can be manufactured using any known method. For example, a slurry can be prepared by adding a conductive agent, a binder, an additive, and a solvent to the negative electrode active material, coating the negative electrode current collector with the slurry, drying it, and then forming the electrode by rolling.

[0099] II, electrolyte

[0100] The electrolyte used in the secondary battery of this invention comprises an electrolyte and a solvent that dissolves the electrolyte.

[0101] 1. Additives

[0102] In the embodiments of this application, the electrolyte includes, but is not limited to, lithium tetrafluoroborate (abbreviated as LiBF4), lithium bis(oxalato)borate (abbreviated as LiBOB), lithium difluorophosphate (abbreviated as LiPO2F2), lithium bis(trifluoromethanesulfonimide) (abbreviated as LiTFSI), and lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI). The above lithium salt additives may be used individually or in any combination.

[0103] In the embodiments of this application, the content of the lithium salt additive in the electrolyte is X, based on the mass of the electrolyte, and satisfies 0.1% ≤ X ≤ 2%. For example, the content X of the lithium salt additive in the electrolyte may be any of 0.1%, 0.4%, 0.7%, 1%, 1.3%, 1.6%, 2%, or any two of these numbers. Note that the specific numerical value of the content X is merely an example, and any value within the range of 0.1% to 2% is within the scope of protection of this application.

[0104] In the embodiments of this application, the content X of the lithium salt additive in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 0.4 ≤ 10X·H + Q ≤ 36. When the above range is satisfied, the battery has better overall performance.

[0105] 2, electrolyte

[0106] In this application, the electrolyte is not particularly limited and can be any known substance that can be used as an electrolyte, as long as it does not impair the effects of this application. In the case of secondary batteries, lithium salts are usually used. In the embodiments of this application, the electrolyte contains LiPF6, but is not limited thereto.

[0107] On the other hand, in this application, the electrolyte content is not particularly limited as long as it does not impair the effects of this application. For example, the electrolyte content may be 0.8 mol / L to 2.2 mol / L.

[0108] 3. Solvents

[0109] In this application, the solvent may be any known substance that can be used as a solvent, as long as it does not impair the effects of this application, and is not particularly limited.

[0110] In the embodiments of this application, the solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), butylene carbonate (BC), and methyl vinyl carbonate (MEC). The above solvents may be used individually or in any combination.

[0111] III, positive electrode sheet

[0112] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector.

[0113] 1.Cathode active material layer

[0114] The positive electrode active material layer may be a single layer or a multilayer, and each of the multilayer negative electrode active material layers may contain the same or different positive electrode active material. The positive electrode active material is any material capable of reversibly intercepting and releasing metal ions such as lithium ions.

[0115] positive electrode active material

[0116] The positive electrode active material layer includes, but is not limited to, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate (LFP), and a ternary material.

[0117] In the embodiments of this application, the ternary material includes, but is not limited to, lithium nickel-cobalt manganese oxide and lithium nickel-cobalt aluminate.

[0118] In the embodiments of the present application, the positive electrode active material contains lithium nickel-cobalt-manganate, and in the lithium nickel-cobalt-manganate, if the moles of nickel, cobalt, and manganese are considered to be 1, the nickel content is 0.5 or more.

[0119] In the embodiments of the present application, the positive electrode active material contains lithium nickel-cobalt-manganate, and in the lithium nickel-cobalt-manganate, if the molar ratio of nickel, cobalt, and manganese is 1, the nickel content is 0.85 or less.

[0120] In the embodiments of the present application, the positive electrode active material includes at least one of NCM523, NCM622, or NCM811.

[0121] In the embodiments of the present application, the positive electrode active material further contains doping elements, and the doping elements may include elements such as aluminum, magnesium, titanium, and zirconium, if they can further stabilize the structure of the positive electrode active material.

[0122] In the embodiments of the present application, the positive electrode active material may further contain coating elements that include elements such as aluminum, magnesium, titanium, and zirconium, if this can further stabilize the structure of the positive electrode active material.

[0123] Positive electrode conductive agent

[0124] In this application, the type of positive electrode conductive agent is not particularly limited and any known substance that can be used as a conductive material is used, as long as it does not impair the effects of this application.

[0125] In the embodiments of this application, the positive electrode conductive agent includes, but is not limited to, graphite such as natural graphite or artificial graphite, carbon black such as acetylene black, amorphous carbon materials such as needle-shaped coke, carbon nanotubes, graphene, etc. The above positive electrode conductive agents may be used individually or in any combination.

[0126] Positive electrode binder

[0127] The type of positive electrode binder is not particularly limited as long as it does not impair the effects of the present invention. Specifically, in the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used during the manufacture of the electrode is acceptable.

[0128] In the embodiments of this application, the positive electrode binder can be a positive electrode conductive material such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, or nitrocellulose, either alone or in combination.

[0129] 2, positive electrode current collector

[0130] In this application, the type of positive electrode current collector is not particularly limited and any known material that can be used as a positive electrode current collector can be used, as long as it does not impair the effects of this application.

[0131] In the embodiments of this application, the positive electrode current collector includes, but is not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metal material. In one embodiment, the positive electrode current collector is aluminum foil.

[0132] 3. Manufacturing of positive electrode sheets

[0133] The positive electrode sheet in the secondary battery of this invention can be manufactured using any known method. For example, a slurry may be prepared by adding a conductive agent, a binder, and a solvent to the positive electrode active material, coating the slurry with the positive electrode current collector, drying, and then rolling to form the electrode. Alternatively, a sheet-like electrode may be formed from the negative electrode active material by rolling, or a particle electrode may be formed by compression molding.

[0134] IV, Separator

[0135] To prevent short circuits, a separator is usually placed between the positive and negative electrodes. In this case, the electrolyte of the present invention is usually used by permeating the separator.

[0136] In this application, the material, shape, thickness, porosity, and average pore diameter of the separator are not particularly limited, as long as they do not impair the effects of this application.

[0137] This application further provides an electrochemical apparatus, which includes the above-mentioned secondary battery.

[0138] The electrochemical apparatus may be a battery pack or a battery module.

[0139] This application further provides an electrical device, which includes electric vehicles, storage batteries, and the like.

[0140] The manufacturing of lithium-ion batteries will be described below, using lithium-ion batteries as an example, along with specific embodiments. However, those skilled in the art should understand that the manufacturing methods described herein are merely examples, and that other suitable manufacturing methods are within the scope of this application.

[0141] The performance evaluation of the lithium-ion battery of this application will be described below using examples and comparative examples.

[0142] Example 1

[0143] 1. Manufacturing of lithium-ion batteries

[0144] 1. Manufacturing of positive electrode sheets

[0145] A positive electrode slurry is produced by mixing the positive electrode active material, positive electrode conductive agent, and positive electrode binder in a mass ratio of 96:2:2, then adding a solvent, and uniformly coating both sides of the aluminum foil of the positive electrode current collector with the produced positive electrode slurry. Next, it is dried at 120°C, rolled, and cut to obtain a positive electrode sheet.

[0146] Here, the positive electrode active material is NCM622, the positive electrode conductive agent is carbon black, the positive electrode binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP).

[0147] 2. Manufacturing of negative electrode sheets

[0148] The volatile content is 15% and the ash content is 0.3%. The green coke of petroleum coke is crushed and pre-mixed using a roll mill, and the particle size of the crushed green coke is 10 μm.

[0149] The pulverized product is subjected to high-temperature graphitization treatment in a protective atmosphere, where the temperature is 2800-3200°C, the maximum temperature is maintained for 36 hours, and the protective atmosphere is argon gas.

[0150] In a continuous shaping system, the product is polished and shaped over 8 hours to make the surface of the material smooth and flat.

[0151] Graphite, soft carbon (the first coating material), and a solvent are mixed at a temperature of 250°C. The mixture is then vacuumed to remove the solvent, and the mixture is then heat-treated in a horizontal oven at a temperature of 650°C for 12 hours to obtain the first mixture.

[0152] The first mixture is added to an aluminum chloride solution of a specific concentration, and ammonia water is added to maintain the stability of the solution's pH. After hydrolysis over 8 hours, the solution is filtered, repeatedly washed with deionized water and alcohol, dried, and then heat-treated in a horizontal kettle at 600°C for 5 hours to obtain a composite graphite coated product coated with aluminum trioxide. Finally, the composite graphite coated product is subjected to magnetic removal screening to obtain the final graphite product.

[0153] The above-mentioned artificial graphite product, carbon black, sodium carboxymethylcellulose, styrene-butadiene rubber, and solvent are stirred in a specific ratio using a vacuum stirrer to obtain a negative electrode slurry. The manufactured negative electrode slurry is uniformly coated on both sides of the copper foil of the negative electrode current collector, and after baking and drying, it is rolled and cut to obtain a negative electrode sheet. The baking temperature is 90-110°C.

[0154] In the dried powder of the negative electrode slurry, the mass ratio of artificial graphite, carbon black, sodium carboxymethylcellulose, and styrene-butadiene rubber, calculated by mass percentage, is 96.5:1.5:1.5:0.5.

[0155] Here, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 21°, the resistance R mΩ of the negative electrode active material layer is 9 mΩ, the OI value of the negative electrode active material layer is 4.4, the quantity content of fine powder of the negative electrode active material is 20%, and the quantity content of coarse powder of the negative electrode active material is 0.

[0156] 3. Manufacturing of electrolyte

[0157] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1, and then 1 mol / L of LiPF6 is added and mixed uniformly to produce an electrolyte.

[0158] 4. Manufacturing of separators

[0159] PP film is used as a separator.

[0160] 5. Manufacturing of lithium-ion batteries

[0161] After drying the negative electrode sheet and positive electrode sheet manufactured using the above steps, they are wound together with a separator to produce an electrical core. The positive electrode aluminum sheet and the negative electrode copper nickel plated sheet are then welded to the electrical core, and the welded electrical core is packaged in a perforated aluminum plastic film. Finally, an electrolyte solution is injected and the chemical conversion is performed to produce a secondary battery.

[0162] 2. Test Method

[0163] 1. Test and calculation methods for non-Faraday charge quantities

[0164] S1. Assemble the negative electrode sheet into a button cell, and perform a cyclic Voltamospectroscopy test on the button cell to obtain the UV potential range of the button cell.

[0165] In step S2, the potential range UV of the button cell in step S1 is selected, and a linear scanning Voltamo method test is performed on the button cell to detect the scanning speed-voltage graph and voltage-current graph. Based on the voltage-current graph, the potential range ΔUV of the negative electrode active material layer is obtained, where the scanning direction is from low potential to high potential.

[0166] In step S3, in conjunction with Figure 1, a scan rate-current scatter plot is detected based on step S2, and the non-Faraday capacitance Cdl nF of the negative electrode sheet is obtained based on the scan rate-current scatter plot.

[0167] In step S4, based on the potential range ΔUV and non-Fraday capacitance Cdl nF obtained from steps S2 and S3, the non-Fraday charge Q is calculated using the formula Q = Cdl × ΔU.

[0168] Here, the non-Faraday charge QC of the negative electrode sheet is 0.28C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 1.4nF, and the potential range ΔUV of the negative electrode active material layer is 0.2V.

[0169] 2. Test method for the cycle performance of lithium-ion batteries

[0170] The lithium-ion battery is left standing at 25°C for 30 minutes, then discharged at a constant current of 1C, left standing for 10 minutes, then charged at a constant current and constant voltage of 1C, left standing for 10 minutes, and finally a full charge-full discharge cycle test is performed. This is repeated until the lithium-ion battery's capacity exceeds 80% of its initial capacity, and the number of cycles is recorded.

[0171] 3. Test method for high-temperature circulation performance of lithium-ion batteries

[0172] A lithium-ion battery is left to stand at 25°C for 30 minutes, then discharged at a constant current of 1C, left to stand for 10 minutes, then charged at a constant current and constant voltage of 1C, left to stand for 10 minutes, and finally a full charge-full discharge cycle test is performed. The initial charge / discharge capacity and the discharge capacity after 2000 cycles are recorded, and the capacity retention rate is calculated as: Discharge capacity after 2000 cycles / Initial discharge capacity × 100%.

[0173] Example 2

[0174] Example 2 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0175] The non-Faraday charge QC of the negative electrode sheet is 0.07C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 0.7nF, the potential range ΔUV of the negative electrode active material layer is 0.1V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 35°, the resistance R mΩ of the negative electrode active material layer is 18mΩ, the OI value of the negative electrode active material layer is 5, the quantity content of fine powder of the negative electrode active material is 60%, and the quantity content of coarse powder of the negative electrode active material is 50%.

[0176] Example 3

[0177] Example 3 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0178] The non-Faraday charge QC of the negative electrode sheet is 2C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 4.0nF, the potential range ΔUV of the negative electrode active material layer is 0.5V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 22°, the resistance R mΩ of the negative electrode active material layer is 8mΩ, the OI value of the negative electrode active material layer is 2.5, the quantity content of fine powder of the negative electrode active material is 35%, and the quantity content of coarse powder of the negative electrode active material is 30%.

[0179] Example 4

[0180] Example 4 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0181] The non-Faraday charge QC of the negative electrode sheet is 0.26C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 1.3nF, the potential range ΔUV of the negative electrode active material layer is 0.2V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 20°, the resistance R mΩ of the negative electrode active material layer is 10mΩ, the OI value of the negative electrode active material layer is 4.4, the quantity content of fine powder of the negative electrode active material is 0%, and the quantity content of coarse powder of the negative electrode active material is 20%.

[0182] At the same time, in Example 4, no lithium salt additive was added to the electrolyte, the thickness Hnm of the protective film layer was 60nm, the content of the lithium salt additive in the electrolyte was X, and the thickness H of the protective film layer and the non-Faraday charge Q of the negative electrode sheet satisfied 10X·H+Q=0.26.

[0183] Example 5

[0184] Example 5 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0185] The non-Faraday charge QC of the negative electrode sheet is 2.5C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 5.0nF, the potential range ΔUV of the negative electrode active material layer is 0.5V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 10°, the resistance R mΩ of the negative electrode active material layer is 5mΩ, the OI value of the negative electrode active material layer is 2.1, the quantity content of fine powder of the negative electrode active material is 10%, and the quantity content of coarse powder of the negative electrode active material is 10%.

[0186] Example 6

[0187] Example 6 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0188] The non-Faraday charge QC of the negative electrode sheet is 0.54C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 2.7nF, the potential range ΔUV of the negative electrode active material layer is 0.2V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 25°, the resistance R mΩ of the negative electrode active material layer is 10mΩ, the OI value of the negative electrode active material layer is 4, the quantity content of fine powder of the negative electrode active material is 0%, and the quantity content of coarse powder of the negative electrode active material is 30%.

[0189] Example 7

[0190] Example 7 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0191] The non-Faraday charge QC of the negative electrode sheet is 0.78C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 3.9nF, the potential range ΔUV of the negative electrode active material layer is 0.2V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 23°, the resistance R mΩ of the negative electrode active material layer is 8mΩ, the OI value of the negative electrode active material layer is 2.5, the quantity content of fine powder of the negative electrode active material is 35%, and the quantity content of coarse powder of the negative electrode active material is 30%.

[0192] Example 8

[0193] Example 8 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0194] The non-Faraday charge QC of the negative electrode sheet is 0.96C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 4.8nF, the potential range ΔUV of the negative electrode active material layer is 0.2V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 12°, the resistance R mΩ of the negative electrode active material layer is 5mΩ, the OI value of the negative electrode active material layer is 2.2, the quantity content of fine powder of the negative electrode active material is 15%, and the quantity content of coarse powder of the negative electrode active material is 20%.

[0195] Example 9

[0196] Example 9 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0197] The non-Faraday charge QC of the negative electrode sheet is 1.11C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 3.7nF, the potential range ΔUV of the negative electrode active material layer is 0.3V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 22°, the resistance R mΩ of the negative electrode active material layer is 8mΩ, the OI value of the negative electrode active material layer is 2.4, the quantity content of fine powder of the negative electrode active material is 35%, and the quantity content of coarse powder of the negative electrode active material is 30%.

[0198] Example 10

[0199] Example 10 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, with the exception of the following differences, otherwise it is the same as Example 1.

[0200] The non-Faraday charge QC of the negative electrode sheet is 1.41C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 4.7nF, the potential range ΔUV of the negative electrode active material layer is 0.3V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 12°, the resistance R mΩ of the negative electrode active material layer is 5mΩ, the OI value of the negative electrode active material layer is 2.2, the quantity content of fine powder of the negative electrode active material is 0%, and the quantity content of coarse powder of the negative electrode active material is 20%.

[0201] Example 11

[0202] Example 11 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1, with the following differences.

[0203] The non-Faraday charge QC of the negative electrode sheet is 1.72C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 4.3nF, the potential range ΔUV of the negative electrode active material layer is 0.4V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 20°, the resistance R mΩ of the negative electrode active material layer is 6mΩ, the OI value of the negative electrode active material layer is 2.2, the quantity content of fine powder of the negative electrode active material is 35%, and the quantity content of coarse powder of the negative electrode active material is 25%.

[0204] Example 12

[0205] Example 12 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0206] The non-Faraday charge QC of the negative electrode sheet is 0.12C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 0.4nF, the potential range ΔUV of the negative electrode active material layer is 0.3V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 37°, the resistance R mΩ of the negative electrode active material layer is 15mΩ, the OI value of the negative electrode active material layer is 5.5, the quantity content of fine powder of the negative electrode active material is 25%, and the quantity content of coarse powder of the negative electrode active material is 25%.

[0207] Example 13

[0208] Example 13 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0209] The non-Faraday charge QC of the negative electrode sheet is 0.225C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 2.5nF, the potential range ΔUV of the negative electrode active material layer is 0.09V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 20°, the resistance R mΩ of the negative electrode active material layer is 8mΩ, the OI value of the negative electrode active material layer is 6.5, the quantity content of fine powder of the negative electrode active material is 10%, and the quantity content of coarse powder of the negative electrode active material is 15%.

[0210] Example 14

[0211] Example 14 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1, with the following differences.

[0212] The non-Faraday charge QC of the negative electrode sheet is 0.45C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 1.5nF, the potential range ΔUV of the negative electrode active material layer is 0.3V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 25°, the resistance R mΩ of the negative electrode active material layer is 10mΩ, the OI value of the negative electrode active material layer is 7, the quantity content of fine powder of the negative electrode active material is 25%, and the quantity content of coarse powder of the negative electrode active material is 0%.

[0213] Example 15

[0214] Example 15 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1, with the following differences.

[0215] The non-Faraday charge QC of the negative electrode sheet is 0.12C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 1.2nF, the potential range ΔUV of the negative electrode active material layer is 0.1V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 22°, the resistance R mΩ of the negative electrode active material layer is 8mΩ, the OI value of the negative electrode active material layer is 9, the quantity content of fine powder of the negative electrode active material is 0%, and the quantity content of coarse powder of the negative electrode active material is 22%.

[0216] Example 16

[0217] Example 16 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0218] In the electrolyte, the type of lithium salt additive is LiFSI, the content X of the lithium salt additive in the electrolyte is 1%, the thickness Hnm of the protective film layer is 120nm, and the content X of the lithium salt additive in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=12.26.

[0219] Example 17

[0220] Example 17 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0221] In the electrolyte, the type of lithium salt additive is LiFSI, the lithium salt additive content X in the electrolyte is 0.5%, the thickness Hnm of the protective film layer is 100nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=5.26.

[0222] Example 18

[0223] Example 18 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0224] In the electrolyte, the type of lithium salt additive is LiFSI, the lithium salt additive content X in the electrolyte is 1.5%, the thickness Hnm of the protective film layer is 150nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=22.76.

[0225] Example 19

[0226] Example 19 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0227] In the electrolyte, the type of lithium salt additive is LiFSI, the lithium salt additive content X in the electrolyte is 2%, the thickness Hnm of the protective film layer is 180nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=36.26.

[0228] Example 20

[0229] Example 20 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise being the same as Example 4.

[0230] In the electrolyte, the type of lithium salt additive is LiFSI, the lithium salt additive content X in the electrolyte is 2.5%, the thickness Hnm of the protective film layer is 200nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=50.26.

[0231] Example 21

[0232] Example 21 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0233] The type of lithium salt additive in the electrolyte is LiPO2F2, the content X of the lithium salt additive in the electrolyte is 1%, the thickness Hnm of the protective film layer is 110nm, and the content X of the lithium salt additive in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=11.26.

[0234] Example 22

[0235] Example 22 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0236] The type of lithium salt additive in the electrolyte is LiPO2F2, the content X of the lithium salt additive in the electrolyte is 0.8%, the thickness Hnm of the protective film layer is 120nm, and the content X of the lithium salt additive in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=5.26.

[0237] Example 23

[0238] Example 23 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, but is otherwise identical to Example 4, with the following differences.

[0239] The type of lithium salt additive in the electrolyte is LiBF4, the content X of the lithium salt additive in the electrolyte is 0.5%, the thickness Hnm of the protective film layer is 120nm, and the content X of the lithium salt additive in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H+Q=5.26.

[0240] Example 24

[0241] Example 24 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0242] In the electrolyte, the type of lithium salt additive is LiFSI + LiPO2F2, the LiFSI content in the electrolyte is 0.5%, the LiPO2F2 content in the electrolyte is 0.3%, the thickness Hnm of the protective film layer is 120nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H + Q = 9.86.

[0243] Example 25

[0244] Example 25 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0245] In the electrolyte, the type of lithium salt additive is LiFSI + LiPO2F2, the LiFSI content in the electrolyte is 0.5%, the LiPO2F2 content in the electrolyte is 0.5%, the thickness Hnm of the protective film layer is 150nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H + Q = 15.26.

[0246] Example 26

[0247] Example 26 involves manufacturing a lithium-ion battery using the method of Example 4 and testing the lithium-ion battery using the test method of Example 4, with the exception of the following differences, otherwise it is the same as Example 4.

[0248] In the electrolyte, the type of lithium salt additive is LiFSI + LiBF4, the LiFSI content in the electrolyte is 0.3%, the LiBF4 content in the electrolyte is 0.2%, the thickness Hnm of the protective film layer is 130nm, and the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Faraday charge Q of the negative electrode sheet satisfy 10X·H + Q = 6.75.

[0249] Comparative Example 1

[0250] Comparative Example 1 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0251] The non-Faraday charge QC of the negative electrode sheet is 3C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 6.0nF, the potential range ΔUV of the negative electrode active material layer is 0.5V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 45°, the resistance R mΩ of the negative electrode active material layer is 5mΩ, the OI value of the negative electrode active material layer is 10, the quantity content of fine powder of the negative electrode active material is 0%, and the quantity content of coarse powder of the negative electrode active material is 65%.

[0252] Comparative Example 2

[0253] Comparative Example 2 involves manufacturing a lithium-ion battery using the method of Example 1 and testing the lithium-ion battery using the test method of Example 1, but is otherwise identical to Example 1 except for the following differences.

[0254] The non-Faraday charge QC of the negative electrode sheet is 0.02C, the non-Faraday capacitance Cdl nF of the negative electrode sheet is 0.2nF, the potential range ΔUV of the negative electrode active material layer is 0.1V, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface is 10°, the resistance R mΩ of the negative electrode active material layer is 25mΩ, the OI value of the negative electrode active material layer is 8, the quantity content of fine powder of the negative electrode active material is 85%, and the quantity content of coarse powder of the negative electrode active material is 65%.

[0255] III. Test Results

[0256] Table 1 shows the effects of the non-Faraday charge QC of the negative electrode sheet, the non-Faraday capacitance Cdl nF of the negative electrode sheet, the potential range ΔUV of the negative electrode active material layer, the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface, the resistance R mΩ of the negative electrode active material layer, the OI value of the negative electrode active material layer, the quantity content of fine powder of the negative electrode active material, and the quantity content of coarse powder of the negative electrode active material on the room temperature cycle performance and high temperature cycle performance of the lithium-ion battery.

[0257] [Table 1]

[0258] As a result, by controlling the non-Faraday charge QC of the negative electrode sheet within the range of 0.05C to 2.5C, the non-Faraday capacitance Cdl nF of the negative electrode sheet within the range of 0.5nF to 5nF, the potential range ΔUV of the negative electrode active material layer within the range of 0.1V to 0.5V, the surface contact angle θ of the negative electrode active material layer with respect to the electrolyte within the range of 10 to 40°, the resistance R mΩ of the negative electrode active material layer within the range of 5mΩ to 20mΩ, the OI value of the negative electrode active material layer within the range of 2 to 15, the quantity content of fine powder in the negative electrode active material within the range of 0 to 80%, and the quantity content of coarse powder in the negative electrode active material within the range of 0 to 60%, the cycle life of the lithium-ion battery can be significantly improved.

[0259] Furthermore, by controlling the Faraday capacitance Cdl nF of the negative electrode sheet within the range of 1.4 nF to 4.3 nF, controlling the contact angle θ of the negative electrode active material layer with respect to the electrolyte surface within the range of 12 to 35°, controlling the resistance R mΩ of the negative electrode active material layer within the range of 5 mΩ to 12 mΩ, controlling the OI value of the negative electrode active material layer within the range of 2 to 10, controlling the quantity content of fine powder in the negative electrode active material within the range of 0 to 40%, and controlling the quantity content of coarse powder in the negative electrode active material within the range of 0 to 30%, the cycle life of the lithium-ion battery can be further improved.

[0260] Table 2 shows the effects on the room temperature cycle performance and high temperature cycle performance of a lithium-ion battery when the relationship between the type of lithium salt additive in the electrolyte, the content of the lithium salt additive in the electrolyte X, the thickness of the protective film layer Hnm, the content of the lithium salt additive in the electrolyte X, the thickness of the protective film layer H, and the non-Faraday charge Q of the negative electrode sheet satisfies 10X·H+Q.

[0261] [Table 2]

[0262] As a result, by controlling the type of lithium salt additive in the electrolyte to one or more of lithium tetrafluoroborate (abbreviated as LiBF4), lithium bis(oxalato)borate (abbreviated as LiBOB), lithium difluorophosphate (abbreviated as LiPO2F2), lithium bis(trifluoromethanesulfonimide) (abbreviated as LiTFSI), and lithium bis(fluorosulfonyl)imide (abbreviated as LiFSI), controlling the lithium salt additive content X in the electrolyte to within the range of 0.1% to 2%, controlling the thickness Hnm of the protective film layer to within the range of 5nm to 180nm, and controlling the relationship 10X·H+Q between the lithium salt additive content X in the electrolyte, the thickness H of the protective film layer, and the non-Fraday amount Q of the negative electrode sheet to within the range of 0.4 to 36, the cycle life of the lithium-ion battery can be significantly improved.

[0263] The explanations provided in the steps above are intended only to aid in understanding the method, structure, and core idea of ​​this application. Those skilled in the art should understand that many improvements and modifications can be made to this application without departing from its principles, and these too fall within the scope of protection of the claims of this application.

Claims

1. It includes a positive electrode sheet, a separator, an electrolyte, and a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer comprises one or more of the following: artificial graphite, natural graphite, soft carbon, hard carbon, amorphous carbon, carbon fiber nanotubes, or mesocarbon microspheres, and the negative electrode active material layer has a two-layer coating structure, the two-layer coating structure comprising an inner soft carbon coating layer and an outer inorganic coating layer. Here, the non-Faraday charge of the negative electrode sheet is QC, satisfying 0.05 ≤ Q ≤ 2.5, and Q = Cdl × ΔU. Cdl mF is the non-Faraday capacitance of the negative electrode sheet, ΔUV is the potential range of the negative electrode active material layer. Secondary battery.

2. The Cdl satisfies 0.5 ≤ Cdl ≤ 5, and the ΔU satisfies 0.1 ≤ ΔU ≤ 0.

5. The secondary battery according to claim 1.

3. The contact angle of the negative electrode active material layer with respect to the surface of the electrolyte is θ, and θ satisfies 10° ≤ θ ≤ 40°. The secondary battery according to claim 1 or 2.

4. The resistance of the negative electrode active material layer is RmΩ, satisfying 5 ≤ R ≤ 20. The secondary battery according to claim 1 or 2.

5. The OI value of the negative electrode active material layer is between 2 and 15. The secondary battery according to claim 1 or 2.

6. The negative electrode active material layer contains a negative electrode active material, the quantity content of fine powder of the negative electrode active material is 0 to 80%, and the quantity content of coarse powder of the negative electrode active material is 0 to 60%. The fine powder refers to negative electrode active material particles with a particle size of 2.2 μm or less, and the coarse powder refers to negative electrode active material particles with a particle size of 35 μm or more. The secondary battery according to claim 1 or 2.

7. The quantity content of the fine powder of the negative electrode active material is 0 to 40%. The quantity content of the coarse powder of the negative electrode active material is 0 to 30%. The secondary battery according to claim 6.

8. The electrolyte contains a lithium salt additive, and the lithium salt additive contains one or more of the following: lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonimide), and lithium bis(fluorosulfonyl)imide. The secondary battery according to claim 1 or 2.

9. In the electrolyte, the content of the lithium salt additive is X, satisfying 0.1% ≤ X ≤ 2%. The secondary battery according to claim 8.

10. The negative electrode active material layer includes a protective film layer, and the thickness of the protective film layer is H nm. Satisfying 0.4 ≤ 10X・H + Q ≤ 36, The secondary battery according to claim 1 or 2.

11. The thickness H nm of the protective film layer satisfies 5 ≤ ​​H ≤ 180. The secondary battery according to claim 10.

12. A secondary battery according to claim 1 or 2, Electrochemical apparatus.

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