Secondary battery and battery module, battery pack, and power consumption device equipped therewith

Abstract

The present invention provides a secondary battery using a thin-walled negative electrode current collector, as well as a battery module, battery pack, and power consumption device equipped therewith, which enable low cost, high energy density, high output performance, and high safety performance. [Solution] The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte. The non-aqueous electrolyte contains a compound represented by formula 1, the mass percentage of the compound represented by formula 1 is A1 (%) relative to the total mass of the non-aqueous electrolyte, the thickness of the negative electrode current collector is H1 (μm), and the compressed density of the negative electrode active material layer is P1 (g / cm³). 3 ) and the secondary battery satisfies the following conditions: H1 is 3 to 7, A1 / H1 is 0.003 to 0.40, and P1 / A1 is 1 to 90. TIFF2026082865000010.tif36134

Description

[Technical Field]

[0001] This application relates to the field of battery technology, and more specifically to secondary batteries and battery modules, battery packs, and power consumption devices equipped therewith. [Background technology]

[0002] In recent years, secondary batteries have been widely used in many fields, including energy storage and 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. With the application and widespread use of secondary batteries, the demand for higher energy density is increasing. Since copper foil current collectors do not contribute to the capacity of secondary batteries, thinning them not only reduces costs but also allows for the inclusion of more active material in a limited battery case. Therefore, thinning copper foil current collectors is one of the most effective measures to increase the energy density of secondary batteries. While thinning copper foil current collectors reduces costs and improves the energy density of secondary batteries, this method is difficult to implement industrially because it increases the internal resistance and heat generation of the battery. As a result, current secondary batteries cannot combine low cost, high energy density, high output performance, and high safety performance. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] The object of this application is to provide a secondary battery, a battery module, a battery pack, and a power consumption device equipped therewith, which enable a secondary battery using a thinned negative electrode current collector to combine low cost, high energy density, high output performance, and high safety performance. [Means for solving the problem]

[0004] A first aspect of the present invention is a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector, the non-aqueous electrolyte comprises a compound represented by formula 1, the mass percentage of the compound represented by formula 1 is A1 (%) relative to the total mass of the non-aqueous electrolyte, the thickness of the negative electrode current collector is H1 (μm), and the compressed density of the negative electrode active material layer is P1 (g / cm³). 3 The present invention provides a secondary battery that satisfies the following conditions: H1 is 3 to 7, A1 / H1 is 0.003 to 0.40, and P1 / A1 is 1 to 90. [ka] (X and Y each independently represent a fluorine atom, or at least one of the group consisting of partially fluorinated or fully fluorinated C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and at least one of X and Y represents a fluorine atom.)

[0005] As a result of research conducted by the inventors of this invention, in a secondary battery using a thinned negative electrode current collector, the non-aqueous electrolyte contains a compound represented by formula 1, and the secondary battery satisfies the conditions that A1 / H1 is 0.003 to 0.40 and P1 / A1 is 1 to 90, by adjusting the content A1 (%), the thickness H1 (μm) of the negative electrode current collector, and the compressed density P1 (g / cm³) of the negative electrode active material layer. 3 By controlling the relationship with (), secondary batteries can combine low cost, high energy density, high output performance, and high safety performance.

[0006] In any embodiment of the present invention, A1 / H1 is selectively 0.003 to 0.1, and more selectively 0.003 to 0.08. This makes it possible to provide the secondary battery with both high output performance and high safety performance.

[0007] In any embodiment of the present invention, P1 / A1 is selectively 3 to 90, and more selectively 5 to 90. This makes it possible to provide the secondary battery with both high output performance and high safety performance.

[0008] In any embodiment of the present application, the thickness of the positive electrode current collector is H2 (μm), the elongation at break of the positive electrode current collector is Q (%), and the compressed density of the positive electrode active material layer is P2 (g / cm³). 3 ) and the secondary battery satisfies the following conditions: H2 is 4 to 14, A1 / H2 is 0.0015 to 0.20, Q+A1 is 1 to 4, and P2 / A1 is 2 to 340.

[0009] Further research by the inventors of this invention has revealed the following findings: the compound content A1 (%) represented by formula 1, the thickness H2 (μm) of the positive electrode current collector, the elongation at break Q (%) of the positive electrode current collector, and the compressive density P2 (g / cm³) of the positive electrode active material layer. 3 Furthermore, if the following conditions are met, such that H2 is 4-14, A1 / H2 is 0.0015-0.20, Q+A1 is 1-4, and P2 / A1 is 2-340, then thinning the positive electrode current collector contributes to improving the adverse effects on the output performance, safety performance, and processing performance of the secondary battery.

[0010] In any embodiment of the present invention, A1 / H2 is selectively 0.002 to 0.05, and more selectively 0.01 to 0.05. This improves the strength of the positive electrode current collector, improves the processing performance of the positive electrode sheet, and contributes to reducing and even avoiding the occurrence of rupture. It also contributes to providing the secondary battery with high output performance and high safety performance.

[0011] In any embodiment of the present invention, Q+A1 is selectively 1.5 to 3.5, and more selectively 2.0 to 3.5. This improves the strength of the positive electrode current collector, improves the processing performance of the positive electrode sheet, and contributes to reducing and even avoiding the occurrence of rupture. It also contributes to providing the secondary battery with high output performance and high safety performance.

[0012] In any embodiment of the present invention, P2 / A1 is selectively 5 to 340, and more selectively 10 to 340. This is advantageous for improving the output performance and safety performance of the secondary battery.

[0013] In any embodiment of the present application, A1 is selectively 0.02 to 1.6, and more selectively 0.02 to 0.5. This improves defects such as deterioration of output performance, increased safety risks, and deterioration of processing performance caused by thinning the negative and positive electrode current collectors.

[0014] In any embodiment of the present application, P1 is selectively 1.4 to 1.8, and more selectively 1.55 to 1.75. This contributes to increasing the energy density of the secondary battery.

[0015] In any embodiment of the present invention, P2 is selectively 3.2 to 3.7, and more selectively 3.4 to 3.7. This contributes to increasing the energy density of the secondary battery.

[0016] In any embodiment of this application, Q is selectively 0.5 to 3.5, and more selectively 1.5 to 3.5. This results in a positive electrode current collector with high strength and excellent workability, and less prone to rupture.

[0017] In any embodiment of the present application, the first lithium salt comprising lithium hexafluorophosphate is optionally further included. The mass percentage of the lithium hexafluorophosphate is A2 (%) relative to the total mass of the non-aqueous electrolyte. Selectively, A2 / A1 is 5 to 650, and more selectively, 15 to 300. This contributes to further improving the capacity retention rate of the secondary battery while mitigating problems such as degradation of output performance and increased safety risks due to the thinning of the current collector.

[0018] In any embodiment of the present application, A2 is optionally 6 to 14.

[0019] In any embodiment of the present application, the first lithium salt optionally comprises a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide. The mass percentage of lithium hexafluorophosphate is A2 (%) relative to the total mass of the non-aqueous electrolyte, and the mass percentage of lithium bisfluorosulfonylimide is A3 (%) relative to the total mass of the non-aqueous electrolyte. Selectively, A2 is between 6 and 14, and A3 is greater than 0 and less than or equal to 5.

[0020] Selectively, the A3 / A2 ratio is 0.8 or less, and more selectively, 0.05 to 0.3. This contributes to the formation of an interfacial film with lower resistance.

[0021] Selectively, A2 / A1 is 5-650, and more selectively, 15-300. This helps to improve the capacity retention rate of secondary batteries while mitigating problems such as the degradation of output performance and increased safety risks caused by thinning the current collector.

[0022] In any embodiment of the present application, the non-aqueous electrolyte optionally further comprises a second lithium salt comprising at least one of lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate. The total mass content of the second lithium salt in the non-aqueous electrolyte is A4 (%) relative to the total mass of the non-aqueous electrolyte. Selectively, A4 is 5 or less, and more selectively, 2 or less. The second lithium salt can, as an auxiliary lithium salt, further play a role in improving the interfacial performance of the positive and / or negative electrodes, or in improving the ionic conductivity or thermal stability of the non-aqueous electrolyte.

[0023] In any embodiment of the present application, the second lithium salt optionally comprises lithium difluorophosphate, and optionally the mass ratio α of lithium difluorophosphate to lithium hexafluorophosphate is 0.01 to 0.15, and more optionally 0.01 to 0.1. Lithium difluorophosphate has high electrochemical stability, improves the ionic conductivity of the non-aqueous electrolyte, improves the properties of the positive and negative electrode interface films, and contributes to the production of safe and low-resistance positive and negative electrode interface films. This effectively reduces the decomposition of the non-aqueous electrolyte and further improves the output performance and safety performance of the secondary battery.

[0024] In any embodiment of the present application, the non-aqueous electrolyte optionally further comprises a cyclic carbonate compound. The mass percentage of the cyclic carbonate compound is B1(%) relative to the total mass of the non-aqueous electrolyte. Optionally, B1 is 0.5 to 20, and more selectively, 15 to 18.

[0025] In any embodiment of the present invention, B1 / 20+A1 is selectively 1 to 3, and more selectively 1 to 2. This contributes to further improving the capacity retention rate of the secondary battery while mitigating problems such as degradation of output performance and increased safety risks due to thinning of the current collector.

[0026] In any embodiment of the present application, optionally, the cyclic carbonate compound contains at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, and vinyl ethylene carbonate.

[0027] In any embodiment of the present application, optionally, the non-aqueous electrolyte further contains fluoroethylene carbonate. Its mass percentage is C1 (%) with respect to the total mass of the non-aqueous electrolyte. Optionally, 0 < C1 ≤ 2.5, more selectively, 0 < C1 ≤ 2.0. Thereby, the cycle performance of the secondary battery can be effectively improved.

[0028] In any embodiment of the present application, optionally, 0.25 ≤ C1 / A1 ≤ 25, more selectively, 0.5 ≤ C1 / A1 ≤ 10. Thereby, while improving problems such as deterioration of output performance and increase in safety risks due to thinning of the current collector, the cycle performance of the secondary battery is further improved.

[0029] In any embodiment of the present application, optionally, the non-aqueous electrolyte further contains a dehydration additive containing at least one of hexamethyldisilazane and tris(trimethylsilyl) phosphate. Optionally, the mass percentage of the dehydration additive is 2% or less, more selectively 0.05% - 1% with respect to the total mass of the non-aqueous electrolyte. This contributes to further improving the output performance, storage performance, and safety performance of the secondary battery.

[0030] In any embodiment of the present application, optionally, both X and Y represent fluorine atoms.

[0031] In any embodiment of the present application, optionally, among X and Y, one represents a fluorine atom, and the other represents at least one of C1 - C5 alkyl, C2 - C5 alkenyl, C2 - C5 alkynyl, phenyl, phenoxy, C1 - C5 alkoxy, C2 - C5 alkenyloxy, and C2 - C5 alkynyloxy that is partially fluorinated or fully fluorinated.

[0032] In any embodiment of the present application, optionally, one of X and Y represents a fluorine atom, and the other represents at least one of the group consisting of partially fluorinated or fully fluorinated methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadienyl, ethynyl, propynyl, phenyl, methoxy, ethoxy, proxy, vinyloxy, propenyloxy, ethynyloxy, propynyloxy, and phenoxy.

[0033] The presence of fluorine atoms is advantageous for forming thinner positive and / or negative electrode interface films, contributes to the uniform transport of lithium ions, and effectively suppresses the formation of lithium dendrites.

[0034] In any embodiment of the present application, the compound represented by formula 1 optionally includes at least one of the following compounds. [ka]

[0035] In any embodiment of the present application, the negative electrode current collector is optionally made of copper foil or copper alloy foil.

[0036] In any embodiment of the present application, the positive electrode current collector is optionally made of aluminum foil or aluminum alloy foil.

[0037] A second aspect of the present application provides a battery module including the secondary battery described in the first aspect of the present application.

[0038] A third aspect of the present application provides a battery pack comprising one of the secondary battery described in the first aspect of the present application and one of the battery modules described in the second aspect.

[0039] A fourth aspect of the present application provides a power consumption device comprising at least one of the secondary battery described in the first aspect of the present application, the battery module described in the second aspect, and the battery pack described in the third aspect.

[0040] The battery module, battery pack, and power consumption device of the present invention include a secondary battery according to the present invention, and therefore have at least the same advantages as the aforementioned secondary battery. [Brief explanation of the drawing]

[0041] To further illustrate the technical concept of the embodiments of this application, the drawings used in the embodiments of this application are briefly described below. Clearly, the drawings described below represent only a part of the embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without requiring any creative effort. [Figure 1] This is a schematic diagram of one embodiment of the secondary battery of the present invention. [Figure 2] Figure 1 is a schematic diagram of an exploded view of an embodiment of a secondary battery. [Figure 3] This is a schematic diagram of one embodiment of the battery module of the present invention. [Figure 4] This is a schematic diagram of one embodiment of the battery pack of the present invention. [Figure 5] Figure 4 is a schematic exploded view of an embodiment of the battery pack shown. [Figure 6] This is a schematic diagram of one embodiment of a power consumption device that includes the secondary battery of the present invention as a power source. [Explanation of Symbols]

[0042] In drawings, the proportions are not always accurate to the actual values. 1 Battery pack 2 Upper box 3 Lower box 4 Battery Modules 5 Secondary battery 51 cases 52 Electrode Assembly 53 Cover Plate [Modes for carrying out the invention]

[0043] Hereinafter, embodiments specifically disclosing the secondary battery, battery module, battery pack, and power consumption device equipped therewith according to the present application will be described in detail with appropriate reference to the drawings. However, some unnecessary details may be omitted. For example, detailed explanations of known matters or redundant explanations of the same structure may be omitted. This is to avoid the following description becoming unnecessarily verbose and to facilitate understanding by those skilled in the art. Furthermore, the 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 claims.

[0044] The “range” disclosed herein is limited in the form of a lower and upper limit, and a given range is limited by selecting a lower and upper limit that define the boundary of a particular range. The range thus defined may or may not include end values, and any combination is possible, that is, any lower limit and any upper limit can be combined to form a single range. For example, if the ranges 60-120 and 80-110 are given for a particular parameter, it can be understood that the ranges 60-110 and 80-120 are also expected. Also, if the minimum range values ​​are given as 1 and 2, and the maximum range values ​​are given as 3, 4 and 5, then the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all expected. In this application, unless otherwise specified, the range “a-b” represents an abbreviated expression for any combination of real numbers between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is an abbreviation of combinations of these numbers. Also, when a parameter is described as being an integer of 2 or more, it is disclosed that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and any embodiments of this Application can be combined to form new technical solutions. Such technical solutions will be deemed to be included in the disclosures of this Application.

[0046] Unless otherwise specified, all technical features and any technical features of this application can be combined to form new technical concepts. Such technical concepts shall be deemed to be included in the disclosures of this application.

[0047] Unless otherwise specified, all steps of this invention may be performed sequentially, randomly, or selectively sequentially. For example, if the method includes steps (a) and (b), it indicates that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may further include step (c), it indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b).

[0048] Unless otherwise specified, the terms "contains," "possesses," and "equip" as used in this application mean open-ended, or they may also mean closed-ended. For example, the terms "contains," "possesses," and "equip" can mean further "contains," "possesses," or "equips" other components not listed, or "contains," "possesses," or "equips" only the listed components.

[0049] Unless otherwise specified, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0050] Throughout this specification, substituents of compounds are disclosed in groups or ranges. Such descriptions are explicitly expected to include individual subcombinations of members of these groups and ranges. For example, the term “C1-C6 alkyl” alone is explicitly expected to disclose alkyls of C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, and C5-C6.

[0051] In this application, the terms "multiple" and "multiple types" mean two or more.

[0052] In this application, the thickness of the current collector and the active material layer has meanings known in the art and can be tested using methods known in the art. For example, they can be measured using a spiral micrometer.

[0053] In this application, the compressive density of the active material layer has a meaning known in the art and can be tested using methods known in the art. The compressive density of the active material layer = surface density of the active material layer / thickness of the active material layer. The surface density of the active material layer has a meaning known in the art and can be tested using methods known in the art, such as cutting an electrode sheet coated on one side and cold-pressed (if it is an electrode sheet coated on both sides, the active material layer on one side may be wiped off first), measuring its weight and recording it as M1, then wiping off the active material layer of the electrode sheet whose weight was measured, measuring the weight of the current collector and recording it as M0, and then calculating the surface density of the active material layer = (M1 - M0) / S0.

[0054] In this application, the elongation at break of the positive electrode current collector refers to the elongation at break at room temperature.

[0055] Copper foil current collectors are an essential component of secondary batteries, and thinning them remains one of the most effective measures to further increase the energy density of secondary batteries. While thinning copper foil current collectors can reduce the cost and improve the energy density of secondary batteries, this method is difficult to implement industrially. The main reasons are as follows: Firstly, thinning the copper foil current collector increases the resistance of the copper foil, which increases the internal resistance of the battery and reduces its output performance. Secondly, since copper foil is a good thermal conductor, thinning it increases the amount of heat generated in the secondary battery, making heat dissipation difficult, which increases the potential safety risk of the secondary battery.

[0056] Furthermore, high-power batteries require a large discharge current during use, resulting in high heat generation during discharge. This significantly increases the decomposition reaction of the non-aqueous electrolyte at the positive and negative electrode interfaces under high temperatures. As a result, the resistance at both the positive and negative electrode interfaces increases dramatically, reducing the output performance of the secondary battery. Currently, one common countermeasure to obtain high-power batteries is to increase the thickness of the copper foil current collector.

[0057] Therefore, currently, methods for increasing the energy density of secondary batteries by thinning the negative electrode current collector still face many difficulties in terms of practical application, such as degradation of output performance, increased safety risks, and degradation of processing performance.

[0058] The inventors of this invention were surprised to discover that by employing an appropriate non-aqueous electrolyte, problems such as the deterioration of output performance and the increase in safety risks caused by thinning the negative electrode current collector can be solved. As a result, secondary batteries can combine low cost, high energy density, high output performance, and high safety performance.

[0059] Specifically, the embodiments of the present invention provide a secondary battery.

[0060] A secondary battery, also called a rechargeable battery or storage battery, is a battery that can be used continuously by activating the active material through charging after discharge. The secondary battery of this application may be a lithium secondary battery, and in particular a lithium-ion secondary battery. The secondary battery includes an electrode assembly, a non-aqueous electrolyte, and an outer casing. The outer casing encloses the electrode assembly and the non-aqueous electrolyte. The electrode assembly usually includes a positive electrode sheet, but may further include a negative electrode sheet and a separator. The separator is provided between the positive electrode sheet and the negative electrode and primarily serves to prevent short circuits between the positive and negative electrodes and to allow lithium ions to pass through. In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be assembled into an electrode assembly by a winding process or a lamination process.

[0061] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two corresponding surfaces in its thickness direction, and the positive electrode active material layer is provided on either or both of the two opposing surfaces of the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode active material layer is provided on either or both of the two opposing surfaces of the negative electrode current collector. During charging and discharging of the secondary battery, lithium ions reciprocate between the positive electrode sheet and the negative electrode sheet for insertion and removal. The non-aqueous electrolyte includes a lithium salt and an organic solvent, and plays a role in transporting lithium ions between the positive electrode sheet and the negative electrode sheet.

[0062] In the secondary battery of the present invention, the non-aqueous electrolyte contains a compound represented by formula 1. Each of X and Y independently represents a fluorine atom, or at least one of the group consisting of partially fluorinated or fully fluorinated C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and at least one of X and Y represents a fluorine atom. [ka]

[0063] The mass percentage of the compound represented by formula 1 is A1 (%) relative to the total mass of the non-aqueous electrolyte, the thickness of the negative electrode current collector is H1 (μm), and the compressed density of the negative electrode active material layer is P1 (g / cm³). 3 ) and the secondary battery satisfies the following conditions: H1 is 3 to 7, A1 / H1 is 0.003 to 0.40, and P1 / A1 is 1 to 90.

[0064] In this application, the thickness H1 (μm) of the negative electrode current collector satisfies 3 to 7, and optionally, H1 may be 3 to 6.5, 3 to 6, 3 to 5.5, or 3 to 5.

[0065] As a result of research conducted by the inventors of this invention, in a secondary battery using a thinned negative electrode current collector, the non-aqueous electrolyte contains a compound represented by formula 1, and the secondary battery satisfies the conditions that A1 / H1 is 0.003 to 0.40 and P1 / A1 is 1 to 90, by considering the content A1 (%), the thickness H1 (μm) of the negative electrode current collector, and the compressed density P1 (g / cm³) of the negative electrode active material layer. 3 By controlling the relationship with (), secondary battery performance can be achieved with low cost, high energy density, high output performance, and high safety performance.

[0066] Although the mechanism is unknown, the inventors of this invention posit that there are several possible causes.

[0067] Firstly, the molecular structure of the compound represented by Equation 1 contains fluorine atoms, and these fluorine atoms are preferentially reduced on the surface of the negative electrode active material over organic solvents. Furthermore, the reduction products have low resistance properties, which is advantageous for forming a low-resistance negative electrode interface film. On the other hand, the B atoms in the molecular structure of the compound represented by Equation 1 readily bond strongly with inorganic components such as LiF in the negative electrode interface film. This accelerates lithium ion transport, significantly reducing the internal resistance of the battery, thereby providing the secondary battery with both high energy density and high output performance, and enabling high-current discharge.

[0068] Secondly, the compound represented by Equation 1 itself has high thermal stability, superior to, for example, ordinary LiPF6, which is advantageous in improving the overall heat resistance of the non-aqueous electrolyte. Furthermore, since the compound represented by Equation 1 is less sensitive to water than LiPF6, it is advantageous in improving the water resistance of the non-aqueous electrolyte, reducing the formation of HF, and lowering the acidity of the non-aqueous electrolyte. Therefore, the non-aqueous electrolyte of this application has high thermal stability and high electrochemical stability, thereby reducing the decomposition of the non-aqueous electrolyte at high temperatures and lowering the internal resistance of the battery. Also, as can be seen from Joule's law, the amount of heat generated by a secondary battery is directly related to the internal resistance of the battery, so when the internal resistance of the battery decreases, the amount of heat generated by the secondary battery also decreases. As a result, the secondary battery has high energy density, high output performance, and high safety performance.

[0069] Thirdly, to the inventors' surprise, the anions in the compound represented by formula 1 have a large radius and are easily reduced. Therefore, the lithium ions dissociated from their molecular structure can further become active lithium ions, which can contribute to the capacity and are advantageous in further improving the energy density of the secondary battery.

[0070] Therefore, when the non-aqueous electrolyte contains the compound represented by Formula 1, it contributes to improving the output performance and safety of the secondary battery by forming a low-resistance interfacial film on the surface of the negative electrode active material, and also contributes to increasing the number of active lithium ions and providing a portion of the capacity. However, as further research by the inventors of the present invention has shown, in order to reduce the adverse effects on output performance and safety performance caused by thinning the negative electrode current collector, and to enable the secondary battery to combine low cost, high energy density, high output performance, and high safety performance, the content of the compound represented by Formula 1 must be appropriately combined with the thickness of the negative electrode current collector and the compressed density of the negative electrode active material layer.

[0071] In this application, the content A1 (%) of the compound represented by Formula 1 and the thickness H1 (μm) of the negative electrode current collector satisfy the condition that A1 / H1 is between 0.003 and 0.40. If A1 / H1 is less than 0.003, the negative electrode current collector is thick, the content of the compound represented by Formula 1 is low, and it is not possible to form a low-resistance negative electrode interface film. As a result, the resistance of the negative electrode interface becomes high, and the deterioration of the battery's internal resistance and heat generation due to thinning the negative electrode current collector cannot be effectively reduced. Therefore, the output performance and safety performance of the secondary battery are poor, and the compound represented by Formula 1 cannot play its role in providing active lithium ions. If A1 / H1 is greater than 0.40, the negative electrode current collector is thin, the content of the compound represented by Formula 1 is high, and as a result, the negative electrode interface film that is formed is too thick. As a result, the resistance of the negative electrode interface also becomes high, the internal resistance and heat generation of the battery increase, and the output performance and safety performance of the secondary battery deteriorate. Selectively, A1 / H1 is 0.003-0.30, 0.003-0.25, 0.003-0.20, 0.003-0.16, 0.003-0.12, 0.003-0.10, 0.003-0.08, 0.003-0.06, 0.01-0.30, 0.01-0.25, 0.01-0.20, 0.01-0.16, 0.01-0.12, 0.01-0.10, 0.01-0.08, or 0.01-0.06.

[0072] In this application, the content A1 (%) of the compound represented by Formula 1 and the compressed density P1 (g / cm³) of the negative electrode active material layer are given. 3The following conditions must be met: P1 / A1 must be between 1 and 90. This means that the compound represented by formula 1 contributes to forming a low-resistance interfacial film on the surface of the negative electrode active material, thereby promoting lithium ion transport. At the same time, it reduces the resistance of the negative electrode interface, which reduces the degradation of the battery's internal resistance and heat generation due to the thinning of the negative electrode current collector, resulting in a secondary battery that combines high output performance and high safety performance. If P1 / A1 is less than 1, the compressed density of the negative electrode active material layer is low, and the content of the compound represented by formula 1 is high, resulting in a negative electrode interfacial film that is too thick. This increases the resistance of the negative electrode interface, increases the battery's internal resistance and heat generation, and degrades the output performance and safety performance of the secondary battery. If P1 / A1 is greater than 90, the compressed density of the negative electrode active material layer is high, and the content of the compound represented by formula 1 is low. As a result, the compound represented by formula 1 that forms a low-resistance interfacial film on the surface of the negative electrode active material is insufficient, and the degradation of the battery's internal resistance and heat generation due to the thinning of the negative electrode current collector cannot be effectively reduced. Therefore, the output performance and safety performance of the secondary battery will deteriorate. Selectively, P1 / A1 is 1.5~90, 1.5~75, 1.5~50, 1.5~35, 1.5~30, 1.5~25, 1.5~20, 1.5~15, 1.5~10, 3~90, 3~75, 3~50, 3~35, 3~30, 3~25, 3~20, 3~15, 3~10, 5~90, 5~75, 5~50, 5~35, 5~30, 5~25, 5~20, 5~15, or 5~10.

[0073] In some embodiments, the negative electrode current collector is made of copper foil or copper alloy foil. The copper foil may be rolled copper foil or electrolytic copper foil. As the copper alloy foil, alloy foils such as Cu-Ag, Cu-Te, Cu-Mg, Cu-Sn, Cu-Si, Cu-Mn, Cu-Be-Co, Cu-Ti, Cu-Ni-Si, Cu-Cr, Cu-Zr, Cu-Fe, Cu-Al, Cu-Zn, and Cu-Co may be used.

[0074] In some embodiments, the thickness of the positive electrode current collector is H2 (μm). H2 is 4 to 14, but selectively, H2 may be 4 to 13, 4 to 12, 4 to 11, 4 to 10, 4 to 9, or 4 to 8.

[0075] Thinning the positive electrode current collector contributes to further improving the energy density of the secondary battery. However, when the positive electrode current collector is thinned, the resistance and the amount of heat generation increase. As a result, the output performance and safety performance of the secondary battery deteriorate. Further, when the aluminum foil current collector is thinned, its own strength decreases. Also, in order to further improve the energy density of the secondary battery, since the thinned positive electrode current collector generally has a high compression density, the positive electrode sheet is easily crushed during roll pressing. This affects the processing performance of the positive electrode sheet and the secondary battery.

[0076] As a further discovery by the inventors of the present application, the content A1 (%) of the compound represented by Formula 1, the thickness H2 (μm) of the positive electrode current collector, the elongation at break Q (%) of the positive electrode current collector, and the compression density P2 (g / cm 3 ) and further, when H2 is 4 to 14, A1 / H2 is 0.0015 to 0.20, Q + A1 is 1 to 4, and P2 / A1 is 2 to 340, thinning the positive electrode current collector contributes to improving the adverse effects on the output performance, safety performance, and processing performance of the secondary battery.

[0077] The reason is that the molecular structure of the compound represented by Formula 1 contains an oxalate group, and the oxalate group is preferentially oxidized on the surface of the positive electrode active material rather than the organic solvent. Also, since the oxidation product has low resistance characteristics, it is advantageous for the formation of a low-resistance positive electrode interface film. At the same time, the B atom in the molecular structure of the compound represented by Formula 1 is also likely to be strongly bonded to inorganic components such as LiF in the positive electrode interface film, thereby accelerating the transport of lithium ions and clearly reducing the internal resistance and heat generation amount of the battery. Further, the B-O bond in the molecular structure of the compound represented by Formula 1 is bonded to Al 3+ to form a passivation film on the surface of the positive electrode current collector, which contributes to improving the strength of the positive electrode current collector, improving the processing performance of the positive electrode sheet, reducing, and further avoiding the occurrence of rupture.

[0078] Selectively, the content A1 (%) of the compound represented by Equation 1 and the thickness H2 (μm) of the positive electrode current collector satisfy the condition that A1 / H2 = 0.0015 to 0.20. This ensures that the BO bond in the molecular structure of the compound represented by Equation 1 is Al 3+ It can be better bonded with and form a passivation film of appropriate thickness on the surface of the positive electrode current collector, thereby improving the strength of the positive electrode current collector, improving the processing performance of the positive electrode sheet, and contributing to reducing and even avoiding the occurrence of rupture. Furthermore, the following situation can be effectively avoided: When A1 / H2 is less than 0.0015, Al 3+ The compound represented by formula 1, which combines with the positive electrode current collector to form a passivation film on the surface of the positive electrode current collector, is insufficient, which may result in poor processing performance of the positive electrode sheet and secondary battery. If A1 / H2 is greater than 0.20, the content of the compound represented by formula 1 is high, which may result in an excessively thick positive electrode interface film and an increase in the resistance of the positive electrode interface. This increases the internal resistance and heat generation of the battery, degrading the output performance and safety performance of the secondary battery. More selectively, A1 / H2 is 0.002-0.15, 0.002-0.1, 0.002-0.08, 0.002-0.07, 0.002-0.06, 0.002-0.05, 0.005-0.15, 0.005-0.1, 0.005-0.08, 0.005-0.07, 0.005-0.06, 0.005-0.05, 0.01-0.15, 0.01-0.1, 0.01-0.08, 0.01-0.07, 0.01-0.06, or 0.01-0.05.

[0079] Selectively, the compound content A1 (%) represented by Equation 1 and the elongation at break Q (%) of the positive electrode current collector satisfy the condition that Q + A1 is between 1 and 4. This ensures that the BO bond in the molecular structure of the compound represented by Equation 1 is Al 3+ It can be better bonded with and form a passivation film of appropriate thickness on the surface of the positive electrode current collector, thereby improving the strength of the positive electrode current collector, improving the processing performance of the positive electrode sheet, and contributing to reducing and even avoiding the occurrence of rupture. Furthermore, the following situation can be effectively avoided: If Q+A1 is less than 1, Al 3+The compound represented by Equation 1, which combines with the positive electrode current collector to form a passivation film on the surface of the positive electrode current collector, may be insufficient. Furthermore, the ductility of the positive electrode current collector may be poor, making it prone to rupture during the roll pressing process, which may result in a deterioration of the processing performance of the secondary battery. If Q+A1 is greater than 4, the positive electrode current collector has high ductility and excellent pressure resistance, but it is susceptible to puncture and is easily destroyed by sharp objects, creating large burrs and increasing the risk of short circuits inside the battery. This may deteriorate the safety performance of the secondary battery, and if there is too much of the compound represented by Equation 1, the resulting interface film will be too thick. This may increase the resistance of the positive electrode interface, potentially affecting the output performance and safety performance of the secondary battery. More selectively, Q+A1 is 1.5~4, 1.8~4, 2.0~4, 2.2~4, 2.4~4, 2.6~4, 2.8~4, 3.0~4, 1.5~3.5, 1.8~3.5, 2.0~3.5, 2.2~3.5, 2.4~3.5, 2.6~3.5, 2.8~3.5, or 3.0~3.5.

[0080] Selectively, the content A1 (%) of the compound represented by Equation 1 and the compressed density P2 (g / cm³) of the positive electrode active material layer are considered. 3The formula satisfies the condition that P2 / A1 is between 2 and 340. This means that the compound represented by formula 1 contributes to lowering the resistance of the positive electrode interface by forming a low-resistance interfacial film on the surface of the positive electrode active material, and also contributes to better bonding of the B atoms in the molecular structure of the compound represented by formula 1 with the O atoms in the positive electrode active material. This also reduces the charge transfer resistance of the positive electrode active material and the bulk phase diffusion resistance of lithium ions, thereby reducing the internal resistance and heat generation of the battery and improving the output performance and safety performance of the secondary battery. Furthermore, the following situations can be effectively avoided: If P2 / A1 is less than 2, the formed positive electrode interfacial film may be too thick, resulting in high resistance at the positive electrode interface, high internal resistance and heat generation of the battery, and potentially poor output performance and safety performance of the secondary battery. If P2 / A1 is greater than 340, the compound represented by formula 1 that forms a low-resistance interfacial film on the surface of the positive electrode active material is insufficient, and the charge transfer resistance of the positive electrode active material and the bulk phase diffusion resistance of lithium ions are high. This increases the internal resistance and heat generation of the battery, which may degrade the output performance and safety performance of the secondary battery. More selectively, P2 / A1 is 2-200, 2-100, 2-75, 2-50, 2-35, 2-30, 2-25, 2-20, 2-15, 3.5-340, 3.5-200, 3.5-100, 3.5-75, 3.5-50, 3.5-35, 3.5-30, 3.5-25, 3.5-20, 3.5-15, 5-340, 5-200, 5-100, 5-75, 5-50, 5-35, 5-30, 5-25, 5-20, 10-340, 10-200, 10-100, 10-75, 10-50, 10-35, 10-30, 10-25, or 10-20.

[0081] Selectively, in some embodiments, the content A1 (%) of the compound represented by Formula 1, the thickness H2 (μm) of the positive electrode current collector, the elongation at break Q (%) of the positive electrode current collector, and the compressive density P2 (g / cm³) of the positive electrode active material layer are selected. 3The following conditions are further met: H2 is 4-11, A1 / H2 is 0.006-0.1, Q+A1 is 1.5-3.5, and P2 / A1 is 2-340. More selectively, the compound content A1 (%) represented by Equation 1, the thickness H2 (μm) of the positive electrode current collector, the elongation at break Q (%) of the positive electrode current collector, and the compressive density P2 (g / cm³) of the positive electrode active material layer are considered. 3 The formula further satisfies the following conditions: H2 is between 4 and 11, A1 / H2 is between 0.01 and 0.05, Q+A1 is between 1.5 and 3.5, and P2 / A1 is between 5 and 75.

[0082] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Examples of metal foils include aluminum foil or aluminum alloy foil. The composite current collector may include a polymer material substrate layer and a metal material layer formed on at least one surface of the polymer material substrate layer. For example, the metal material may be at least one selected from aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. For example, the polymer material substrate layer may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0083] In some embodiments, the positive electrode current collector is selectively made of aluminum foil or aluminum alloy foil. To improve the corrosion resistance and strength of the positive electrode current collector, aluminum foil with a purity of 99.99% or higher is selectively used. The aluminum alloy foil contains at least one element from among iron, magnesium, zinc, manganese, and silicon, in addition to aluminum. For example, the aluminum alloy foil may be Al-Fe alloy foil, Al-Mn alloy foil, or Al-Mg alloy foil. The mass percentage of aluminum in the aluminum alloy foil is selectively 95% to 99.5%, and more selectively 98% to 99.5%.

[0084] In some embodiments, the content A1 (%) of the compound represented by Formula 1 satisfies the condition that A1 is between 0.02 and 1.8. Selectively, A1 is 0.02 to 1.6, 0.02 to 1.4, 0.02 to 1.2, 0.02 to 1.0, 0.02 to 0.8, 0.02 to 0.7, 0.02 to 0.6, 0.02 to 0.5, 0.05 to 1.6, 0.05 to 1.4, 0.05 to 1.2, 0.05 to 1.0, 0.05 to 0.8, 0.05 to 0.7, 0.05 to 0.6, 0.05 to 0.5, 0.1 to 1.6, 0.1 to 1.4, 0.1 to 1.2, 0.1 to 1.0, 0.1 to 0.8, 0.1 to 0.7, 0.1 to 0.6, or 0.1 to 0.5. When the content of the compound represented by Formula 1 is within an appropriate range, a low-resistance positive electrode interface film and / or negative electrode interface film can be formed, and a passivation film of appropriate thickness can be formed on the surface of the positive electrode current collector. This improves defects such as deterioration of output performance, increased safety risks, and deterioration of processing performance caused by thinning the negative electrode current collector and positive electrode current collector.

[0085] In some embodiments, the compressive density P1 (g / cm³) of the negative electrode active material layer is... 3 The following conditions must be met: P1 must be between 1.4 and 1.8. Selectively, P1 can be between 1.4 and 1.75, 1.4 and 1.7, 1.4 and 1.65, 1.55 and 1.8, 1.55 and 1.75, 1.55 and 1.7, 1.55 and 1.65, or 1.55 and 1.6. A high compressive density within the negative electrode active material layer contributes to increasing the energy density of the secondary battery.

[0086] In some embodiments, the compressive density P2 (g / cm³) of the positive electrode active material layer is... 3 The following conditions must be met: P2 must be between 3.2 and 3.7. Selectively, P2 must be between 3.3 and 3.7, 3.4 and 3.7, 3.5 and 3.7, 3.2 and 3.6, 3.3 and 3.6, 3.4 and 3.6, or 3.5 and 3.6. When the compressive density of the positive electrode active material layer is within a high range, it contributes to increasing the energy density of the secondary battery.

[0087] In some embodiments, the elongation at break Q (%) of the positive electrode current collector satisfies the condition that Q is between 0.5 and 3.5. Selectively, Q is between 1 and 3.5, 1.5 and 3.5, 1.8 and 3.5, 2.0 and 3.5, 2.2 and 3.5, 2.4 and 3.5, 2.6 and 3.5, 2.8 and 3.5, or 3.0 and 3.5. When the elongation at break of the positive electrode current collector is within an appropriate range, the positive electrode current collector has high strength and excellent workability and is less prone to rupture.

[0088] In this application, at least one of X and Y represents a fluorine atom, and the presence of a fluorine atom is advantageous for forming a thinner positive electrode interface film and / or negative electrode interface film, contributes to uniform transport of lithium ions, and effectively suppresses the formation of lithium dendrites. In some embodiments, one of X and Y represents a fluorine atom, and the other represents at least one from the group consisting of partially fluorinated or fully fluorinated C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, phenyl, phenoxy, C1-C5 alkoxy, C2-C5 alkenyloxy, and C2-C5 alkynyloxy. Selectively, one of X and Y represents a fluorine atom, and the other represents at least one of the group consisting of partially fluorinated or fully fluorinated methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadienyl, ethynyl, propynyl, phenyl, methoxy, ethoxy, proxy, vinyloxy, propenyloxy, ethynyloxy, propynyloxy, and phenoxy.

[0089] In some embodiments, both X and Y represent fluorine atoms.

[0090] As an example, the compound represented by formula 1 above includes at least one of the following compounds. [ka] [Lithium salts]

[0091] In some embodiments, the non-aqueous electrolyte further comprises a first lithium salt. The first lithium salt includes lithium hexafluorophosphate (LiPF6), or a combination of lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSI). Because lithium hexafluorophosphate has high ionic conductivity, when its content is within an appropriate range, it improves the overall ionic conductivity of the non-aqueous electrolyte, accelerates lithium ion transport, and contributes to improving the capacity retention rate of the secondary battery. However, lithium hexafluorophosphate has poor thermal stability in high-temperature environments and decomposes at high temperatures to produce PF5. PF5 reacts with water to form HF, which corrodes the positive electrode active material and increases the gas bulge of the battery. When the non-aqueous electrolyte contains both the compound represented by formula 1 and lithium hexafluorophosphate, the compound represented by formula 1 can react with lithium hexafluorophosphate to form the compound LiPF4C2O4. This reduces the partial decomposition of lithium hexafluorophosphate and the formation of HF, resulting in a secondary battery with excellent cycle performance. The chemical formula for lithium bisfluorosulfonylimide is F2NO4S2·Li, where the nitrogen atom is linked to two electron-withdrawing sulfonyl groups. This allows for sufficient delocalization of the charge on the nitrogen atom, resulting in lithium bisfluorosulfonylimide having low lattice energy and easy dissociation. This improves the ionic conductivity of non-aqueous electrolytes and reduces their viscosity. Furthermore, lithium bisfluorosulfonylimide exhibits excellent high-temperature resistance and low water solubility, allowing it to form a thinner, lower-resistance, and more thermally stable interfacial film on the surface of the negative electrode active material. This reduces side reactions between the negative electrode active material and the non-aqueous electrolyte. However, lithium bisfluorosulfonylimide is corrosive to the positive electrode current collector, so its content should not be too high.

[0092] In some embodiments, selectively, the mass content of lithium hexafluorophosphate is A2 (%) relative to the total mass of the non-aqueous electrolyte, where A2 is 6 to 14. More selectively, A2 is 6 to 12, 6 to 10, 8 to 14, 8 to 12, or 8 to 10.

[0093] In some embodiments, selectively, the mass content of lithium bisfluorosulfonylimide is A3 (%) relative to the total mass of the non-aqueous electrolyte, where A3 is greater than 0 and 5 or less. More selectively, A3 is 0.1-2.5, 0.1-2, 0.1-1.5, 0.1-1, 0.2-2.5, 0.2-2, 0.2-1.5, 0.2-1, 0.5-2.5, 0.5-2, 0.5-1.5, or 0.5-1.

[0094] In some embodiments, A3 / A2 is selectively 0.8 or less, more selectively 0.01-0.8, 0.05-0.8, 0.1-0.8, 0.01-0.6, 0.05-0.6, 0.1-0.6, 0.01-0.4, 0.05-0.4, 0.1-0.4, 0.01-0.3, 0.05-0.3, or 0.1-0.3. This makes the non-aqueous electrolyte less prone to hydrolysis, provides higher thermal stability, and is advantageous for forming an interfacial film with lower resistance.

[0095] In some embodiments, A2 / A1 is 5 to 650 relative to the total mass of the non-aqueous electrolyte. Because lithium hexafluorophosphate has high ionic conductivity, by appropriately combining the content A1 (%) of the compound represented by formula 1 and the content A2 (%) of lithium hexafluorophosphate, it is possible to improve the capacity retention rate of the secondary battery while mitigating problems such as deterioration of output performance and increased safety risks due to thinning of the current collector. Furthermore, the following situations can be effectively avoided. When the content of lithium hexafluorophosphate is high and the content of the compound represented by formula 1 is low, a large amount of PF5 is present in the non-aqueous electrolyte, leading to increased decomposition reactions of the non-aqueous electrolyte. In addition, the interfacial film formed on the positive and / or negative electrodes by the compound represented by formula 1 lacks uniformity and density, and cannot stop corrosion of the positive electrode active material by HF and a series of subsequent side reactions. As a result, the secondary battery may have high gas and heat generation, potentially degrading its output performance, storage performance, and safety performance. When the lithium hexafluorophosphate content is low and the compound represented by formula 1 content is high, the compound represented by formula 1 does not dissociate completely in the non-aqueous electrolyte, and cations and anions are easily bonded, which can lead to a decrease in the ionic conductivity of the non-aqueous electrolyte and a deterioration in the capacity retention rate of the secondary battery. Selectively, A2 / A1 is 5-500, 5-300, 5-250, 5-200, 5-150, 5-100, 5-75, 5-50, 10-500, 10-300, 10-250, 10-200, 10-150, 10-100, 10-75, 10-50, 15-500, 15-300, 15-250, 15-200, 15-150, 15-100, 15-75, or 15-50.

[0096] In some embodiments, the non-aqueous electrolyte may further contain a second lithium salt. The second lithium salt includes at least one of lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP). The second lithium salt, as an auxiliary lithium salt, can play a role in improving the interfacial performance of the positive and / or negative electrodes, or in further improving the ionic conductivity or thermal stability of the non-aqueous electrolyte.

[0097] Selectively, the total mass content of the second lithium salt in the non-aqueous electrolyte is A4 (%) relative to the total mass of the non-aqueous electrolyte, where A4 is 5 or less, and more selectively 2 or less.

[0098] Selectively, in some embodiments, the second lithium salt includes lithium difluorophosphate (LiPO2F2), lithium tetrafluoro(oxalato)phosphate (LiTFOP), or a combination thereof, and more selectively, lithium difluorophosphate (LiPO2F2). Lithium difluorophosphate has high electrochemical stability, improves the ionic conductivity of the non-aqueous electrolyte, improves the properties of the positive and negative electrode interface films, and contributes to the creation of stable and low-resistance positive and negative electrode interface films, thereby effectively reducing the decomposition of the non-aqueous electrolyte and further improving the output performance and safety performance of the secondary battery. Selectively, the mass ratio α of lithium difluorophosphate to lithium hexafluorophosphate is 0.01 to 0.15, and selectively 0.01 to 0.1.

[0099] In some embodiments, A1+A2+A3+A4 is 10-20, and selectively 12-16. [organic solvent]

[0100] In some embodiments, the non-aqueous electrolyte contains an organic solvent. The organic solvent contains at least one of a cyclic carbonate compound, a linear carbonate compound, and a carboxylate compound. Optionally, the cyclic carbonate compound may contain at least one of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and vinylethylene carbonate (VEC). Optionally, the linear carbonate compound may contain at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Selectively, the carboxylate compound may include at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), and ethyl butyrate (EB).

[0101] Selectively, in some embodiments, the organic solvent includes at least a cyclic carbonate compound and a linear carbonate compound. When the content of lithium salts, such as lithium hexafluorophosphate, is high, the viscosity of the non-aqueous electrolyte increases, the ionic conductivity decreases, and this is unfavorable for lithium ion transport. On the other hand, cyclic carbonate compounds have a high dielectric constant, which can improve the ionic conductivity of the non-aqueous electrolyte. Linear carbonate compounds have a low viscosity, which can reduce the viscosity of the non-aqueous electrolyte. Therefore, when the organic solvent includes both cyclic carbonate compounds and linear carbonate compounds, it contributes to giving the non-aqueous electrolyte appropriate viscosity and ionic conductivity, which is advantageous for lithium ion transport.

[0102] Cyclic carbonate compounds have a high dielectric constant and can improve the ionic conductivity of non-aqueous electrolytes. However, they are prone to decomposition reactions and negatively affect the storage performance of secondary batteries, so their content must be kept within an appropriate range. In some embodiments, the mass content of the cyclic carbonate compound is B1 (%) relative to the total mass of the non-aqueous electrolyte, where B1 is greater than 0 and less than or equal to 20. Selectively, B1 is 0.5-20, 1-20, 2-20, 5-20, 10-20, 12-20, 15-20, or 15-18.

[0103] In some embodiments, the mass content of the linear carbonate compound is B2 (%) relative to the total mass of the non-aqueous electrolyte, where B2 is 45-80. Selectively, B2 is 50-80, 55-80, 60-80, or 60-75.

[0104] Carboxylate compounds have the advantages of low viscosity and high dielectric constant, and when used in non-aqueous electrolytes, they contribute to giving the non-aqueous electrolyte appropriate viscosity and ionic conductivity, which is advantageous for lithium ion transport and improving the rate performance of secondary batteries. Although carboxylate compounds can improve the output performance of secondary batteries, their antioxidant capacity is low and they are prone to decomposition when stored in a highly charged state, so their content should not be too high. In some embodiments, the mass content of the carboxylate compound is B3 (%) relative to the total mass of the non-aqueous electrolyte, and B3 is 0 to 15. In some embodiments, B3 may be 0. In some embodiments, B3 is selectively 2 to 15, 2 to 10, 2 to 8, or 2 to 5.

[0105] The organic solvent of this application may include solvents other than the cyclic carbonate compounds, linear carbonate compounds, and carboxylate compounds described above. For example, the other solvent may include sulfone solvents such as sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0106] In some embodiments, the content A1(%) of the compound represented by Formula 1 and the content B1(%) of the cyclic carbonate compound satisfy the condition that B1 / 20 + A1 is between 1 and 3, and selectively range from 1 to 2, 1 to 1.8, 1 to 1.6, and 1 to 1.4. By appropriately combining the content A1(%) of the compound represented by Formula 1 and the content B1(%) of the cyclic carbonate compound, it is possible to improve the capacity retention rate of the secondary battery while mitigating problems such as degradation of output performance and increased safety risks due to the thinning of the current collector. Furthermore, the following situation can be effectively avoided: When the content of both the compound represented by Formula 1 and the cyclic carbonate compound is high, the internal resistance and gas generation of the battery are high, which may affect the output performance and storage performance of the secondary battery. If the content of both the compound represented by Formula 1 and the cyclic carbonate compound is low, the ionic conductivity of the non-aqueous electrolyte will be low, and the compound represented by Formula 1, which forms low-resistance positive and negative electrode interface films and a passivation film on the surface of the positive electrode current collector, will be insufficient. This may result in a deterioration of the output performance, safety performance, and cycle performance of the secondary battery. [Additives]

[0107] In some embodiments, the non-aqueous electrolyte may contain additives comprising at least one of the following: halogen-substituted cyclic carbonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, isocyanate compounds, anhydride compounds, sulfate ester compounds, sulfite ester compounds, sulfonic acid ester compounds, and disulfonic acid ester compounds. The types of these additives are not particularly limited in this application, as long as they do not impair the spirit of this application. Selectively, the total mass content of these additives is 5% or less, and more selectively, 2.5% or less, relative to the total mass of the non-aqueous electrolyte.

[0108] Optionally, in some embodiments, the non-aqueous electrolyte may further contain fluoroethylene carbonate (FEC). Its mass content is C1 (%) with respect to the total mass of the non-aqueous electrolyte, and 0 ≦ C1 ≦ 2.5. For example, C1 may be in the range of 0, 0.10, 0.20, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, 2.25, 2.50, or any value within this range. Optionally, 0 < C1 ≦ 2.5, 0 < C1 ≦ 2.25, 0 < C1 ≦ 2.0, 0 < C1 ≦ 1.75, 0 < C1 ≦ 1.5, 0 < C1 ≦ 1.25, 0 < C1 ≦ 1.0, 0 < C1 ≦ 0.75, or 0 < C1 ≦ 0.5.

[0109] In a secondary battery, fluoroethylene carbonate undergoes a reduction decomposition reaction at a high potential, forms an interfacial film with certain flexibility on the surface of the negative electrode active material, and can also suppress the reduction decomposition of the organic solvent at a low potential and the occlusion of the organic solvent into the negative electrode active material. Therefore, when the non-aqueous electrolyte contains fluoroethylene carbonate, the cycle performance of the secondary battery can be effectively improved. Furthermore, fluoroethylene carbonate has strong resistance to high-voltage oxidation and is advantageous for use in combination with a high-voltage negative electrode active material, which is also advantageous for further increasing the energy density of the secondary battery.

[0110] In some embodiments, the content A1 (%) of the compound represented by Formula 1 and the content C1 (%) of fluoroethylene carbonate further satisfy 0.25 ≦ C1 / A1 ≦ 25. Optionally, 0.5 ≦ C1 / A1 ≦ 15, 0.5 ≦ C1 / A1 ≦ 10, 0.5 ≦ C1 / A1 ≦ 5, 0.5 ≦ C1 / A1 ≦ 4, 0.5 ≦ C1 / A1 ≦ 3, 0.5 ≦ C1 / A1 ≦ 一2.5, 0.5 ≦ C1 / A1 ≦ 2, 0.5 ≦ C1 / A1 ≦ 1.5, or 0.5 ≦ C1 / A1 ≦ 1.0.

[0111] When a non-aqueous electrolyte contains fluoroethylene carbonate, the cycle performance of a secondary battery can be effectively improved. However, fluoroethylene carbonate tends to decompose and form HF, which corrodes the positive electrode active material, increasing the heat and gas generation of the secondary battery. On the other hand, the compound represented by Formula 1 can function as a stabilizer for the positive electrode active material. The B atoms in its structure have the function of interacting with the O atoms on the surface of the positive electrode active material, thereby stabilizing the crystal structure of the positive electrode active material and reducing the damage that HF ​​inflicts on the crystal structure of the positive electrode active material. Therefore, using the compound represented by Formula 1 in combination with fluoroethylene carbonate is advantageous in fully demonstrating the effect of fluoroethylene carbonate in further improving the cycle performance of secondary batteries. Furthermore, by appropriately controlling the relationship between the content A1 (%) of the compound represented by Equation 1 and the content C1 (%) of fluoroethylene carbonate to satisfy 0.25 ≤ C1 / A1 ≤ 25, the synergistic effect between the compound represented by Equation 1 and fluoroethylene carbonate can be fully exerted, contributing to further improvement of the cycle performance of the secondary battery while mitigating problems such as degradation of output performance and increased safety risks due to the thinning of the current collector. In addition, because fluoroethylene carbonate has a high dielectric constant, by appropriately controlling the relationship between the content A1 (%) of the compound represented by Equation 1 and the content C1 (%) of fluoroethylene carbonate to satisfy 0.25 ≤ C1 / A1 ≤ 25, the cations and anions of the compound represented by Equation 1 form free ions, ensuring a reduction in cation and anion bonding. This improves the ionic conductivity of the non-aqueous electrolyte, improving the cycle performance of the secondary battery while increasing the number of active lithium ions.

[0112] In some embodiments, the non-aqueous electrolyte may further contain a dehydrating additive. The dehydrating additive reduces the water content of the non-aqueous electrolyte, thereby reducing a series of side reactions caused by moisture, which can reduce the amount of gas and heat generated in the secondary battery and improve the storage and safety performance of the secondary battery. Selectively, in some embodiments, the dehydrating additive includes hexamethyldisilazane (HMDS), tris(trimethylsilyl) phosphate (TMSP), or a combination thereof. In addition to effectively reducing the water content of the non-aqueous electrolyte, these two dehydrating additives can react with lithium hexafluorophosphate to form lithium difluorophosphate. This reduces the decomposition of lithium hexafluorophosphate and the formation of HF, while further stabilizing the positive electrode interface film and / or negative electrode interface film, reducing the resistance of the positive electrode interface and / or negative electrode interface, and contributing to further improvements in the output performance, storage performance, and safety performance of the secondary battery.

[0113] In some embodiments, the mass content of the dehydrating additive is 2% or less, selectively 0.05% to 1%, and more selectively 0.1% to 1%, relative to the total mass of the non-aqueous electrolyte.

[0114] The non-aqueous electrolyte of the present invention can be manufactured by conventional methods in the art. For example, the non-aqueous electrolyte can be obtained by uniformly mixing the organic solvent, the lithium salt, the additive, etc. The order in which the materials are added is not particularly limited; for example, the non-aqueous electrolyte can be obtained by adding the lithium salt and the additive, etc., to the organic solvent and mixing them uniformly.

[0115] In this application, each component in the non-aqueous electrolyte and their content can be measured by methods known in the art. For example, they can be measured by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), NMR spectroscopy (NMR), etc.

[0116] Furthermore, when testing the non-aqueous electrolyte of this application, it is possible to obtain the non-aqueous electrolyte from a secondary battery. One example of a method for obtaining the non-aqueous electrolyte from a secondary battery is to discharge the secondary battery to its discharge cutoff voltage (generally, to fully discharge the battery for safety reasons), then perform a centrifugation process, and then use an appropriate amount of liquid obtained from the centrifugation process as the non-aqueous electrolyte. Alternatively, the non-aqueous electrolyte may be obtained directly from the filling port of the secondary battery.

[0117] In this application, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material may be a negative electrode active material known in the art for secondary batteries. For example, the negative electrode active material includes, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may include at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy material. This application is not limited to these materials, and other conventionally known materials usable as negative electrode active materials for secondary batteries may be used. These negative electrode active materials may be used individually or in combination of two or more.

[0118] In some embodiments, the negative electrode active material layer may optionally further contain a negative electrode conductive agent. The present application does not particularly limit the type of negative electrode conductive agent, and as an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the negative electrode conductive agent is 5% or less of the total mass of the negative electrode active material layer.

[0119] In some embodiments, the negative electrode active material layer may optionally further contain a negative electrode binder. The present application does not particularly limit the type of negative electrode binder. As an example, the negative electrode binder may contain at least one of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous acrylic acid resin (e.g., polyacrylate PAA, polymethacrylate PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass content of the negative electrode binder is 5% or less of the total mass of the negative electrode active material layer.

[0120] In some embodiments, the negative electrode active material layer may selectively further contain other additives. For example, the other additives may include thickeners such as sodium carboxymethylcellulose (CMC-Na), PTC thermistor materials, and so on. In some embodiments, the mass content of the other additives is 2% or less of the total mass of the negative electrode active material layer.

[0121] The negative electrode active material layer is typically obtained by coating a negative electrode slurry onto a negative electrode current collector, drying it, and cold-pressing it. The negative electrode slurry is typically obtained by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and any other optional auxiliary agents in a solvent and stirring it uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0122] In this application, the positive electrode active material layer includes a positive electrode active material. As the positive electrode active material, a positive electrode active material for secondary batteries known in the art may be used. For example, the positive electrode active material may include at least one of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modifiers. Examples of lithium transition metal oxides may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modifiers. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate-carbon composites, lithium manganese phosphate, lithium manganese phosphate-carbon composites, lithium iron manganese phosphate, lithium iron manganese phosphate-carbon composites, and their respective modifiers. This application is not limited to these materials, and other conventionally known materials usable as positive electrode active materials for secondary batteries may be used. These positive electrode active materials may be used individually or in combination of two or more.

[0123] In some embodiments, the positive electrode active material has the molecular formula Li a Ni b Co c Mn d Al e M f O g A h The material contains a layered structure where M represents a transition metal site-doped cation and A represents an oxygen site-doped anion, with 0.8 ≤ a ≤ 1.2, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, 0 ≤ e ≤ 1, 0 ≤ f ≤ 0.2, 0 ≤ g ≤ 2, 0 ≤ h ≤ 2, b + c + d + e + f = 1, and g + h = 2.

[0124] The molecular formula is Li a Ni b Co c Mn d Al e M f Og A h The layered material can be selectively modified by M cation doping, A anion doping, or both M cation and A anion doping. The layered material obtained by doping has a more stable crystal structure, less lattice oxygen deposition, and less desorption of transition metal ions. This reduces a series of side reactions and improves the safety performance, cycle performance, dynamic characteristics, and other electrochemical properties of the secondary battery.

[0125] In some embodiments, M is at least one selected from Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W.

[0126] In some embodiments, A is at least one selected from F, N, P, and S. Selectively, A is selected from F. By doping and modifying with F, Li a Ni b Co c Mn d Al e M f O g A h This results in a more stable crystal structure, making it less likely for lattice oxygen to precipitate and less likely for transition metal ions to be desorbed. As a result, secondary batteries have superior safety performance, cycle performance, and dynamic characteristics.

[0127] The values ​​of a, b, c, d, e, f, g, h are Li a Ni b Co c Mn d Al e M f O g A h It satisfies the requirement of keeping it electrically neutral.

[0128] In some embodiments, 0 < b < 0.98. Optionally, 0.50 ≤ b < 0.98, 0.55 ≤ b < 0.98, 0.60 ≤ b < 0.98, 0.65 ≤ b < 0.98, 0.70 ≤ b < 0.98, 0.75 ≤ b < 0.98, or 0.80 ≤ b < 0.98.

[0129] In some embodiments, c = 0.

[0130] In some embodiments, 0 < c ≤ 0.20. Optionally, 0 < c ≤ 0.15, 0 < c ≤ 0.10, 0 < c ≤ 0.09, 0 < c ≤ 0.08, 0 < c ≤ 0.07, 0 < c ≤ 0.06, 0 < c ≤ 0.05, 0 < c ≤ 0.04, 0 < c ≤ 0.03, 0 < c ≤ 0.02, or 0 < c ≤ 0.01. Cobalt has a low content in the earth's crust, is difficult to mine, and has a high price. Therefore, low cobalt or cobalt-free is an inevitable development trend of the positive electrode active material. However, cobalt greatly contributes to the lithium ion diffusion rate of the positive electrode active material. Low cobalt or cobalt-free reduces the lithium ion diffusion rate of the positive electrode active material and affects the cycle performance of the secondary battery. Researchers are paying attention to improving the lithium ion diffusion rate of low cobalt or cobalt-free positive electrode active materials, but there is no good solution yet.

[0131] As a surprising discovery made by the inventors of the present application, the B atom in the compound structure represented by Formula 1 is likely to bind to the O atom in the cathode active material, reducing the charge transfer resistance of the cathode active material, and thus reducing the diffusion resistance of lithium ions within the cathode active material bulk. Therefore, a low-cobalt or cobalt-free cathode active material can significantly improve the diffusion rate of lithium ions. Lithium ions within the low-cobalt or cobalt-free cathode active material bulk are timely replenished on the surface, avoiding excessive lithium desorption on the surface of the low-cobalt or cobalt-free cathode active material, and stabilizing the crystal structure of the low-cobalt or cobalt-free cathode active material. Since the crystal structure of the low-cobalt or cobalt-free cathode active material of the present application becomes more stable, problems such as instability of the structural, chemical or electrochemical properties of the cathode active material due to excessive lithium desorption on the surface of the low-cobalt or cobalt-free cathode active material are reduced, for example, the probability of occurrence of irreversible distortion or an increase in lattice defects of the cathode active material is reduced.

[0132] In some embodiments, d = 0 and 0 < e < 0.50. Optionally, d = 0 and 0 < e ≤ 0.45, d = 0 and 0 < e ≤ 0.40, d = 0 and 0 < e ≤ 0.35, d = 0 and 0 < e ≤ 0.30, d = 0 and 0 < e ≤ 0.25, d = 0 and 0 < e ≤ 0.20, d = 0 and 0 < e ≤ 0.15, or d = 0 and 0 < e ≤ 0.10.

[0133] In some embodiments, e = 0 and 0 < d < 0.50. Optionally, e = 0 and 0 < d ≤ 0.45, e = 0 and 0 < d ≤ 0.40, e = 0 and 0 < d ≤ 0.35, e = 0 and 0 < d ≤ 0.30, e = 0 and 0 < d ≤ 0.25, e = 0 and 0 < d ≤ 0.20, e = 0 and 0 < d ≤ 0.15, or e = 0 and 0 < d ≤ 0.10.

[0134] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Optionally, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0135] In some embodiments, g = 2 and h = 0.

[0136] In some examples, g=0 and h=2.

[0137] In some embodiments, 0 <g<2、0<h<2、かつ、g+h=2である。

[0138] For example, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The layered material is LiNi 0.7 Mn 0.3 O2, LiLiLi 0.69 Co 0.01 Mn 0.3 O2, LiLiLi 0.68 Co 0.02 Mn 0.3 O2, LiLiLi 0.65 Co 0.05 Mn 0.3 O2, LiLiLi 0.63 Co 0.07 Mn 0.3 O2, LiLiLi 0.61 Co 0.09 Mn 0.3 It contains, but is not limited to, at least one of the O2 species.

[0139] Li a Ni b Co c Mn d Al e M f O g A h It can be manufactured by conventional methods in the art. As an example of a manufacturing method, it can be obtained by mixing a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M element precursor, and an A element precursor and sintering them. The sintering atmosphere may be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen gas atmosphere. The O2 concentration of the sintering atmosphere is, for example, 70% to 100%. The sintering temperature and sintering time can be adjusted according to the actual conditions.

[0140] As an example, the lithium source includes, but is not limited to, at least one of lithium oxide (Li2O), lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), lithium acetate (CH3COOLi), lithium hydroxide (LiOH), lithium carbonate (Li2CO3), and lithium nitrate (LiNO3). As an example, the nickel source includes, but is not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As an example, the cobalt source includes, but is not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As an example, the manganese source includes, but is not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As an example, the aluminum source includes, but is not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As an example, the precursor of element M includes, but is not limited to, at least one of the oxide, nitrate compound, carbonate compound, hydroxide compound, and acetate compound of element M. As an example, the precursor of element A includes, but is not limited to, at least one of ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid, ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium hydrosulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0141] In some embodiments, the content of the layered material having the molecular formula Li a Ni b Co c Mn d Al e M f O g A h is 80% to 99% based on the total mass of the positive electrode active material layer. For example, the molecular formula is Lia Ni b Co c Mn d Al e M f O g A h The content of the layered material being as such may be in a range consisting of any value of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or more. Optionally, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The content of the layered material being as such is 85% - 99%, 90% - 99%, 95% - 99%, 80% - 98%, 85% - 98%, 90% - 98%, 95% - 98%, 80% - 97%, 85% - 97%, 90% - 97%, or 95% - 97%.

[0142] In some embodiments, the positive electrode active material layer may optionally further contain a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. In some embodiments, based on the total mass of the positive electrode active material layer, the mass content of the positive electrode conductive agent is 5% or less.

[0143] In some embodiments, the positive electrode active material layer may optionally further contain a positive electrode binder. The present application does not particularly limit the type of the positive electrode binder. For example, the positive electrode binder may contain at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a ternary copolymer of vinylidene fluoride-tetrafluoroethylene-propylene, a ternary copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, or a fluorine-containing acrylate resin. In some embodiments, the mass content of the positive electrode binder is 5% or less of the total mass of the positive electrode active material layer.

[0144] The positive electrode active material layer is typically obtained by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold-pressing it. The positive electrode slurry is typically obtained by dispersing the positive electrode active material, a selective conductive agent, a selective binder, and any other components in a solvent and stirring them uniformly. The solvent may, but is not limited to, N-methylpyrrolidone (NMP).

[0145] In this application, the separator is provided between the positive electrode sheet and the negative electrode sheet, and primarily serves to prevent short circuits between the positive and negative electrodes, while also allowing lithium ions to pass through. This application does not particularly limit the type of separator, and any known porous separator having excellent chemical and mechanical stability may be used.

[0146] In some embodiments, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multilayer composite thin film. If the separator is a multilayer composite thin film, the materials of each layer may be the same or different.

[0147] In some embodiments, the casing of the secondary battery may be a hard case such as a hard plastic case, an aluminum case, or a steel case. The casing of the secondary battery may also be a soft bag such as a bag-type soft bag. The material of the soft bag may be a plastic such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), or polybutylene succinate (PBS).

[0148] This invention does not particularly limit the shape of the secondary battery, and it may be cylindrical, rectangular, or any other shape. Figure 1 shows an example of a secondary battery 5 with a rectangular structure.

[0149] In some embodiments, as shown in Figure 2, the exterior may include a case 51 and a cover plate 53. The case 51 may include a bottom plate and side plates connected to the bottom plate, with the bottom plate and side plates defining a storage chamber. The case 51 has an opening communicating with the storage chamber, and the cover plate 53 covers the opening to seal the storage chamber. A positive electrode sheet, a negative electrode sheet, and a separator may be formed into an electrode assembly 52 by a winding or lamination process. The electrode assembly 52 is sealed in the storage chamber. A non-aqueous electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and may be adjusted as required.

[0150] The method for manufacturing the secondary battery of the present invention is known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and a non-aqueous electrolyte can be assembled to form a secondary battery. For example, the positive electrode sheet, separator, and negative electrode sheet can be assembled into an electrode assembly by a winding process or a lamination process, the electrode assembly can be placed in an outer casing, dried, and then a non-aqueous electrolyte can be injected. The secondary battery can then be obtained through processes such as vacuum sealing, standing, chemical formation, and shaping.

[0151] In some embodiments of the present invention, the secondary battery according to the present invention may be incorporated as a battery module. The battery module may contain multiple secondary batteries, and the specific number can be adjusted according to the use and capacity of the battery module.

[0152] Figure 3 is a schematic diagram of an example of a battery module 4. As shown in Figure 3, in the battery module 4, the multiple secondary batteries 5 may be arranged sequentially along the longitudinal direction of the battery module 4. Of course, they may be arranged in other configurations. Also, these multiple secondary batteries 5 may be fixed together with fasteners.

[0153] Optionally, the battery module 4 may have a housing with storage space, and multiple secondary batteries 5 are housed in this storage space.

[0154] In some embodiments, the above-described battery modules may be assembled as a battery pack. The number of battery modules included in the battery pack can be adjusted according to the usage and capacity of the battery pack.

[0155] Figures 4 and 5 are schematic diagrams of an example of a battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided inside the battery box. The battery box may include an upper box 2 and a lower box 3. The upper box 2 covers the lower box 3, forming a sealed space for housing the battery modules 4. The plurality of battery modules 4 may be arranged inside the battery box in any configuration.

[0156] Embodiments of the present invention further provide a power consumption device comprising at least one of the secondary battery, battery module, or battery pack of the present invention. The secondary battery, battery module, or battery pack can be used as a power source for the power consumption device or as an energy storage unit for the power consumption device. The power consumption device may be, 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.), trains, ships and satellites, energy storage systems, etc.

[0157] The aforementioned power consumption device may be configured to use a secondary battery, battery module, or battery pack, depending on the requirements of its use.

[0158] Figure 6 is a schematic diagram of an example of a power consumption device. This power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. Battery packs or battery modules can be used to meet the high power and high energy density requirements of this power consumption device.

[0159] Other examples of power-consuming devices include mobile phones, tablet computers, and laptop computers. Since these power-consuming devices are usually required to be lightweight and thin, they can use rechargeable batteries as a power source. Examples

[0160] The following examples are provided for illustrative purposes only, as they illustrate the contents disclosed herein and it will be obvious to those skilled in the art that various modifications and changes can be made within the scope of the contents disclosed herein. Unless otherwise specified, all parts, percentages, and ratios reported in the following examples are based on mass. All reagents used in the examples are commercially available or can be synthesized by conventional methods and can be used directly without further processing. The equipment used in the examples is also commercially available.

[0161] The secondary batteries of Examples 1-30 and Comparative Examples 1-4 are all manufactured by the following method. Manufacturing of positive electrode sheets

[0162] LiNi 0.65 Co 0.05 Mn 0.3 O2, carbon black (Super P) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were thoroughly mixed with an appropriate amount of solvent NMP in a mass ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry was uniformly coated onto the surface of aluminum foil, which served as the positive electrode current collector, dried, and cold-pressed to obtain a positive electrode sheet. The thickness H2 (μm) of the positive electrode current collector, the elongation at break Q (%), and the compressive density P2 (g / cm³) of the positive electrode active material layer were determined. 3 The specific ranges of each are shown in Table 1. Manufacturing of negative electrode sheets

[0163] A uniform negative electrode slurry was formed by thoroughly mixing graphite (negative electrode active material), styrene-butadiene rubber (SBR) (binder), sodium carboxymethylcellulose (CMC-Na) (thickener), and carbon black (Super P) (conductive agent) in a mass ratio of 96.2:1.8:1.2:0.8 with an appropriate amount of deionized water (solvent) to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the copper foil of the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode sheet. The thickness H1 (μm) of the negative electrode current collector and the compressed density P1 (g / cm³) of the negative electrode active material layer were determined. 3 The specific ranges of each are shown in Table 1. Separator

[0164] A porous polyethylene (PE) membrane was used as a separator. Manufacturing of non-aqueous electrolytes

[0165] A cyclic carbonate compound, a linear carbonate compound, and a carboxylate compound were uniformly mixed to obtain an organic solvent with the composition shown in Table 1. Then, the compound represented by Formula 1, fluoroethylene carbonate (FEC), lithium hexafluorophosphate (LiPF6), and lithium bisfluorosulfonylimide (LiFSI) were added to the organic solvent and uniformly mixed to obtain a non-aqueous electrolyte with the composition shown in Table 1. In Table 1, the content of each component is based on the total mass of the non-aqueous electrolyte, and " / " means that the corresponding component was not added. Manufacturing of rechargeable batteries

[0166] A positive electrode sheet, a separator, and a negative electrode sheet were sequentially laminated and wound to obtain an electrode assembly. The electrode assembly was placed in an outer casing, dried, a non-aqueous electrolyte was injected, and after processes such as vacuum sealing, standing, chemical formation, and shaping, a secondary battery was obtained. Test section (1) Test of the mass energy density of secondary batteries

[0167] At 25°C, the secondary battery was charged to 4.25V with a constant current of 0.33C, and then further charged with a constant voltage until the current reached 0.05C. After the secondary battery was left standing for 5 minutes, it was discharged to 2.8V with a constant current of 0.33C to obtain the discharge energy. The mass energy density of the secondary battery (Wh / Kg) = discharge energy / mass of the secondary battery. (2) Testing of the output performance of secondary batteries

[0168] At 25°C, the secondary battery was charged to 4.25V with a constant current of 0.1C, and then further charged with a constant voltage until the current became 0.05C, at which point the secondary battery was fully charged. The secondary battery was discharged with a constant current of 1C for approximately 30 minutes to adjust its charge state to 50% SOC, at which point the voltage of the secondary battery was defined as V0. The secondary battery was discharged with a current of 4C I1 for 30 seconds, with the voltage scored every 0.1 seconds, and the voltage at the end of discharge was defined as V1. The internal resistance of the secondary battery is DCR = (V0 - V1) / I1. The smaller the internal resistance of the secondary battery, the better its output performance. (3) Testing of the safety performance of secondary batteries in a hot box

[0169] At 25°C, the secondary battery was charged to 4.25V with a constant current of 0.1C, and then further charged with a constant voltage until the current reached 0.05C, at which point the secondary battery was fully charged. The fully charged secondary battery was placed in a highly sealed high-temperature box and heated to 100°C at a rate of 5°C / min, held for 1 hour, then heated to 105°C at a rate of 5°C / min and held for 30 minutes. Subsequently, the temperature was increased at a rate of 5°C / min, with 30 minutes of heating for every 5°C increase until the secondary battery became unusable, until the maximum temperature T before the secondary battery became unusable was reached. max It recorded. T max The higher the value, the better the hot box safety performance of the secondary battery. (4) Testing of the cycle performance of secondary batteries

[0170] At 45°C, the secondary battery was charged to 4.25V with a constant current of 1C, and then further charged with a constant voltage until the current became 0.05C, at which point the secondary battery was fully charged. The charge capacity at this time was recorded and defined as the charge capacity for the first cycle. After the secondary battery was left to stand for 5 minutes, it was discharged to 2.8V with a constant current of 1C, which was defined as one charge-discharge cycle, and the discharge capacity at this time was recorded and defined as the discharge capacity for one cycle. The secondary battery was subjected to repeated charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded. The capacity retention rate (%) of the secondary battery after 600 cycles at 45°C = Discharge capacity after 600 cycles / Discharge capacity per cycle × 100%. (5) Testing of the storage performance of secondary batteries

[0171] At 60°C, a secondary battery was charged to 4.25V with a constant current of 1C, and then further charged with a constant voltage until the current reached 0.05C. At this time, the volume of the secondary battery was tested by the drainage method and defined as V0. The secondary battery was placed in a constant temperature chamber at 60°C and stored for 30 days. After being removed, the volume of the secondary battery was tested by the drainage method and defined as V1. The volume expansion rate (%) of the secondary battery after 30 days of storage at 60°C is [(V1-V0) / V0].

[0172] Table 1 shows the manufacturing parameters for the positive electrode sheet, negative electrode sheet, and non-aqueous electrolyte of Examples 1-30 and Comparative Examples 1-4. Table 2 shows the results of testing Examples 1-30 and Comparative Examples 1-4 using the performance test method described above.

[0173] [Table 1]

[0174] [Table 2]

[0175] As can be seen from the test results in Tables 1 and 2, in secondary batteries using a thinned negative electrode current collector, the non-aqueous electrolyte contains the compound represented by formula 1, and its content A1 (%), the thickness H1 (μm) of the negative electrode current collector, and the compressed density P1 (g / cm³) of the negative electrode active material layer are all related. 3 If the conditions are met such that A1 / H1 is 0.003 to 0.40 and P1 / A1 is 1 to 90, the secondary battery can possess high energy density, low internal resistance, high hot-box safety performance, high capacity retention rate, and low volume expansion rate.

[0176] As can be seen from the test results of Examples 1-9 and Comparative Example 2, when A1 / H1 is less than 0.003 and / or P1 / A1 is greater than 90, the compound represented by Formula 1 that forms a low-resistance negative electrode interface film is insufficient. As a result, the resistance of the negative electrode interface is high, and the deterioration of the battery's internal resistance and heat generation due to thinning the negative electrode current collector cannot be effectively reduced. Consequently, the output performance and safety performance of the secondary battery deteriorate, and the increase in the capacity retention rate of the secondary battery is limited.

[0177] As can be seen from the test results of Examples 1-9 and Comparative Examples 3-4, when A1 / H1 is greater than 0.40 and / or P1 / A1 is less than 1, there is too much of the compound represented by Formula 1, and the resistance at the negative electrode interface does not decrease, but rather increases. This results in high internal resistance of the secondary battery and poor capacity retention. The compound represented by Formula 1 provides some of the active lithium ions and can slightly improve the energy density of the secondary battery, but the decomposition of anions increases the amount of gas generated inside the battery, which clearly degrades the hot box safety performance.

[0178] As can be seen from the test results in Tables 1 and 2, when a thinned positive electrode current collector is also used in a secondary battery, the compound content A1 (%) represented by Equation 1, the thickness H2 (μm) of the positive electrode current collector, the elongation at break Q (%) of the positive electrode current collector, and the compressed density P2 (g / cm³) of the positive electrode active material layer are all related. 3 When the following conditions are met, A1 / H2 is 0.0015-0.20, Q+A1 is 1-4, and P2 / A1 is 2-340, the secondary battery has low internal resistance, high hot-box safety performance, high capacity retention rate, and low volume expansion rate, while also having improved energy density. Possible reasons for this include the fact that the compound represented by formula 1 is preferentially oxidized on the surface of the positive electrode active material over organic solvents, and its oxidation products have low resistance properties, which is advantageous for forming a low-resistance positive electrode interface film. In addition, the B atoms in the molecular structure of the compound represented by formula 1 readily bond strongly with inorganic components such as LiF in the positive electrode interface film, thus accelerating lithium ion transport and significantly reducing the battery's internal resistance and heat generation.

[0179] Furthermore, this application is not limited to the embodiments described above. The embodiments described above are merely examples, and any embodiment that has substantially the same configuration as the technical concept and exhibits the same effects within the scope of the technical proposal of this application is included within the scope of this application. In addition, other forms that are constructed by adding various modifications to the embodiments that a person skilled in the art could conceive of, and by combining some of the components of the embodiments, are also included within the scope of this application, as long as they do not depart from the spirit of this application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte, The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The non-aqueous electrolyte contains a compound represented by formula 1, The mass percentage of the compound represented by formula 1 is A1 (%) relative to the total mass of the non-aqueous electrolyte, the thickness of the negative electrode current collector is H1 (μm), and the compressed density of the negative electrode active material layer is P1 (g / cm³). ３ ) and the secondary battery has H1 of 3 to 7, A1 of 0.02 to 1.6, and P1 of 1.4 to 1.

8. The non-aqueous electrolyte further comprises a first lithium salt containing a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, The mass percentage of lithium hexafluorophosphate is A2 (%) relative to the total mass of the non-aqueous electrolyte, and the mass percentage of lithium bisfluorosulfonylimide is A3 (%) relative to the total mass of the non-aqueous electrolyte. A secondary battery that satisfies the following conditions: A2 is between 6 and 14, and A3 is greater than 0 and less than or equal to 4.

3. 【Chemistry 1】 (X and Y each independently represent a fluorine atom, or at least one of the group consisting of partially fluorinated or fully fluorinated C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, and C6-C8 aryloxy, and at least one of X and Y represents a fluorine atom.)

2. A1 / H1 is 0.003 to 0.4 and / or The secondary battery according to claim 1, wherein P1 / A1 is 1 to 90.

3. The thickness of the positive electrode current collector is H2 (μm), the elongation at break of the positive electrode current collector is Q (%), and the compressive density of the positive electrode active material layer is P2 (g / cm³). ３ The secondary battery according to claim 1 or 2, wherein the secondary battery satisfies the following conditions: H2 is 4 to 14, A1 / H2 is 0.0015 to 0.20, Q+A1 is 1 to 4, and P2 / A1 is 2 to 340.

4. A1 / H2 is 0.002 to 0.05 and / or Q+A1 is 1.5 to 3.5, and / or The secondary battery according to claim 3, wherein P2 / A1 is 5 to 340.

5. A1 is 0.05 to 1.5 and / or P1 is 1.55 to 1.75, and / or P2 is 3.2 to 3.7, and / or The secondary battery according to claim 1 or 2, wherein Q is 0.5 to 3.

5.

6. The secondary battery according to claim 1 or 2, wherein A2 / A1 is 5 to 650.

7. A3 / A2 is 0.8 or less, and / or The secondary battery according to claim 1 or 2, wherein A2 / A1 is 5 to 650.

8. The secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte further comprises a second lithium salt containing at least one of lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

9. The secondary battery according to claim 8, wherein the second lithium salt comprises lithium difluorophosphate.

10. The secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte further comprises a cyclic carbonate compound.

11. The secondary battery according to claim 10, wherein the cyclic carbonate compound comprises at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, and vinylethylene carbonate.

12. The secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte further comprises fluoroethylene carbonate.

13. The secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte further comprises a dehydrating additive containing at least one of hexamethyldisilazane and tris(trimethylsilyl)phosphate.

14. The secondary battery according to claim 1, wherein X and Y satisfy one of the following conditions (1) to (3). (1) Both X and Y represent fluorine atoms. (2) Of X and Y, one represents a fluorine atom, and the other represents at least one from the group consisting of partially fluorinated or fully fluorinated C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, phenyl, phenoxy, C1-C5 alkoxy, C2-C5 alkenyloxy, and C2-C5 alkynyloxy. (3) Of X and Y, one represents a fluorine atom, and the other represents at least one of the group consisting of partially fluorinated or fully fluorinated methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadienyl, ethynyl, propynyl, phenyl, methoxy, ethoxy, proxy, vinyloxy, propenyloxy, ethynyloxy, propynyloxy, and phenoxy.

15. The secondary battery according to claim 1, wherein the compound represented by formula 1 comprises at least one of the following compounds. 【Chemistry 2】

16. The negative electrode current collector uses copper foil or copper alloy foil, and / or The secondary battery according to claim 1 or 2, wherein the positive electrode current collector is made of aluminum foil or aluminum alloy foil.

17. A battery module comprising the secondary battery described in claim 1.

18. A battery pack comprising one of the secondary battery described in claim 1 and one of the battery modules described in claim 17.

19. A power consumption device comprising at least one of the secondary battery described in claim 1, the battery module described in claim 17, and the battery pack described in claim 18.

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