Secondary batteries and battery modules, battery packs and electrical devices containing them.

Abstract

A secondary battery (5) and a battery module (4), a battery pack (1), and an electrical device comprising the secondary battery are provided. The secondary battery includes a positive electrode and a non-aqueous electrolyte. The non-aqueous electrolyte includes a compound shown in Formula 1. Based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound shown in Formula 1 is A1%, where A1 is 0.02 to 1.6. The thickness of the positive electrode current collector is H μm, where H is 4 to 14. This allows a secondary battery using a thinned positive electrode current collector to simultaneously achieve low cost, high energy density, high power performance, good processing performance, and high safety performance.

Description

[0001] This application is a divisional application based on the invention with application number 202280012717.0, application date May 23, 2022, applicant CATL, and invention title "Secondary Battery and Battery Module, Battery Pack and Electrical Device Including the Same". Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to a secondary battery and a battery module, battery pack and power-consuming device containing the same. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the increasing application and promotion of rechargeable batteries, the requirements for their energy density are becoming increasingly stringent. Aluminum foil current collectors do not contribute to the capacity of rechargeable batteries. Thinning the aluminum foil current collector can not only reduce costs but also allow for more active material to be accommodated within the limited battery casing. Therefore, thinning the aluminum foil current collector is one of the most effective measures to improve the energy density of rechargeable batteries. Although thinning the aluminum foil current collector can reduce costs and improve the energy density of rechargeable batteries, this approach is difficult to apply in practice, mainly because thinning the aluminum foil current collector increases the battery's internal resistance and heat generation, while also deteriorating the processing performance of the positive electrode and making it prone to breakage. Therefore, currently, rechargeable batteries cannot simultaneously possess low cost, high energy density, high power performance, good processing performance, and high safety performance. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and a battery module, battery pack and power device containing the same, which aims to enable the secondary battery using a thinned positive electrode current collector to simultaneously achieve low cost, high energy density, high power performance, good processing performance and high safety performance.

[0005] A first aspect of this application provides a secondary battery, including a positive electrode and a non-aqueous electrolyte. The positive electrode includes a positive current collector and a positive active material layer located on at least one surface of the positive current collector. The non-aqueous electrolyte includes a compound of Formula 1, where X and Y each independently represent a fluorine atom, or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, C6-C8 aryloxy, and at least one of X and Y represents a fluorine atom.

[0006]

[0007] Based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound shown in Formula 1 is A1%, where A1 is 0.02 to 1.6; the thickness of the positive electrode current collector is H μm, where H is 4 to 14.

[0008] In any embodiment of this application, when the content of the compound shown in Formula 1 is within a suitable range, a passivation film with a suitable thickness can be formed on the surface of the positive electrode current collector, while a low-resistance interface film is formed on the surface of the positive electrode active material, thereby improving the defects such as deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector.

[0009] In any embodiment of this application, A1 is 0.05 to 0.8. This can mitigate the defects caused by thinning of the positive current collector, such as deterioration in power performance, increased safety hazards, and deterioration in processing performance.

[0010] In any embodiment of this application, H is 9 to 14.

[0011] In any embodiment of this application, A1 / H is 0.0017 to 0.20, optionally 0.005 to 0.15, and more preferably 0.005 to 0.1. This helps to improve the strength of the positive electrode current collector, improve the processing performance of the positive electrode sheet, and reduce or even avoid the occurrence of strip breakage; at the same time, it helps the secondary battery to have high power performance and high safety performance.

[0012] In any embodiment of this application, the compaction density of the positive electrode active material layer is P g / cm³. 3 P is 3.2 to 3.7, optionally 3.4 to 3.7. This helps to improve the energy density of the secondary battery.

[0013] In any embodiment of this application, the compaction density of the positive electrode active material layer is P g / cm³. 3 The P / A1 is 2 to 175, optionally 2 to 100, and more optionally 5 to 75. This helps to improve the power performance and safety performance of the secondary battery.

[0014] In any embodiment of this application, the elongation at break of the positive electrode current collector is Q%, where Q is 0.5 to 3.5, optionally 1.5 to 3.5. This results in the positive electrode current collector having high strength and good processing performance, being less prone to breakage, and contributing to the high safety performance of the secondary battery.

[0015] In any embodiment of this application, the elongation at break of the positive current collector is Q%, and Q+A1 is 1 to 4, optionally 1.5 to 3.5, and more preferably 2.0 to 3.5. This helps to improve the strength of the positive current collector, improve the processing performance of the positive electrode sheet, and reduce or even avoid the occurrence of strip breakage; at the same time, it helps the secondary battery to have high power performance and high safety performance.

[0016] In any embodiment of this application, the compaction density of the positive electrode active material layer is P g / cm³. 3 The elongation at break of the positive current collector is Q%, and the secondary battery satisfies the following conditions: H is 11 to 14, A1 / H is 0.005 to 0.15, Q+A1 is 1 to 4, and P / A1 is 2 to 100. Optionally, A1 / H is 0.005 to 0.1, Q+A1 is 1.5 to 3.5, and P / A1 is 5 to 75.

[0017] In any embodiment of this application, the compaction density of the positive electrode active material layer is P g / cm³. 3 The elongation at break of the positive current collector is Q%, and the secondary battery satisfies the following: H is 4 to 11, A1 / H is 0.006 to 0.1, Q+A1 is 1 to 4, and P / A1 is 2 to 100. Optionally, H is 9 to 11, A1 / H is 0.01 to 0.05, Q+A1 is 1.5 to 3.5, and P / A1 is 5 to 75.

[0018] Optionally, in any embodiment of this application, the non-aqueous electrolyte further includes a first lithium salt, which includes lithium hexafluorophosphate, and the mass percentage of the lithium hexafluorophosphate is A2%, based on the total mass of the non-aqueous electrolyte.

[0019] In any embodiment of this application, A2 / A1 may optionally be 5 to 650, and more preferably 15 to 300. This helps to further improve the capacity retention of the secondary battery while mitigating problems such as deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector.

[0020] In any embodiment of this application, A2 may optionally be 6 to 14.

[0021] In any embodiment of this application, optionally, the non-aqueous electrolyte further includes a first lithium salt, which comprises a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the mass percentage of lithium hexafluorophosphate is A2% and the mass percentage of lithium bis(fluorosulfonyl)imide is A3%, both based on the total mass of the non-aqueous electrolyte. Optionally, A2 is 6 to 14, and A3 is greater than 0 and less than or equal to 5.

[0022] In any embodiment of this application, optionally, A3 / A2 is below 0.8, more preferably from 0.05 to 0.3. This helps to form an interface film with lower impedance. Optionally, A2 / A1 is from 5 to 650, more preferably from 15 to 300. This helps to further improve the capacity retention of the secondary battery while mitigating problems such as deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector.

[0023] In any embodiment of this application, optionally, the non-aqueous electrolyte further includes a second lithium salt, which includes at least one of lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium difluorophosphate, lithium difluorodioxarate phosphate, and lithium tetrafluorooxarate phosphate. The total mass percentage of the second lithium salt in the non-aqueous electrolyte is A4%, based on the total mass of the non-aqueous electrolyte. Optionally, A4 is less than 5, more preferably less than 2. The second lithium salt can serve as an auxiliary lithium salt, further improving the interfacial properties of the positive and / or negative electrodes, or improving the ionic conductivity or thermal stability of the non-aqueous electrolyte.

[0024] In any embodiment of this application, optionally, the second lithium salt comprises lithium difluorophosphate. Optionally, the mass ratio α of the lithium difluorophosphate to the lithium hexafluorophosphate is 0.01 to 0.15, more preferably 0.01 to 0.1. Lithium difluorophosphate has high electrochemical stability, can improve the ionic conductivity of non-aqueous electrolytes, improve the properties of the positive and / or negative electrode interface films, and help construct stable and low-resistance positive and / or negative electrode interface films, thereby effectively reducing the decomposition of non-aqueous electrolytes and further improving the power performance and safety performance of secondary batteries.

[0025] In any embodiment of this application, optionally, the non-aqueous electrolyte further includes a cyclic carbonate compound, the cyclic carbonate compound comprising B1% by mass based on the total mass of the non-aqueous electrolyte. Optionally, B1 is 0.5 to 20, more preferably 15 to 18.

[0026] In any embodiment of this application, B1 / 20+A1 may optionally be 1 to 3, and more preferably 1 to 2. This helps to further improve the capacity retention of the secondary battery while mitigating problems such as deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector.

[0027] In any embodiment of this application, optionally, the cyclic carbonate compound includes at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, and ethylene ethylene carbonate.

[0028] Optionally, in any embodiment of this application, the non-aqueous electrolyte further includes a chain carbonate compound, wherein the chain carbonate compound has a mass percentage of B2, and B2 is 45 to 80, based on the total mass of the non-aqueous electrolyte.

[0029] In any embodiment of this application, optionally, the non-aqueous electrolyte further includes a carboxylic acid ester compound, wherein the mass percentage of the carboxylic acid ester compound is B3%, and B3 is 2 to 15%.

[0030] Optionally, in any embodiment of this application, the non-aqueous electrolyte further includes additives, which include at least one of halogen-substituted cyclic carbonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, isocyanate compounds, acid anhydride compounds, sulfate ester compounds, sulfite ester compounds, sulfonate compounds, and disulfonate compounds, wherein the total mass percentage of the additives is less than 5% based on the total mass of the non-aqueous electrolyte.

[0031] In any embodiment of this application, optionally, the non-aqueous electrolyte further includes fluoroethylene carbonate, with a mass percentage of C1% based on the total mass of the non-aqueous electrolyte. Optionally, 0 < C1 ≤ 2.5, and more preferably, 0 < C1 ≤ 2.0. This effectively improves the cycle performance of the secondary battery.

[0032] In any embodiment of this application, optionally, 0.25 ≤ C1 / A1 ≤ 25, and more preferably, 0.5 ≤ C1 / A1 ≤ 10. This helps to further improve the cycle performance of the secondary battery while mitigating the problems of deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector.

[0033] In any embodiment of this application, optionally, the non-aqueous electrolyte further includes a dehydrating additive, which includes at least one selected from hexamethyldisilazane and tris(trimethylsilyl)phosphate. Optionally, the dehydrating additive has a mass percentage of less than 2%, more preferably 0.05% to 1%, based on the total mass of the non-aqueous electrolyte. This helps to further improve the power performance, storage performance, and safety performance of the secondary battery.

[0034] In any embodiment of this application, optionally, X and Y both represent fluorine atoms.

[0035] In any embodiment of this application, optionally, one of X and Y represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, phenyl, phenoxy, C1-C5 alkoxy, C2-C5 alkenyloxy, and C2-C5 alkynoxy.

[0036] In any embodiment of this application, optionally, one of X and Y represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadienyl, ethynyl, propynyl, phenyl, methoxy, ethoxy, propoxy, ethyleneoxy, propenyloxy, ethynyloxy, propynyloxy, and phenoxy.

[0037] The presence of fluorine atoms helps to form thinner fluorine-containing positive and / or negative electrode interface films, thereby facilitating the uniform transport of lithium ions and effectively suppressing the formation of lithium dendrites.

[0038] In any embodiment of this application, optionally, the compound shown in Formula 1 includes at least one of the following compounds:

[0039]

[0040] Optionally, in any embodiment of this application, the positive current collector is made of aluminum foil or aluminum alloy foil.

[0041] In any embodiment of this application, optionally, the positive electrode active material layer includes a positive electrode active material, which includes at least one of lithium transition metal oxides, lithium phosphates with olivine structures, and their respective modified compounds.

[0042] A second aspect of this application provides a battery module that includes the secondary battery of the first aspect of this application.

[0043] A third aspect of this application provides a battery pack, which includes one of the secondary battery of the first aspect of this application and the battery module of the second aspect.

[0044] The fourth aspect of this application provides an electrical device that includes at least one of the secondary battery of the first aspect of this application, the battery module of the second aspect, and the battery pack of the third aspect.

[0045] The battery module, battery pack, and power device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0046] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0048] Figure 2 yes Figure 1 An exploded view of the implementation method of the secondary battery.

[0049] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0050] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0051] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0052] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0053] The accompanying drawings are not necessarily drawn to scale. The reference numerals are as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the secondary battery, battery module, battery pack, and power-consuming device included herein. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) 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 it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0060] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0061] Throughout this specification, substituents of compounds are disclosed by groups or ranges. It is expressly intended that such description include each individual sub-combination of members of these groups and ranges. For example, it is expressly intended that the term "C1-C6 alkyl" individually discloses alkyl groups 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.

[0062] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0063] In this application, the thickness of the current collector and the active material layer has a meaning known in the art and can be tested using methods known in the art. For example, it can be measured using a micrometer.

[0064] In this application, the compaction density of the active material layer has a meaning known in the art and can be tested using methods known in the art. The compaction density of the active material layer = the areal density of the active material layer / the thickness of the active material layer. The areal density of the active material layer has a meaning known in the art and can be tested using methods known in the art. For example, take an electrode sheet coated on one side and cold-pressed (if it is a double-sided coated electrode sheet, the active material layer on one side can be wiped off first), punch it into a small circular piece with an area of ​​S0, weigh it, and record its weight as M1; then wipe off the active material layer of the weighed electrode sheet, weigh the current collector, and record it as M0. The areal density of the active material layer = (M1-M0) / S0.

[0065] In this application, the elongation at break of the positive current collector refers to the elongation at break at room temperature.

[0066] Aluminum foil current collectors are an essential component of secondary batteries, and thinning them remains one of the most effective methods to further improve energy density. However, despite reducing costs and increasing energy density, this approach is difficult to implement industrially. The main reasons are as follows: First, thinning the aluminum foil increases its resistance, leading to increased internal resistance and decreased power performance. Second, as aluminum foil is a good thermal conductor, thinning it increases heat generation and makes heat dissipation difficult, increasing safety risks. Third, thinning the aluminum foil reduces its strength, and to further improve energy density, thinner current collectors are often used with higher compaction densities, which can cause the positive electrode to break during rolling, affecting the processing performance of both the positive electrode and the secondary battery.

[0067] Furthermore, high-power batteries require larger discharge currents during use, resulting in higher heat generation during discharge. At high temperatures, the decomposition reaction of the non-aqueous electrolyte at the positive and negative electrode interfaces increases significantly, leading to a substantial increase in both the positive and negative electrode interface impedances and a deterioration in the power performance of the secondary battery. Currently, thickening the aluminum foil current collector is a common measure to obtain high-power batteries.

[0068] Therefore, the current approach of improving the energy density of secondary batteries by thinning the cathode current collector still faces many difficulties in practical applications, such as deterioration of power performance, increased safety hazards, and deterioration of processing performance.

[0069] The inventors of this application made a surprising discovery during the research process: by using a suitable non-aqueous electrolyte, the problems of deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by the thinning of the positive electrode current collector can be solved. Thus, the secondary battery can simultaneously achieve low cost, high energy density, high power performance, good processing performance, and high safety performance.

[0070] Specifically, this application provides a secondary battery.

[0071] A secondary battery, also known as a rechargeable battery or accumulator, is a battery that can be recharged after discharge to reactivate its active materials and continue to be used. The secondary battery in this application can be a lithium secondary battery, particularly a lithium-ion secondary battery. The secondary battery includes an electrode assembly, a non-aqueous electrolyte, and an outer packaging. The outer packaging is used to encapsulate the electrode assembly and the non-aqueous electrolyte. The electrode assembly typically includes a positive electrode, and may also include a negative electrode and a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing lithium ions to pass through. In some embodiments, the positive electrode, the separator, and the negative electrode are manufactured into the electrode assembly using a winding process or a stacking process.

[0072] The positive electrode includes a positive current collector and a positive active material layer located on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector. The negative electrode includes a negative current collector and a negative active material layer located on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative active material layer is disposed on either or both of the two opposite surfaces of the negative current collector. During the charging and discharging process of the secondary battery, lithium ions are inserted and extracted back and forth between the positive and negative electrode plates. The non-aqueous electrolyte includes lithium salts and organic solvents, which are used to conduct lithium ions between the positive and negative electrode plates.

[0073] In the secondary battery of this application, the non-aqueous electrolyte comprises a compound of Formula 1, wherein X and Y each independently represent a fluorine atom, or at least one of the following groups that are partially or fully fluorinated: C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C8 aryl, C1-C10 alkoxy, C2-C10 alkenyloxy, C2-C10 alkynyloxy, C6-C8 aryloxy, and at least one of X and Y represents a fluorine atom.

[0074]

[0075] Based on the total mass of the non-aqueous electrolyte, the mass percentage of the compound shown in Formula 1 is A1%, the thickness of the positive electrode current collector is H μm, the elongation at break of the positive electrode current collector is Q%, and the compaction density of the positive electrode active material layer is P g / cm³. 3 The secondary battery satisfies the following conditions: H is 4 to 14, A1 / H is 0.0015 to 0.20, Q+A1 is 1 to 4, and P / A1 is 2 to 340.

[0076] In this application, the thickness H μm of the positive current collector satisfies that H is between 4 and 14. Optionally, H can be between 4 and 13, 4 and 12, 4 and 11, 4 and 10, 4 and 9, or 4 and 8.

[0077] During their research, the inventors of this application discovered that in a secondary battery employing a thinned positive electrode current collector, when the non-aqueous electrolyte contains the compound shown in Formula 1, and by controlling its content A1%, the thickness H μm of the positive electrode current collector, the elongation at break Q% of the positive electrode current collector, and the compaction density P g / cm³ of the positive electrode active material layer, 3The relationship between these factors allows secondary batteries to simultaneously achieve low cost, high energy density, high power performance, good processing performance, and high safety performance when A1 / H is 0.0015 to 0.20, Q+A1 is 1 to 4, and P / A1 is 2 to 340.

[0078] Although the mechanism is not yet clear, the inventors speculate that the possible reasons include the following.

[0079] First, the compound shown in Formula 1 contains an oxalate group in its molecular structure, which can be preferentially oxidized on the surface of the positive electrode active material compared to organic solvents, and its oxidation product also has the characteristic of low impedance, which helps to form a low impedance positive electrode interface film. At the same time, the B atom in the molecular structure of the compound shown in Formula 1 can also easily and firmly bind with inorganic components such as LiF in the positive electrode interface film, which can accelerate lithium-ion transport and significantly reduce the internal resistance of the battery, so that the secondary battery has high energy density and high power performance, and can perform high current discharge.

[0080] Second, the BO bond in the molecular structure of the compound shown in Formula 1 can interact with Al. 3+ Bonding and forming a passivation film on the surface of the positive electrode current collector helps improve the strength of the positive electrode current collector, enhances the processing performance of the positive electrode sheet, reduces or even avoids strip breakage, and makes the practical application of thinner positive electrode current collectors possible. The compound shown in Formula 1 contains fluorine atoms in its molecular structure, which can bond with Al... 3+ Bonding improves the strength of the positive electrode, enhances its processing performance, reduces or even eliminates breakage, and makes the practical application of thinner positive current collectors possible.

[0081] Third, the compound shown in Formula 1 exhibits high thermal stability, superior to common LiPF6, thus contributing to improved overall heat resistance of the non-aqueous electrolyte. Simultaneously, the compound shown in Formula 1 is less sensitive to moisture than LiPF6, further enhancing the water resistance of the non-aqueous electrolyte, reducing HF formation, and lowering its acidity. Therefore, the non-aqueous electrolyte of this application possesses high thermal and electrochemical stability, thereby reducing decomposition of the non-aqueous electrolyte at high temperatures and lowering battery internal resistance. According to Joule's law, the heat generation of a secondary battery is directly related to its internal resistance. Therefore, reducing the battery's internal resistance also reduces its heat generation, enabling the secondary battery to achieve high energy density while maintaining high power performance and high safety.

[0082] Fourth, the inventors were pleasantly surprised to discover that, since the anionic portion of the compound shown in Formula 1 is easily oxidized, the lithium ions dissociated from its molecular structure can also become active lithium ions, contributing part of the capacity, thereby helping to further improve the energy density of the secondary battery.

[0083] Therefore, when the non-aqueous electrolyte contains the compound shown in Formula 1, it helps to form a passivation film on the surface of the positive electrode current collector, improving the processing performance of the positive electrode sheet and the secondary battery; it also helps to form a low-resistance interface film on the surface of the positive electrode active material, improving the power performance and safety performance of the secondary battery; and it also helps to increase the number of active lithium ions, contributing to the capacity. However, the inventors of this application have found in further research that the content of the compound shown in Formula 1 needs to be reasonably matched with the thickness of the positive electrode current collector, the elongation at break of the positive electrode current collector, and the compaction density of the positive electrode active material layer, in order to reduce the negative impact of thinning the positive electrode current collector on power performance, processing performance, and safety performance, so that the secondary battery can simultaneously achieve low cost, high energy density, high power performance, good processing performance, and high safety performance.

[0084] In this application, the content A1% of the compound shown in Formula 1 and the thickness Hμm of the positive electrode current collector satisfy A1 / H between 0.0015 and 0.20. Therefore, the BO bond energy in the molecular structure of the compound shown in Formula 1 can bond with Al. 3+ Better bonding and formation of a passivation film of suitable thickness on the surface of the positive electrode current collector helps improve the strength of the positive electrode current collector, enhances the processing performance of the positive electrode sheet, and reduces or even avoids strip breakage. When Al / H is less than 0.0015, the positive electrode current collector is thicker, but the content of the compound shown in Formula 1 is low, and there is insufficient compound shown in Formula 1 to bind with Al. 3+ Bonding occurs on the surface of the positive electrode current collector to form a passivation film, resulting in poor processing performance of the positive electrode and the secondary battery. When Al / H is greater than 0.20, the positive electrode current collector is thin and the content of the compound shown in Formula 1 is high, leading to the formation of an excessively thick interface film. As a result, the positive electrode interface impedance and / or negative electrode interface impedance are high, which in turn leads to higher internal resistance and heat generation in the battery, and deteriorates the power performance and safety performance of the secondary battery. Optionally, A1 / H is 0.002 to 0.15, 0.002 to 0.1, 0.002 to 0.08, 0.002 to 0.07, 0.002 to 0.06, 0.002 to 0.05, 0.005 to 0.15, 0.005 to 0.1, 0.005 to 0.08, 0.005 to 0.07, 0.005 to 0.06, 0.005 to 0.05, 0.01 to 0.15, 0.01 to 0.1, 0.01 to 0.08, 0.01 to 0.07, 0.01 to 0.06, or 0.01 to 0.05.

[0085] In this application, the content A1% of the compound shown in Formula 1 and the elongation at break Q% of the positive electrode current collector satisfy Q+A1 being between 1 and 4. Therefore, the BO bond energy in the molecular structure of the compound shown in Formula 1 can bond with Al. 3+Better bonding and formation of a passivation film of suitable thickness on the surface of the positive electrode current collector helps improve the strength of the positive electrode current collector, enhances the processing performance of the positive electrode sheet, and reduces or even avoids strip breakage. When Q+A1 is less than 1, there are not enough compounds as shown in Formula 1 to react with Al. 3+ Bonding and forming a passivation film on the surface of the positive electrode current collector, while the poor ductility of the positive electrode current collector makes it prone to breakage during the rolling process, resulting in poor processing performance of the positive electrode sheet and the secondary battery. When Q+A1 is greater than 4, the positive electrode current collector has high ductility and good pressure resistance, but it is not puncture resistant. When squeezed by sharp materials (such as hard carbon particles with sharp morphology), it is easily damaged and large burrs appear, causing a high risk of internal short circuit in the battery. As a result, the safety performance of the secondary battery cannot be effectively improved. At the same time, a large amount of the compound shown in Formula 1 will also lead to the formation of an excessively thick interface film, resulting in high positive electrode interface resistance and / or negative electrode interface resistance, and poor power performance and safety performance of the secondary battery. Optionally, Q+A1 can be 1.5 to 4, 1.8 to 4, 2.0 to 4, 2.2 to 4, 2.4 to 4, 2.6 to 4, 2.8 to 4, 3.0 to 4, 1.5 to 3.5, 1.8 to 3.5, 2.0 to 3.5, 2.2 to 3.5, 2.4 to 3.5, 2.6 to 3.5, 2.8 to 3.5, or 3.0 to 3.5.

[0086] In this application, the content A1% of the compound shown in Formula 1 is related to the compaction density P g / cm³ of the positive electrode active material layer. 3The P / A1 ratio is between 2 and 340. Therefore, the compound shown in Formula 1 helps to form a low-resistance interface film on the surface of the positive electrode active material, reducing the interface impedance of the positive electrode. At the same time, it also helps the B atoms in the molecular structure of the compound shown in Formula 1 to better combine with the O atoms in the positive electrode active material, thereby reducing the charge transfer impedance of the positive electrode active material and the bulk diffusion resistance of lithium ions. This can reduce the internal resistance and heat generation of the battery and improve the power performance and safety performance of the secondary battery. When P / A1 is less than 2, the compaction density of the positive electrode active material layer is low while the content of the compound shown in Formula 1 is high, resulting in the formation of an excessively thick interfacial film. Consequently, the positive electrode interfacial impedance and / or negative electrode interfacial impedance are high, leading to higher internal resistance and heat generation in the battery, and poor power performance and safety performance of the secondary battery. When P / A1 is greater than 340, the compaction density of the positive electrode active material layer is high while the content of the compound shown in Formula 1 is low. There is not enough compound shown in Formula 1 to form a low-resistance interfacial film on the surface of the positive electrode active material. Furthermore, the charge transfer impedance of the positive electrode active material and the bulk diffusion resistance of lithium ions are high, which leads to increased internal resistance and heat generation in the battery, and poor power performance and safety performance of the secondary battery. Optionally, P / A1 can be 2 to 200, 2 to 100, 2 to 75, 2 to 50, 2 to 35, 2 to 30, 2 to 25, 2 to 20, 2 to 15, 3.5 to 340, 3.5 to 200, 3.5 to 100, 3.5 to 75, 3.5 to 50, 3.5 to 35, 3.5 to 30, 3.5 to 25, 3.5 to 20, 3.5 to 15, 5 to 340, 5 to 200, 5 to 100, 5 to 75, 5 to 50, 5 to 35, 5 to 30, 5 to 25, or 10 to 20.

[0087] In some embodiments, optionally, the secondary battery satisfies the following conditions: H is 4 to 14, A1 / H is 0.01 to 0.05, Q+A1 is 1.5 to 3.5, and P / A1 is 10 to 340. More optionally, the secondary battery satisfies the following conditions: H is 4 to 14, A1 / H is 0.01 to 0.05, Q+A1 is 2.0 to 3.5, and P / A1 is 10 to 340.

[0088] In this application, at least one of X and Y represents a fluorine atom. The presence of a fluorine atom helps to form a thinner fluorinated positive electrode interface film and / or negative electrode interface film, thereby facilitating uniform lithium-ion transport and effectively suppressing lithium dendrite formation. In some embodiments, one of X and Y represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl, phenyl, phenoxy, C1-C5 alkoxy, C2-C5 alkenyloxy, and C2-C5 alkynoxy. Optionally, one of X and Y represents a fluorine atom, and the other represents at least one of the following groups that are partially or fully fluorinated: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, vinyl, propenyl, allyl, butadiene, ethynyl, propynyl, phenyl, methoxy, ethoxy, propoxy, ethyleneoxy, propynyloxy, ethynyloxy, propynyloxy, and phenoxy.

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

[0090] As an example, the compound shown in Formula 1 includes at least one of the following compounds:

[0091]

[0092] In some embodiments, the positive current collector is made of aluminum foil or aluminum alloy foil. To improve the corrosion resistance and strength of the positive current collector, aluminum foil with a purity of 99.99% or higher may be used. As an aluminum alloy foil, in addition to aluminum, it contains at least one element selected from iron, magnesium, zinc, manganese, and silicon. For example, the aluminum alloy foil may be an Al-Fe alloy foil, an Al-Mn alloy foil, or an Al-Mg alloy foil. The mass percentage of aluminum in the aluminum alloy foil may optionally be 95% to 99.5%, more preferably 98% to 99.5%.

[0093] In some embodiments, A1 is 0.02 to 1.8. Optionally, 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 shown in Formula 1 is within a suitable range, it can form a passivation film of appropriate thickness on the surface of the positive electrode current collector, and simultaneously form a low-resistance interface film on the surface of the positive electrode active material. This improves upon the defects caused by thinning of the positive electrode current collector, such as deteriorated power performance, increased safety hazards, and reduced processing performance. Furthermore, it effectively avoids the following situation: when the content of the compound shown in Formula 1 is low, there is insufficient amount of the compound shown in Formula 1 to react with Al. 3+ Bonding occurs on the surface of the positive electrode current collector to form a passivation film, resulting in poor processing performance of the positive electrode and the secondary battery. When the content of the compound shown in Formula 1 is high, the positive electrode interface impedance and / or negative electrode interface impedance increase, the battery internal resistance and heat generation increase, and the power performance and safety performance of the secondary battery deteriorate.

[0094] In some embodiments, Q is 0.5 to 3.5. Optionally, Q is 1 to 3.5, 1.5 to 3.5, 1.8 to 3.5, 2.0 to 3.5, 2.2 to 3.5, 2.4 to 3.5, 2.6 to 3.5, 2.8 to 3.5, or 3.0 to 3.5. When the elongation at break of the positive electrode current collector is within a suitable range, the positive electrode current collector has high strength and good processing performance, and is not prone to breakage. Furthermore, it can effectively avoid the following situations: when the elongation at break of the positive electrode current collector is small, the ductility of the positive electrode current collector is poor, and breakage is likely to occur during the rolling process, leading to a deterioration in the processing performance of the positive electrode sheet and the secondary battery; when the elongation at break of the positive electrode current collector is large, it is not puncture-resistant, and is easily damaged and develops large burrs when subjected to pressure from sharp objects, resulting in a higher risk of internal short circuits in the battery, thus the safety performance of the secondary battery cannot be effectively improved.

[0095] In some embodiments, P is 3.2 to 3.7. Optionally, P is 3.3 to 3.7, 3.4 to 3.7, 3.5 to 3.7, 3.2 to 3.6, 3.3 to 3.6, 3.4 to 3.6, or 3.5 to 3.6. A higher compaction density of the positive electrode active material layer helps to improve the energy density of the secondary battery.

[0096] In some embodiments, when the thickness H μm of the positive electrode current collector satisfies that H is greater than or equal to 11 and less than or equal to 14, specifically, H is 11 to 14, optionally 12 to 14, or 12 to 13, the secondary battery satisfies: A1 / H is 0.005 to 0.15, Q+A1 is 1 to 4, and P / A1 is 2 to 100. Optionally, the secondary battery satisfies: A1 / H is 0.005 to 0.1, Q+A1 is 1.5 to 3.5, and P / A1 is 5 to 75.

[0097] In some embodiments, when the thickness H μm of the positive electrode current collector satisfies that H is 4 or more and 11 or less, optionally 10 or less, 9 or less, or 8 or less, specifically, H is 4 to 11, optionally 4 to 10, 4 to 9, or 4 to 8, the secondary battery satisfies: A1 / H is 0.006 to 0.1, Q+A1 is 1 to 4, and P / A1 is 2 to 100. Optionally, A1 / H is 0.01 to 0.05, Q+A1 is 1.5 to 3.5, and P / A1 is 5 to 75.

[0098] [Lithium salts]

[0099] In some embodiments, the non-aqueous electrolyte includes a first lithium salt, which is lithium hexafluorophosphate (LiPF6) or a combination of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). Lithium hexafluorophosphate has high ionic conductivity, and when its content is within a suitable range, it helps to improve the overall ionic conductivity of the non-aqueous electrolyte, accelerate lithium-ion transport, and improve the capacity retention of the secondary battery. However, lithium hexafluorophosphate has poor thermal stability at high temperatures and decomposes to form PF5. PF5 reacts with water to form HF, which easily corrodes the positive electrode active material and increases battery gas expansion. When the non-aqueous electrolyte contains both the compound shown in Formula 1 and lithium hexafluorophosphate, the compound shown in Formula 1 can react with lithium hexafluorophosphate to form the compound LiPF4C2O4, thereby reducing some of the decomposition of lithium hexafluorophosphate and the formation of HF, thus allowing the secondary battery to maintain good cycle performance. The chemical formula of lithium bis(fluorosulfonyl)imide is F2NO4S2· The N atom in Li is bonded to two electron-withdrawing sulfonyl groups, which fully delocalizes the charge on the N atom. This results in lithium difluorosulfonylimide having a low lattice energy and easy dissociation, thereby improving the ionic conductivity and reducing the viscosity of the non-aqueous electrolyte. Furthermore, lithium difluorosulfonylimide exhibits good high-temperature resistance and is not easily hydrolyzed, enabling the formation of a thinner, lower-impedance, and more thermally stable interfacial film on the surface of the negative electrode active material, thus reducing side reactions between the negative electrode active material and the non-aqueous electrolyte. However, lithium difluorosulfonylimide easily corrodes the positive electrode current collector, therefore its content should not be too high.

[0100] In some embodiments, optionally, the lithium hexafluorophosphate has a mass percentage of A2, where A2 is 6 to 14, based on the total mass of the non-aqueous electrolyte. More optionally, A2 is 6 to 12, 6 to 10, 8 to 14, 8 to 12, or 8 to 10.

[0101] In some embodiments, optionally, the lithium bisfluorosulfonylimide has a mass percentage of A3, where A3 is greater than 0 and less than or equal to 5, based on the total mass of the non-aqueous electrolyte. More optionally, A3 is 0.1 to 2.5, 0.1 to 2, 0.1 to 1.5, 0.1 to 1, 0.2 to 2.5, 0.2 to 2, 0.2 to 1.5, 0.2 to 1, 0.5 to 2.5, 0.5 to 2, 0.5 to 1.5, or 0.5 to 1.

[0102] In some embodiments, optionally, A3 / A2 is below 0.8, more preferably 0.01 to 0.8, 0.05 to 0.8, 0.1 to 0.8, 0.01 to 0.6, 0.05 to 0.6, 0.1 to 0.6, 0.01 to 0.4, 0.05 to 0.4, 0.1 to 0.4, 0.01 to 0.3, 0.05 to 0.3, or 0.1 to 0.3. Thus, the non-aqueous electrolyte is less prone to hydrolysis and also achieves higher thermal stability, while simultaneously contributing to the formation of an interface film with lower impedance.

[0103] In some embodiments, A2 / A1 is 5 to 650, based on the total mass of the non-aqueous electrolyte. Lithium hexafluorophosphate has the characteristic of high ionic conductivity. By reasonably combining the content A1% of the compound shown in Formula 1 with the content A2% of lithium hexafluorophosphate, it is helpful to further improve the capacity retention of the secondary battery while mitigating the problems of deteriorated power performance, increased safety hazards, and deteriorated processing performance caused by the thinning of the positive electrode current collector. Furthermore, it can effectively avoid the following situations: When the content of lithium hexafluorophosphate is high and the content of the compound shown in Formula 1 is low, there may be more PF5 in the non-aqueous electrolyte, which leads to more decomposition reactions in the non-aqueous electrolyte. At the same time, the interfacial film formed by the compound shown in Formula 1 at the positive electrode is not uniform and dense enough, which cannot prevent HF from corroding the positive electrode active material and the series of side reactions caused therefrom. As a result, the secondary battery has a high gas production and heat generation, and the power performance, storage performance and safety performance may deteriorate. When the content of lithium hexafluorophosphate is low and the content of the compound shown in Formula 1 is high, the compound shown in Formula 1 is not easy to completely dissociate in the non-aqueous electrolyte, and the anions and cations are easy to associate, which leads to a decrease in the ionic conductivity of the non-aqueous electrolyte, and the capacity retention rate of the secondary battery may deteriorate. Optionally, A2 / A1 can be 5 to 500, 5 to 300, 5 to 250, 5 to 200, 5 to 150, 5 to 100, 5 to 75, 5 to 50, 10 to 500, 10 to 300, 10 to 250, 10 to 200, 10 to 150, 10 to 100, 10 to 75, 10 to 50, 15 to 500, 15 to 300, 15 to 250, 15 to 200, 15 to 150, 15 to 100, 15 to 75, or 15 to 50.

[0104] In some embodiments, the non-aqueous electrolyte may further include a second lithium salt, which includes at least one selected from lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The second lithium salt can serve as an auxiliary lithium salt, further improving the interfacial properties of the positive and / or negative electrodes, or improving the ionic conductivity or thermal stability of the non-aqueous electrolyte.

[0105] Optionally, the total mass percentage of the second lithium salt in the non-aqueous electrolyte is A4%, where A4 is less than 5%, and more preferably less than 2%, based on the total mass of the non-aqueous electrolyte.

[0106] Optionally, in some embodiments, the second lithium salt comprises lithium difluorophosphate (LiPO2F2), lithium tetrafluorooxalate phosphate (LiTFOP), or a combination thereof; more preferably, the second lithium salt comprises lithium difluorophosphate (LiPO2F2). Lithium difluorophosphate exhibits high electrochemical stability, which can improve the ionic conductivity of non-aqueous electrolytes, enhance the properties of the positive and / or negative electrode interfacial films, and contribute to the construction of stable and low-resistance positive and / or negative electrode interfacial films, thereby effectively reducing the decomposition of non-aqueous electrolytes and further improving the power performance and safety performance of the secondary battery. Optionally, the mass ratio α of lithium difluorophosphate to lithium hexafluorophosphate is 0.01 to 0.15, more preferably 0.01 to 0.1.

[0107] In some embodiments, A1+A2+A3+A4 may optionally be 10 to 20, and more preferably 12 to 16.

[0108] [Organic solvents]

[0109] In some embodiments, the non-aqueous electrolyte comprises an organic solvent, which includes at least one of cyclic carbonate compounds, chain carbonate compounds, and carboxylic acid ester compounds. Optionally, the cyclic carbonate compound may include at least one of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and ethylene ethylene carbonate (VEC). Optionally, the chain carbonate compound may include at least one of methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Optionally, the carboxylic acid ester 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).

[0110] Optionally, in some embodiments, the organic solvent includes at least cyclic carbonate compounds and chain carbonate compounds. When the content of lithium salts such as lithium hexafluorophosphate is high, the viscosity of the non-aqueous electrolyte increases and the ionic conductivity decreases, which is detrimental to lithium ion transport. Cyclic carbonate compounds, due to their higher dielectric constant, can increase the ionic conductivity of the non-aqueous electrolyte, while chain carbonate compounds, due to their lower viscosity, can reduce the viscosity of the non-aqueous electrolyte. Therefore, when the organic solvent includes both cyclic and chain carbonate compounds, it helps to give the non-aqueous electrolyte suitable viscosity and ionic conductivity, thereby facilitating lithium ion transport.

[0111] Cyclic carbonate compounds have high dielectric constants, which helps increase the ionic conductivity of non-aqueous electrolytes. However, they are prone to decomposition reactions, affecting the storage performance of secondary batteries. Therefore, their content needs to be controlled within a suitable range. In some embodiments, the mass percentage of the cyclic carbonate compound is B1%, where B1 is greater than 0 and less than or equal to 20, based on the total mass of the non-aqueous electrolyte. Optionally, B1 is 0.5 to 20, 1 to 20, 2 to 20, 5 to 20, 10 to 20, 12 to 20, 15 to 20, or 15 to 18.

[0112] In some embodiments, the chain carbonate compound comprises B2% by mass, where B2 is 45 to 80% based on the total mass of the non-aqueous electrolyte. Optionally, B2 is 50 to 80%, 55 to 80%, 60 to 80%, or 60 to 75%.

[0113] Carboxylic acid ester compounds have the advantages of low viscosity and high dielectric constant. Their application in non-aqueous electrolytes helps the electrolyte achieve suitable viscosity and ionic conductivity, thereby facilitating lithium-ion transport and improving the rate performance of secondary batteries. While carboxylic acid ester compounds can improve the power performance of secondary batteries, they have poor oxidation resistance and are prone to decomposition during high-charge storage; therefore, their content should not be too high. In some embodiments, the mass percentage of the carboxylic acid ester compound is B3%, where B3 is 0 to 15, based on the total mass of the non-aqueous electrolyte. In some embodiments, B3 can be 0. Optionally, in some embodiments, B3 can be 2 to 15, 2 to 10, 2 to 8, or 2 to 5.

[0114] The organic solvents of this application may also include solvents other than the aforementioned cyclic carbonate compounds, chain carbonate compounds, and carboxylic acid ester compounds. As an example, these other solvents may include sulfone solvents, such as sulfolane (SF), dimethyl sulfone (MSM), ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0115] In some embodiments, the content A1% of the compound shown in Formula 1 and the content B1% of the cyclic carbonate compound satisfy B1 / 20+A1 being 1 to 3, optionally 1 to 2, 1 to 1.8, 1 to 1.6, or 1 to 1.4. A reasonable combination of the content A1% of the compound shown in Formula 1 and the content B1% of the cyclic carbonate compound helps to further improve the capacity retention rate of the secondary battery while mitigating problems such as decreased power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector. Furthermore, it can effectively avoid the following situations: when the content of both the compound shown in Formula 1 and the cyclic carbonate compound is high, the battery internal resistance and gas production are high, which may affect the power performance and storage performance of the secondary battery; when the content of both the compound shown in Formula 1 and the cyclic carbonate compound is low, the ionic conductivity of the non-aqueous electrolyte is low, and there may not be enough compound shown in Formula 1 to form a passivation film on the surface of the positive electrode current collector and a low-resistance interface film on the surface of the positive electrode active material. As a result, the processing performance of the positive electrode sheet may be poor, and the power performance, safety performance and cycle performance of the secondary battery may also deteriorate.

[0116] [additive]

[0117] In some embodiments, the non-aqueous electrolyte may further include additives, such as at least one selected from halogen-substituted cyclic carbonate compounds, nitrile compounds, phosphazene compounds, aromatic hydrocarbons and halogenated aromatic hydrocarbon compounds, isocyanate compounds, acid anhydride compounds, sulfate ester compounds, sulfite ester compounds, sulfonate compounds, and disulfonate compounds. This application does not impose any particular limitation on the types of these additives, as long as they do not impair the spirit of this application. Optionally, the total mass percentage of these additives is less than 5%, more preferably less than 2.5%, based on the total mass of the non-aqueous electrolyte.

[0118] Optionally, in some embodiments, the non-aqueous electrolyte may further comprise fluoroethylene carbonate (FEC) with a mass percentage of C1%, where 0 ≤ C1 ≤ 2.5, based on the total mass of the non-aqueous electrolyte. For example, C1 is a range consisting 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 of the above values. 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.

[0119] For secondary batteries, fluoroethylene carbonate can undergo reductive decomposition at higher potentials, forming a flexible interfacial film on the surface of the negative electrode active material. Simultaneously, it can inhibit the reductive decomposition of organic solvents at lower potentials and prevent the intercalation of organic solvents into the negative electrode active material. Therefore, when non-aqueous electrolytes contain fluoroethylene carbonate, the cycle performance of secondary batteries can be effectively improved. Furthermore, fluoroethylene carbonate is resistant to high-voltage oxidation, which is beneficial for matching with high-voltage positive electrode active materials, thereby further improving the energy density of secondary batteries.

[0120] In some embodiments, the content A1% of the compound shown in 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≤2.5, 0.5≤C1 / A1≤2, 0.5≤C1 / A1≤1.5, or 0.5≤C1 / A1≤1.0.

[0121] When non-aqueous electrolytes contain fluoroethylene carbonate, they can effectively improve the cycle performance of secondary batteries. However, fluoroethylene carbonate is prone to decomposition and the formation of HF, which can damage the positive electrode interface film, corrode the positive electrode active material, and increase the heat and gas generation of the secondary battery. The compound shown in Formula 1 can act 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 of HF to the crystal structure. Therefore, using the compound shown in Formula 1 in combination with fluoroethylene carbonate is beneficial to fully leveraging the further improvement effect of fluoroethylene carbonate on the cycle performance of secondary batteries. Furthermore, rationally controlling the relationship between the content A1% of the compound shown in Formula 1 and the content C1% of fluoroethylene carbonate, ensuring that 0.25≤C1 / A1≤25, can fully leverage the synergistic effect of the compound shown in Formula 1 and fluoroethylene carbonate. This helps to further improve the cycle performance of secondary batteries while mitigating problems such as decreased power performance, increased safety hazards, and deteriorated processing performance caused by thinning of the positive electrode current collector. Meanwhile, fluoroethylene carbonate has a high dielectric constant. By reasonably controlling the relationship between the content A1% of the compound shown in Formula 1 and the content C1% of fluoroethylene carbonate, so that it satisfies 0.25≤C1 / A1≤25, it is also possible to ensure that the anions and cations of the compound shown in Formula 1 form free ions and avoid the association of anions and cations. On the one hand, this improves the ionic conductivity of the non-aqueous electrolyte and improves the cycle performance of the secondary battery. On the other hand, it can also increase the number of active lithium ions.

[0122] In some embodiments, the non-aqueous electrolyte may further include a dehydrating additive. This additive helps reduce the water content of the non-aqueous electrolyte and minimizes a series of side reactions caused by moisture, thereby reducing gas production and heat generation in the secondary battery, resulting in better storage and safety performance. Optionally, in some embodiments, the dehydrating additive includes hexamethyldisilazane (HMDS), tris(trimethylsilyl)phosphate (TMSP), or a combination thereof. These two dehydrating additives, in addition to effectively reducing the water content of the non-aqueous electrolyte, can react with lithium hexafluorophosphate to form lithium difluorophosphate. This reduces lithium hexafluorophosphate decomposition and HF formation, and further stabilizes the positive and / or negative electrode interface films, reducing positive and / or negative electrode interface impedance, thereby contributing to further improvements in the power performance, storage performance, and safety performance of the secondary battery.

[0123] In some embodiments, the water-removing additive has a mass percentage of less than 2%, optionally from 0.05% to 1%, and more preferably from 0.1% to 1%, based on the total mass of the non-aqueous electrolyte.

[0124] The non-aqueous electrolyte of this application can be prepared using methods conventional in the art. For example, the organic solvent, the lithium salt, and the additives can be mixed evenly to obtain the non-aqueous electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the lithium salt and the additives can be added to the organic solvent and mixed evenly to obtain the non-aqueous electrolyte.

[0125] In this application, the components and their contents in the non-aqueous electrolyte can be determined according to methods known in the art. For example, they can be determined by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), etc.

[0126] It should be noted that during the non-aqueous electrolyte testing of this application, the non-aqueous electrolyte can be obtained from a secondary battery. An exemplary method for obtaining the non-aqueous electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cutoff voltage (for safety, the battery is generally left fully discharged), followed by centrifugation. A suitable amount of the centrifuged liquid is then taken as the non-aqueous electrolyte. Alternatively, the non-aqueous electrolyte can be obtained directly from the secondary battery's filling port.

[0127] In this application, the positive electrode active material layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries. 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 modified compounds. 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 modified compounds. Examples of lithium-containing phosphates with an olivine structure may include at least one of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0128] In some embodiments, the positive electrode active material includes materials with the molecular formula Li. a Ni b Co c Mn d Al e M f O g A h The layered material, M represents the transition metal site doped cation, A represents the oxygen site doped anion, 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, g+h=2.

[0129] The molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The layered material can be selectively modified by M cation doping, A anion doping, or by both M cation and A anion doping. The resulting layered material has a more stable crystal structure, making it less likely for lattice oxygen to precipitate and transition metal ions to escape. This reduces a series of side reactions caused by these reactions, thereby further improving the safety and electrochemical performance of the secondary battery, such as cycle performance and kinetic performance.

[0130] In some embodiments, M is selected from at least one of Si, Ti, Mo, V, Ge, Se, Zr, Nb, Ru, Pd, Sb, Ce, Te, and W.

[0131] In some embodiments, A is selected from at least one of F, N, P, and S. Optionally, A is selected from F. After F doping modification, Li a Ni b Co c Mn d Al e M f O g A h The crystal structure is more stable, and lattice oxygen is less likely to precipitate and transition metal ions are less likely to be extracted, which enables secondary batteries to have better safety performance, cycle performance and kinetic performance.

[0132] The values ​​of a, b, c, d, e, f, g, and h satisfy the following condition: that makes Li a Ni b Co c Mn d Al e M f O g A h Maintain electrical neutrality.

[0133] 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.

[0134] In some embodiments, c = 0.

[0135] 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 is scarce in the Earth's crust, difficult to mine, and expensive; therefore, low-cobalt or cobalt-free materials have become an inevitable development trend for cathode active materials. However, cobalt contributes significantly to the lithium-ion diffusion rate of cathode active materials; low-cobalt or cobalt-free materials will reduce the lithium-ion diffusion rate of cathode active materials, affecting the cycle performance of secondary batteries. Researchers have been working to improve the lithium-ion diffusion rate of low-cobalt or cobalt-free cathode active materials, but a good solution has not yet been found.

[0136] During their research, the inventors of this application unexpectedly discovered that the B atoms in the compound structure shown in Formula 1 readily combine with the O atoms in the positive electrode active material, reducing the charge transfer impedance of the positive electrode active material and thus reducing the diffusion resistance of lithium ions within the bulk phase of the positive electrode active material. Therefore, low-cobalt or cobalt-free positive electrode active materials can exhibit significantly improved lithium-ion diffusion rates, allowing lithium ions within the bulk phase of the low-cobalt or cobalt-free positive electrode active material to be replenished to the surface in a timely manner, preventing excessive delithiation on the surface of the low-cobalt or cobalt-free positive electrode active material, thereby stabilizing the crystal structure of the low-cobalt or cobalt-free positive electrode active material. Because the crystal structure of the low-cobalt or cobalt-free positive electrode active material of this application is more stable, it can greatly reduce the probability of problems such as instability in the structural, chemical, or electrochemical properties of the positive electrode active material due to excessive delithiation on the surface of the low-cobalt or cobalt-free positive electrode active material, such as irreversible distortion and increased lattice defects.

[0137] In some embodiments, d = 0 and 0 < e < 0.50. Alternatively, 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.

[0138] 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.

[0139] In some embodiments, 0 < d < 0.50 and 0 < e < 0.50. Alternatively, 0 < d ≤ 0.30 and 0 < e ≤ 0.10.

[0140] In some embodiments, g = 2, h = 0.

[0141] In some embodiments, g = 0, h = 2.

[0142] In some embodiments, 0 < g < 2, 0 < h < 2, and g + h = 2.

[0143] As an example, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A hLayered materials include, but are not limited to, LiNi 0.7 Mn 0.3 O2, LiNi 0.69 Co 0.01 Mn 0.3 O2, LiNi 0.68 Co 0.02 Mn 0.3 O2, LiNi 0.65 Co 0.05 Mn 0.3 O2, LiNi 0.63 Co 0.07 Mn 0.3 O2, LiNi 0.61 Co 0.09 Mn 0.3 At least one of O2.

[0144] Li a Ni b Co c Mn d Al e M f O g A h It can be prepared according to conventional methods in the art. An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, a manganese source, an aluminum source, an M-element precursor, and an A-element precursor are mixed and then sintered. The sintering atmosphere can be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen 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 actual conditions.

[0145] As examples, lithium sources include, but are 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 examples, nickel sources include, but are not limited to, at least one of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate. As examples, cobalt sources include, but are not limited to, at least one of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate. As examples, manganese sources include, but are not limited to, at least one of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate, and manganese acetate. As examples, aluminum sources include, but are not limited to, at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxalate, and aluminum acetate. As examples, precursors of element M include, but are not limited to, at least one of oxides, nitrate compounds, carbonate compounds, hydroxides, and acetate compounds of element M. As an example, the precursors of element A include, but are 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 hydrogen sulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide, and elemental sulfur.

[0146] In some embodiments, based on the total mass of the positive electrode active material layer, the molecular formula is Li a Ni b Co c Mn d Al e M f O g A h The content of layered materials is 80% to 99%. For example, 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 can be any range consisting of 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or higher. Optionally, the molecular formula is Li. a Ni b Co c Mn d Al e M f O g A hThe content of layered material is 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97%, or 95% to 97%.

[0147] In some embodiments, the positive electrode active material layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes at least one selected from superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass percentage of the positive electrode conductive agent is less than 5% based on the total mass of the positive electrode active material layer.

[0148] In some embodiments, the positive electrode active material layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. In some embodiments, the mass percentage of the positive electrode binder is less than 5% based on the total mass of the positive electrode active material layer.

[0149] The positive electrode active material layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0150] In this application, the negative electrode active material layer includes a negative electrode active material, which may be a negative electrode active material known in the art for use in secondary batteries. As an 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. The tin-based material may include at least one of elemental tin, tin oxide, and tin alloy. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0151] In some embodiments, the negative electrode active material layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. 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 percentage of the negative electrode conductive agent is less than 5% based on the total mass of the negative electrode active material layer.

[0152] In some embodiments, the negative electrode active material layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the negative electrode binder is less than 5% based on the total mass of the negative electrode active material layer.

[0153] In some embodiments, the negative electrode active material layer may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc. In some embodiments, the mass percentage of the other additives is less than 2% based on the total mass of the negative electrode active material layer.

[0154] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymer substrate and a metal material layer formed on at least one surface of the polymer substrate. As an example, the metal material may be selected from at least one of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer substrate may be selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0155] The negative electrode active material layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0156] In this application, the separator is disposed between the positive electrode and the negative electrode, mainly to prevent short circuits between the positive and negative electrodes, while allowing lithium ions to pass through. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0157] In some embodiments, the material of the separator may include at least one selected from glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0158] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0159] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0160] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. A non-aqueous electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0161] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and a non-aqueous electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with a non-aqueous electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0162] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0163] Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0164] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0165] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0166] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0167] This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can 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.), electric trains, ships and satellites, energy storage systems, etc.

[0168] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0169] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0170] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0171] Example

[0172] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0173] The secondary batteries in each embodiment and comparative example were prepared according to the following method.

[0174] Preparation of positive electrode sheet

[0175] LiNi, the positive electrode active material 0.65 Co 0.05 Mn 0.3 O2, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of NMP solvent at a mass ratio of 97.5:1.4:1.1 to form a uniform positive electrode slurry. The positive electrode slurry was then uniformly coated onto the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. The thickness H μm of the positive electrode current collector, the elongation at break Q%, and the compaction density P g / cm³ of the positive electrode active material layer were determined. 3 The specific ranges are shown in Table 1 and Table 3, respectively.

[0176] Preparation of negative electrode sheet

[0177] The negative electrode active material graphite, the binder styrene-butadiene rubber (SBR), the thickener sodium carboxymethyl cellulose (CMC-Na), and the conductive agent carbon black (Super P) are mixed thoroughly in an appropriate amount of deionized water at a mass ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the surface of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0178] Separating membrane

[0179] Porous polyethylene (PE) membrane is used as the separator.

[0180] Preparation of non-aqueous electrolyte

[0181] The cyclic carbonate compound, chain carbonate compound, and carboxylic acid ester compound were uniformly mixed according to the compositions shown in Tables 1 and 3 to obtain an organic solvent. Then, the compound shown in Formula 1, fluoroethylene carbonate (FEC), lithium hexafluorophosphate (LiPF6), and lithium bis(fluorosulfonyl)imide (LiFSI) were added to the organic solvent according to the compositions shown in Tables 1 and 3 and mixed uniformly to obtain a non-aqueous electrolyte. In Tables 1 and 3, the content of each component is based on the total mass of the non-aqueous electrolyte; " / " indicates that the corresponding component was not added.

[0182] Preparation of secondary batteries

[0183] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with a non-aqueous electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0184] Test section

[0185] (1) Secondary battery mass energy density test

[0186] At 25℃, the secondary battery was charged at a constant current of 0.33C to 4.25V, and then charged at a constant voltage until the current reached 0.05C. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 0.33C to 2.8V, yielding the discharge energy. The gravimetric energy density of the secondary battery (Wh / Kg) = discharge energy / mass of the secondary battery.

[0187] (2) Secondary battery power performance test

[0188] At 25℃, the secondary battery is charged at a constant current of 0.1C to 4.25V, and then charged at a constant voltage until the current reaches 0.05C, at which point the secondary battery is fully charged. The secondary battery is then discharged at a constant current of 1C for approximately 30 minutes, and its state of charge (SOC) is adjusted to 50%. The voltage of the secondary battery at this point is recorded as V0. The secondary battery is then discharged at a current of 4C I1 for 30 seconds, with a sampling time of 0.1 seconds; the voltage at the end of the discharge is recorded as V1. The internal resistance of the secondary battery, DCR, is calculated as (V0 - V1) / I1. The lower the internal resistance of the secondary battery, the better its power performance.

[0189] (3) Safety performance test of secondary battery hot box

[0190] At 25℃, the secondary battery was charged at a constant current of 0.1C to 4.25V, and then charged at 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 well-sealed high-temperature chamber, and the temperature was increased to 100℃ at a rate of 5℃ / min and held for 1 hour. Then, the temperature was increased to 105℃ at a rate of 5℃ / min and held for 30 minutes. After that, the temperature was increased by 5℃ at a rate of 5℃ / min and held for 30 minutes each time, until the secondary battery failed. The highest temperature T before the secondary battery failed was recorded. max T max The higher the value, the better the thermal safety performance of the secondary battery.

[0191] (4) Secondary battery cycle performance test

[0192] At 45℃, the secondary battery was charged at a constant current of 1C to 4.25V, and then charged at a constant voltage until the current reached 0.05C. At this point, the secondary battery was fully charged, and the charging capacity was recorded, which is the first charge capacity. After the secondary battery was left to stand for 5 minutes, it was discharged at a constant current of 1C to 2.8V. This completes one charge-discharge cycle, and the discharge capacity was recorded, which is the first discharge capacity. The secondary battery was subjected to cyclic 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℃ = discharge capacity after 600 cycles / discharge capacity of the first cycle × 100%.

[0193] (5) Secondary battery storage performance test

[0194] At 60℃, the secondary battery is charged at a constant current of 1C to 4.25V, and then charged at a constant voltage until the current reaches 0.05C. The volume of the secondary battery at this point is measured using the water displacement method and recorded as V0. The secondary battery is then placed in a 60℃ constant temperature chamber and stored for 30 days. After removal, the volume of the secondary battery is measured again using the water displacement method and recorded as V1. The volume expansion rate (%) of the secondary battery after 30 days of storage at 60℃ is calculated as [(V1-V0) / V0]×100%.

[0195] Table 1 shows the positive electrode and non-aqueous electrolyte parameters for Examples 1-1 to 1-33 and Comparative Examples 1-1 to 1-4. Table 2 shows the test results obtained for Examples 1-1 to 1-33 and Comparative Examples 1-1 to 1-4 according to the above performance test methods.

[0196] Table 3 shows the positive electrode and non-aqueous electrolyte parameters for Examples 2-1 to 2-32 and Comparative Examples 2-1 to 2-3. Table 4 shows the test results obtained for Examples 2-1 to 2-32 and Comparative Examples 2-1 to 2-3 according to the above performance test methods.

[0197]

[0198]

[0199]

[0200]

[0201]

[0202]

[0203]

[0204]

[0205] Based on the test results in Tables 1 and 2, it can be seen that in secondary batteries using thinned positive electrode current collectors, when the non-aqueous electrolyte contains the compound shown in Formula 1 and its content A1%, the thickness H μm of the positive electrode current collector, the elongation at break Q% of the positive electrode current collector, and the compaction density P g / cm³ of the positive electrode active material layer are all related to the following parameters: 3 When A1 / H is 0.0015 to 0.20, Q+A1 is 1 to 4 and P / A1 is 2 to 340, the secondary battery can simultaneously achieve high energy density, low internal resistance, high thermal safety performance, high capacity retention and low volume expansion rate.

[0206] Based on the test results of Examples 1-1 to 1-10 and Comparative Examples 1-2, it can be seen that when Al / H is less than 0.0015 and / or P / Al is greater than 340, there are not enough compounds of Formula 1 to react with Al. 3+ The bonding and bonding form a passivation film on the surface of the positive electrode current collector and a low-resistance interface film on the surface of the positive electrode active material. Therefore, compared with Comparative Example 1-1, it does not effectively improve the negative impact of the thinning of the positive electrode current collector on power performance and safety performance, and the increase in the capacity retention rate of the secondary battery is also limited.

[0207] Based on the test results of Examples 1-1 to 1-10 and Comparative Examples 1-3 to 1-4, it can be seen that when Q+A1 is greater than 4, A1 / H is greater than 0.20 and / or P / A1 is less than 2, excessive amounts of the compound shown in Formula 1 will cause the positive electrode interface impedance and / or negative electrode interface impedance to increase instead of decrease. As a result, the internal resistance of the secondary battery is high and the capacity retention rate is poor. Although the compound shown in Formula 1 can contribute some active lithium ions and slightly increase the energy density of the secondary battery, the oxidation and decomposition of anions leads to a high amount of gas generated inside the battery and a significant deterioration in the thermal box safety performance.

[0208] Based on the test results in Tables 3 and 4, it can be seen that in secondary batteries using thinned positive electrode current collectors, when the non-aqueous electrolyte contains the compound shown in Formula 1 and its content A1%, the thickness H μm of the positive electrode current collector, the elongation at break Q% of the positive electrode current collector, and the compaction density P g / cm³ of the positive electrode active material layer are all related to the following parameters: 3 When A1 / H is 0.0015 to 0.20, Q+A1 is 1 to 4 and P / A1 is 2 to 340, the secondary battery can simultaneously achieve high energy density, low internal resistance, high thermal safety performance, high capacity retention and low volume expansion rate.

[0209] Based on the test results of Examples 2-1 to 2-9 and Comparative Example 2-2, it can be seen that when Al / H is less than 0.0015, there are not enough compounds of Formula 1 to react with Al. 3+ The bonding and bonding form a passivation film on the surface of the positive electrode current collector and a low-resistance interface film on the surface of the positive electrode active material. Therefore, compared with Comparative Example 2-1, it does not effectively improve the negative impact of the thinning of the positive electrode current collector on power performance and safety performance, and the increase in the capacity retention rate of the secondary battery is also limited.

[0210] Based on the test results of Examples 2-1 to 2-9 and Comparative Example 2-3, it can be seen that when A1 / H is greater than 0.20, P / A1 is less than 2 and Q+A1 is greater than 4, excessive amounts of the compound shown in Formula 1 will cause the positive electrode interface impedance and / or negative electrode interface impedance to increase instead of decrease. As a result, the internal resistance of the secondary battery is high and the capacity retention rate is poor. Although the compound shown in Formula 1 can contribute some active lithium ions and slightly increase the energy density of the secondary battery, the oxidation and decomposition of anions leads to a high amount of gas generated inside the battery and a significant deterioration in the thermal box safety performance.

[0211] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery comprising a positive electrode sheet including a positive electrode current collector and a positive electrode active material layer on at least one surface of the positive electrode current collector, and a nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution includes a compound represented by Formula 1, X and Y each independently represent a fluorine atom, or at least one of X and Y represents a fluorine atom, and the other represents at least one selected from the group consisting of a C1-C10 alkyl group, a C2-C10 alkenyl group, a C2-C10 alkynyl group, a C6-C8 aryl group, a C1-C10 alkoxy group, a C2-C10 alkenyloxy group, a C2-C10 alkynyloxy group, and a C6-C8 aryloxy group, which are partially or entirely fluorinated, the mass percentage content of the compound represented by Formula 1 is A1% based on the total mass of the nonaqueous electrolyte solution, A1 is 0.02 to 0.5, the nonaqueous electrolyte solution further includes lithium hexafluorophosphate, lithium bisfluorosulfonylimide, and lithium difluorophosphate, the mass percentage content of the lithium hexafluorophosphate is A2%, the mass percentage content of the lithium bisfluorosulfonylimide is A3% based on the total mass of the nonaqueous electrolyte solution, A2 is 6 to 14, A3 is greater than 0 and less than or equal to 5, A3 / A2 is 0.8 or less, A2 / A1 is 15 to 650, the mass ratio α of the lithium difluorophosphate to the lithium hexafluorophosphate is 0.01 to 0.1, the nonaqueous electrolyte solution further includes a cyclic carbonate compound and a chain carbonate compound, the mass percentage content of the cyclic carbonate compound is B1%, the mass percentage content of the chain carbonate compound is B2% based on the total mass of the nonaqueous electrolyte solution, B1 is 0.5 to 20, and B2 is 55 to 80, the positive electrode current collector is an aluminum foil or an aluminum alloy foil, the thickness of the positive electrode current collector is H μm, H is 4 to 13, the elongation at break of the positive electrode current collector is Q%, and Q is 2.0 to 3.

5. 2.The secondary battery according to claim 1, wherein A1 is 0.05 to 0.5; and / or, H is 9 to 13. A1 / H is 0.002 to 0.

1. Formula 1 A1 / H is 0.005 to 0.

1. P is 3.4 to 3.

7. P / A1 is 6.6 to 175. P / A1 is 6.6 to 100. P / A1 is 6.6 to 75. Q is 2.2 to 3.

5. The positive electrode active material layer includes a positive electrode active material including a lithium transition metal oxide and a modified compound thereof, and a compaction density of the positive electrode active material layer is P g / cm3 3 , P is 3.2 to 3.

7. Q+A1 is 2.2 to 4. Q+A1 is 2.2 to 3.

5. Q+A1 is 2.4 to 3.

5.

3. The secondary battery according to claim 1, wherein The secondary battery satisfies: H is 11 to 13, A1 / H is 0.005 to 0.042, Q+A1 is 2.2 to 4, and P / A1 is 6.6 to 100.

4. The secondary battery according to claim 3, wherein The secondary battery satisfies: H is 11 to 13, A1 / H is 0.005 to 0.042, Q+A1 is 2.2 to 3.5, and P / A1 is 6.6 to 75.

5. The secondary battery according to claim 1, wherein The secondary battery satisfies: H is 4 to 11, A1 / H is 0.006 to 0.1, Q+A1 is 2.2 to 4, and P / A1 is 6.6 to 100.

6. The secondary battery according to claim 1, wherein The secondary battery satisfies:

7. The secondary battery according to claim 6, wherein ​ 8. The secondary battery according to claim 7, wherein ​ 9. The secondary battery according to claim 1, wherein ​ 10. The secondary battery according to claim 1, wherein ​ 11. The secondary battery according to claim 10, wherein ​ 12. The secondary battery according to claim 11, wherein ​ 13. The secondary battery according to claim 1, wherein ​ ​ 14. The secondary battery according to claim 13, wherein ​ ​ 15. The secondary battery according to claim 1, wherein ​ ​ 16. The secondary battery according to claim 15, wherein ​ H is 9 to 11, A1 / H is 0.01 to 0.05, Q+A1 is 2.2 to 3.5, and P / A1 is 6.6 to 75.

17. The secondary battery according to claim 1, wherein A3 / A2 is 0.05 to 0.

3.

18. The secondary battery according to claim 1, wherein A2 / A1 is 15 to 300.

19. The secondary battery according to claim 1, wherein B1 / 20+A1 is 1 to 1.

4.

20. The secondary battery according to claim 1, wherein B1 is 15 to 18.

21. The secondary battery according to claim 1, wherein The cyclic carbonate compound includes at least one of ethylene carbonate, propylene carbonate, vinylene carbonate, and vinyl ethylene carbonate.

22. The secondary battery of claim 1, wherein, The chain carbonate compound includes at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

23. The secondary battery of claim 1, wherein, The nonaqueous electrolyte further includes a carboxylic acid ester compound, the mass percentage content of the carboxylic acid ester compound being B3%, B3 being 2 to 15.

24. The secondary battery according to claim 23, wherein The carboxylic acid ester compound includes at least one of methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

25. The secondary battery according to claim 1, wherein The nonaqueous electrolyte further includes an additive, the additive including at least one of a halogen-substituted cyclic carbonate compound, a nitrile compound, a phosphazene compound, an aromatic hydrocarbon and a halogenated aromatic hydrocarbon compound, an isocyanate compound, an anhydride compound, a sulfate compound, a sulfite compound, a sulfonate compound, and a disulfonate compound, the total mass percentage content of the additive being 5% or less based on the total mass of the nonaqueous electrolyte.

26. The secondary battery of claim 25, wherein, The nonaqueous electrolyte further includes fluorinated ethylene carbonate, the mass percentage content of the fluorinated ethylene carbonate being C1% based on the total mass of the nonaqueous electrolyte.

27. The secondary battery according to claim 26, wherein 0 < C1 ≤ 2.5; and / or, 0.25 ≤ C1 / A1 ≤ 25.

28. The secondary battery of claim 27, wherein, 0＜C1≤2.0。 29. The secondary battery of claim 27, wherein, 0.5 ≤ C1 / A1 ≤ 10.

30. The secondary battery of claim 1, wherein, The nonaqueous electrolyte further includes a water-removing additive, the water-removing additive including at least one of hexamethyldisilazane and tris(trimethylsilyl) phosphate.

31. The secondary battery according to claim 30, wherein The mass percentage content of the water-removing additive is 2% or less based on the total mass of the nonaqueous electrolyte.

32. The secondary battery of claim 31, wherein, The mass percentage content of the water-removing additive is 0.05% to 1% based on the total mass of the nonaqueous electrolyte.

33. The secondary battery of claim 1, wherein, X and Y satisfy one of the following conditions (1) to (3): (1) X and Y each represent a fluorine atom; (2) one of X and Y represents a fluorine atom, and the other represents at least one of the following group consisting of a partially fluorinated or fully fluorinated C1-C5 alkyl group, C2-C5 alkenyl group, C2-C5 alkynyl group, phenyl group, phenoxy group, C1-C5 alkoxy group, C2-C5 alkenyloxy group, and C2-C5 alkynyloxy group; (3) one of X and Y represents a fluorine atom, and the other represents at least one of the following group consisting of a partially fluorinated or fully fluorinated methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, ethenyl group, propenyl group, allyl group, butadienyl group, ethynyl group, propynyl group, phenyl group, methoxy group, ethoxy group, propoxy group, ethenyloxy group, propenyloxy group, ethynyloxy group, propynyloxy group, and phenoxy group.

34. The secondary battery of claim 1, wherein, The compound represented by Formula 1 includes at least one of the following compounds, 。 35. The secondary battery according to claim 1, wherein the positive electrode active material further comprises a lithium-containing phosphate of an olivine structure and a modified compound thereof.

36. A battery module comprising the secondary battery according to any one of claims 1 to 35.

37. A battery pack comprising one of the secondary battery according to any one of claims 1 to 35, the battery module according to claim 36.

38. An electric device comprising at least one of the secondary battery according to any one of claims 1 to 35, the battery module according to claim 36, the battery pack according to claim 37.

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