An electrolyte and its secondary battery, battery module, battery pack and electrical device

Abstract

This application provides an electrolyte comprising an organic solvent, an electrolyte lithium salt, and additives; wherein the organic solvent comprises a fluorinated solvent; the electrolyte lithium salt comprises a fluorosulfonylimide lithium salt; and the additives comprise lithium halide salts. The electrolyte of this application exhibits good conductivity and flame retardancy, and lithium-ion batteries containing this electrolyte possess at least one of improved energy density, safety performance, output performance, and cycle performance.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to an electrolyte and a secondary battery, battery module, battery pack and power device containing the electrolyte. Background Technology

[0002] With the widespread use of electric vehicles and various portable electronic products, lithium-ion batteries have become the preferred energy storage device due to their advantages such as rapid charging and discharging and no memory effect. This has led to higher requirements for the performance of lithium-ion batteries (such as energy density, safety performance, output performance, cycle performance, lifespan, and operating temperature range). In particular, the safety performance of lithium-ion batteries is receiving increasing attention.

[0003] Currently, numerous improvement schemes have been proposed in this field to improve the performance of lithium-ion batteries. However, for lithium-ion batteries, outstanding performance in a single area is not enough to meet the needs; the field requires lithium-ion batteries with good safety, balanced performance, and other comprehensive advantages. Summary of the Invention

[0004] This application was made in view of the above-mentioned problems, and its object is to provide an electrolyte. The electrolyte of this application can improve the overall performance of lithium-ion batteries.

[0005] To achieve the above objectives, this application provides an electrolyte, as well as a secondary battery, battery module, battery pack, and electrical device containing the electrolyte.

[0006] The first aspect of this application provides an electrolyte comprising an organic solvent, an electrolyte lithium salt, and additives; wherein the organic solvent comprises a fluorinated solvent; the electrolyte lithium salt comprises a fluorosulfonylimide lithium salt; and the additives comprise lithium halide salts. The electrolyte of this application has improved conductivity and flame retardancy, and further improves the energy density, first-cycle efficiency, cycle and output performance of lithium-ion secondary batteries, while suppressing lithium dendrite growth.

[0007] In any embodiment, the fluorosulfonylimide lithium salt, the lithium halide salt, and the fluorinated solvent have the following relationship:

[0008] t = [(k*a*c) / (k*a+c)] / b, and the value of t is in the range of 0.0004 to 0.1000, optionally in the range of 0.0190 to 0.0400.

[0009] Where k is the molar concentration of the electrolyte lithium salt, in mol / L; a is the molar percentage of fluorosulfonylimide lithium salt based on the total molar amount of the electrolyte lithium salt; b is the weight percentage of fluorinated solvent based on the total weight of organic solvent; c is the weight percentage of lithium halide salt based on the total weight of the electrolyte; a, b, c, and k are all non-zero. When the contents of fluorinated solvent, fluorosulfonylimide lithium salt, and lithium halide in the electrolyte conform to the above relationships and parameter ranges, the electrolyte performance is good, and the overall performance of the lithium-ion secondary battery is good.

[0010] In any embodiment, the content of the fluorinated solvent is 20% by weight or more, optionally 50% by weight or more, and more preferably 80% by weight or more, based on the total weight of the organic solvent. By increasing the content of the fluorinated solvent, the overall performance of the electrolyte can be further improved.

[0011] In any embodiment, the molar concentration of the electrolyte lithium salt is from 0.5 mol / L to 8 mol / L, optionally from 1.5 mol / L to 4 mol / L. Electrolyte salts within the above range can further improve the performance of the electrolyte (e.g., in particular, conductivity).

[0012] In any embodiment, the content of the lithium halide salt is from 0.05 wt% to 10 wt% based on the total weight of the electrolyte, optionally from 0.5 wt% to 7 wt%, and more preferably from 1 wt% to 6 wt%. Selecting the content of the lithium halide salt can further improve the performance of the electrolyte.

[0013] In any embodiment, based on the total molar amount of the electrolyte lithium salt, the molar percentage of the fluorosulfonylimide lithium salt is at least 30%, optionally at least 60%, and more preferably at least 90%. Keeping the proportion of the fluorosulfonylimide lithium salt in the electrolyte lithium salt within the above range can further improve the performance of the electrolyte.

[0014] In any embodiment, the fluorinated solvent is selected from at least one of fluorocarbonates, fluorophosphates, and fluoroethers; optionally, the fluorinated solvent is selected from at least one of fluorocarbonates and fluoroethers. By selecting the above-mentioned types of fluorinated solvents, this application further improves the aforementioned performance of the electrolyte and the battery.

[0015] In any embodiment, the fluorocarbonate is selected from at least one of fluoroethylene carbonate, fluoromethyl ethyl carbonate, difluoroethylene carbonate, 4-trifluoromethyl ethylene carbonate, and di(2,2,2-trifluoroethyl) carbonate; the fluorophosphate is selected from at least one of tris(2,2,2-difluoroethyl) phosphate and tris(2,2,2-trifluoroethyl) phosphate; and the fluoroether is selected from at least one of hydrofluoroether, 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and nonafluoroisobutyl methyl ether.

[0016] In any embodiment, the fluorinated solvent is selected from at least one of fluoroethylene carbonate, fluoromethyl ethyl carbonate, and hydrofluoroether; optionally, the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoromethyl ethyl carbonate, and hydrofluoroether; more preferably, the fluorinated solvent is a mixture of fluoroethylene carbonate, fluoromethyl ethyl carbonate, and hydrofluoroether.

[0017] By further selecting fluorinated solvents, the performance of the electrolyte of this application and the battery containing the electrolyte is further improved.

[0018] In any embodiment, when the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether, the content of the fluoroethylene carbonate is 10% to 50%, optionally 20% to 40%, based on the total weight of the fluorinated solvent; and / or, the content of the hydrofluoroether is 10% to 50%, optionally 20% to 40%; and / or, the content of the fluoroethyl methyl carbonate is 0% to 80%, optionally 20% to 60%. The amounts of each fluorinated solvent within the above ranges can further improve the performance of the electrolyte and its battery.

[0019] In any embodiment, the lithium halide salt is selected from at least one of lithium iodide, lithium bromide, lithium chloride, and lithium fluoride; optionally, it is at least one of lithium iodide and lithium bromide. By selecting a lithium halide salt, the performance of the electrolyte can be further improved, which is particularly beneficial for suppressing the growth of lithium dendrites.

[0020] In any embodiment, the fluorosulfonylimide lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide, and lithium bis(perfluoro-1-butyryl)imide; optionally, it is at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. Further selection of the fluorosulfonylimide lithium salt can improve the performance of the electrolyte and its battery in this application.

[0021] In any embodiment, the organic solvent further includes a carbonate solvent; optionally, the carbonate solvent is selected from at least one of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethylene carbonate, and propylene carbonate. By including the above-mentioned organic solvent, it is possible to improve the performance of the electrolyte while reducing costs.

[0022] In any embodiment, the electrolyte lithium salt further includes at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium perchlorate. By further selecting and adding the above-mentioned electrolyte lithium salt, the technical effects of this application can be achieved while controlling costs.

[0023] In any embodiment, the electrolyte further includes at least one of a film-forming additive, a flame-retardant additive, an overcharge prevention additive, and a conductive additive. The addition of these additives can specifically further improve the performance of the electrolyte.

[0024] A second aspect of this application provides a secondary battery comprising the electrolyte described in the first aspect.

[0025] A third aspect of this application provides a battery module that includes the secondary battery described in the second aspect.

[0026] A fourth aspect of this application provides a battery pack that includes the battery module described in the third aspect above.

[0027] The fifth aspect of this application provides an electrical device comprising at least one selected from the second aspect of this application, the third aspect of this application, or the fourth aspect of this application.

[0028] The electrolyte of this application achieves at least the following effects: the electrolyte has good conductivity and flame retardancy, and the lithium-ion battery containing the electrolyte has at least one of improved energy density, safety performance, output performance, and cycle performance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0030] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0031] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0032] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0033] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0034] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0037] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrolyte, secondary battery, battery module, battery pack, and electrical device of this application. 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.

[0038] 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.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0040] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0041] 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.

[0042] 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.

[0043] 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).

[0044] With the widespread use of electric vehicles and various portable electronic products, lithium-ion rechargeable batteries, as the preferred energy storage device for such devices, have become a focus of attention in terms of achieving long-lasting battery life and energy storage. Therefore, there is a need in this field for lithium-ion batteries with higher energy density to achieve longer battery life and energy storage, and increasing the operating voltage is one method to improve the energy density of lithium-ion batteries.

[0045] Electrolytes are a crucial component of lithium-ion batteries and a key focus for those skilled in the art. Electrolytes generally consist of solvents, electrolyte salts, and (optionally) various additives. Currently, widely used solvents include carbonates, carboxylic esters, and ethers, while electrolyte salts primarily include LiPF6, LiAsF6, LiBF4, and LiClO4. However, these solvents and / or electrolyte salts are generally unsuitable for high operating voltages (e.g., above 4.2V) because electrolytes based on these solvents and / or salts undergo oxidative decomposition at such voltages, leading to a decline in overall battery performance. Furthermore, the safety of high-voltage lithium-ion batteries decreases with increasing operating voltage. In addition, the inherent flammability, explosiveness, and decomposition of traditional solvents and electrolytes, as mentioned above, further exacerbate safety hazards.

[0046] To obtain safe high-voltage electrolytes, various attempts have been made in this field, such as changing the solvent, electrolyte salt, or adding functional additives. Fluorinated solvents have excellent chemical stability and, as additives or solvents, help improve the flame retardancy of electrolytes and can modify the oxidative decomposition voltage of electrolytes. Using organic fluorinated lithium salts (such as lithium bis(SO2F)2, LiFSI) as electrolyte salts, partially or completely replacing commonly used inorganic lithium salts (such as LiPF6), helps to achieve better chemical stability of high-voltage electrolytes.

[0047] While the aforementioned efforts have improved the performance and safety of electrolytes at high operating voltages to some extent, one-sided performance improvements cannot meet the industry's demand for high-performance lithium-ion batteries—because what the industry needs are lithium-ion batteries that achieve a careful balance between various performance characteristics (such as energy density, safety, output performance, and cycle performance) and have good overall performance.

[0048] In view of the above-mentioned issues, this application provides a high-voltage electrolyte that improves safety performance while also taking into account other performance aspects, thus achieving the goal of balanced electrolyte performance and good overall performance.

[0049] electrolyte

[0050] In one embodiment of this application, an electrolyte is provided, comprising an organic solvent, an electrolyte lithium salt, and an additive; wherein the organic solvent comprises a fluorinated solvent; the electrolyte lithium salt comprises a fluorosulfonylimide lithium salt; and the additive comprises a lithium halide salt.

[0051] In this application, the electrolyte lithium salt includes fluorosulfonylimide lithium salts but excludes the lithium halide salts; in other words, the electrolyte lithium salt includes fluorosulfonylimide lithium salts, and optionally includes other suitable lithium salts besides fluorosulfonylimide lithium salts and lithium halide salts. However, it should be understood that the electrolyte of this application includes lithium halide salts.

[0052] The inventors have discovered that the electrolyte of this application possesses excellent electrical conductivity and flame retardant properties, thereby improving the safety of lithium-ion batteries. Furthermore, by employing the electrolyte of this application, lithium-ion batteries can achieve excellent overall performance, such as higher energy density, higher initial specific capacity, and better cycle performance.

[0053] Although the mechanism is not yet clear, the inventors have also discovered that there is a synergistic effect between the fluorinated solvent, the fluorosulfonyl imide lithium salt and the halide lithium salt contained in the electrolyte of this application, which can significantly suppress the unwanted lithium dendrite growth in lithium-ion secondary batteries, thereby further improving safety.

[0054] Furthermore, the inventors have discovered that the electrolyte of this application can also improve the first-cycle efficiency of lithium-ion batteries. In particular, the first-cycle efficiency of lithium-ion batteries containing the electrolyte of this application is above 85%. Such a high first-cycle efficiency indicates that the electrolyte of this application can reduce the initial irreversible capacity loss of lithium-ion batteries and further improve the energy density of the batteries.

[0055] As used in this article, the term "first-cycle efficiency," also known as "first-cycle coulombic efficiency," refers to the percentage of discharge capacity to charge capacity in a lithium-ion battery during its first charge-discharge cycle.

[0056] As used herein, the term "first-cycle specific capacity" refers to the discharge specific capacity during the first charge-discharge cycle.

[0057] In some embodiments, the fluorosulfonylimide lithium salt, the lithium halide salt, and the fluorinated solvent in the electrolyte of this application have the following relationship:

[0058] t = [(k*a*c) / (k*a+c)] / b, and the value of t is in the range of 0.0004 to 0.1000, optionally in the range of 0.0190 to 0.0400.

[0059] in,

[0060] k is the molar concentration of the electrolyte lithium salt, in mol / L.

[0061] a is the molar percentage of fluorosulfonylimide lithium salt based on the total molar amount of the electrolyte lithium salt.

[0062] b is the weight percentage of fluorinated solvents based on the total weight of organic solvents.

[0063] c is the weight percentage of lithium halide salts based on the total weight of the electrolyte.

[0064] a, b, c, and k are all non-zero.

[0065] In some implementations, the value of t is in the range of 0.0190-0.0210, 0.0193-0.0200, 0.0195-0.0200, 0.0196-0.0200, or 0.0197-0.0200.

[0066] The inventors of this application have discovered that when the fluorinated solvent, the electrolyte lithium salt, and the halide lithium salt in the electrolyte conform to the above-mentioned relationship, good performance can be achieved, such as improved safety (e.g., flame retardancy and suppression of dendrite growth) and improved conductivity; and the lithium-ion battery containing this electrolyte has good energy density, output performance, cycle performance, and especially high first-cycle efficiency.

[0067] In some embodiments, the electrolyte of this application contains 20% by weight or more of the fluorinated solvent, based on the total weight of the organic solvents; optionally, 50% by weight or more; and more preferably 80% by weight or more. In some embodiments, the content of the fluorinated solvent may optionally be 90% by weight or more, based on the total weight of the organic solvents.

[0068] In some embodiments, the content of the fluorinated solvent, based on the total weight of the organic solvent, is 20% by weight or more, 30% by weight or more, 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more. In some embodiments, the content of the fluorinated solvent, based on the total weight of the organic solvent, is 100% by weight; in this case, the organic solvent consists of the fluorinated solvent.

[0069] When the content of fluorinated solvent in the organic solvent is within the above range, the conductivity and flame retardancy of the electrolyte can be further improved, and the overall performance of the lithium-ion battery containing the electrolyte (e.g., energy density, first-cycle specific capacity, first-cycle efficiency, capacity retention, etc.) can be further improved.

[0070] In some embodiments, the molar concentration of the electrolyte lithium salt in the electrolyte of this application is from 0.5 mol / L to 8 mol / L, and optionally from 1.5 mol / L to 4 mol / L.

[0071] In some embodiments, the electrolyte lithium salt is present in an amount of 0.5 mol / L to 8 mol / L, optionally 0.5 mol / L to 5 mol / L, more preferably 1 mol / L to 4 mol / L, even more preferably 1.5 mol / L to 4 mol / L, and even more preferably 2 mol / L to 4 mol / L. In some embodiments, the electrolyte lithium salt is present in an amount of 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, or 8 mol / L; or, in some embodiments, the content of the electrolyte lithium salt is within the range of any two of the above values.

[0072] The inventors discovered that when the content of the electrolyte lithium salt is within the above-mentioned range, the viscosity of the electrolyte is moderate, which is beneficial to improving the conductivity of the electrolyte. However, when the concentration of the electrolyte lithium salt is too high, the overall concentration of the electrolyte increases, but the degree of dissociation of the salt in the electrolyte decreases, and the viscosity of the electrolyte also increases, which in turn leads to a decrease in the conductivity of the electrolyte.

[0073] In this article, the concentration units “M” and “mol / L” are used interchangeably.

[0074] In some embodiments, the content of the lithium halide salt in the electrolyte of this application is from 0.05% to 10% by weight, optionally from 0.5% to 7% by weight, and more preferably from 1% to 6% by weight, based on the total weight of the electrolyte.

[0075] In some embodiments, optionally, the content of the lithium halide salt, based on the total weight of the electrolyte, may be 1% to 4% by weight, more preferably 2% to 4% by weight. In some embodiments, the content of the lithium halide salt, based on the total weight of the electrolyte, is present in amounts of 0.05% by weight, 1% by weight, 1.5% by weight, 2% by weight, 2.5% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, or 10% by weight; or in some embodiments, the content of the lithium halide salt is within the range of any two of the above values.

[0076] By controlling the content of lithium halide salts in the electrolyte within the above-mentioned range, lithium-ion secondary batteries exhibit excellent overall performance, and in particular, they can achieve an ideal effect of suppressing dendrite growth.

[0077] In some embodiments, the fluorosulfonamide lithium salt has a molar percentage of at least 30%, optionally at least 60%, and more preferably at least 90%, based on the total molar amount of the electrolyte lithium salt.

[0078] In some embodiments, the molar percentage of the fluorosulfonylimide lithium salt, based on the total molar amount of the electrolyte lithium salt, is at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, or at least 95%. In some embodiments, the molar percentage of the fluorosulfonylimide lithium salt, based on the total molar amount of the electrolyte lithium salt, is 100%; in other words, the electrolyte lithium salt is composed of the fluorosulfonylimide lithium salt.

[0079] When the molar percentage of fluorosulfonylimide lithium salt is within the above range, it can further improve the thermal stability of the electrolyte, broaden the electrochemical window, and enhance the cycle performance and rate performance of the battery.

[0080] In some embodiments, the fluorinated solvent in the electrolyte of this application is selected from at least one of fluorocarbonates, fluorophosphates, and fluoroethers; optionally, the fluorinated solvent is selected from at least one of fluorocarbonates and fluoroethers. Selecting the above-mentioned fluorinated solvents can further improve the performance of the electrolyte.

[0081] In some embodiments, the fluorocarbonate is selected from at least one of fluoroethylene carbonate (FEC), fluoromethyl ethyl carbonate (FEMC), difluoroethylene carbonate (DFEC), 4-trifluoromethyl ethylene carbonate (TFPC), and di(2,2,2-trifluoroethyl) carbonate (TFEC).

[0082] In some embodiments, the fluorophosphate is selected from at least one of tris(2,2,2-difluoroethyl) phosphate (TFHP) and tris(2,2,2-trifluoroethyl) phosphate (TTFP).

[0083] In some embodiments, the fluoroether is selected from at least one of hydrofluoroether (HFE), 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane (HFEEC), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (F-EPE), methyl nonafluorobutyl ether (MFE), ethyl nonafluorobutyl ether (EFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and nonafluoroisobutyl methyl ether.

[0084] As described above, by selecting fluorinated solvents, it is possible to improve the conductivity and flame retardancy of the electrolyte, as well as at least one of the following properties of the battery containing the electrolyte: energy density, first-cycle specific capacity, first-cycle efficiency, and cycle performance.

[0085] In some embodiments, the electrolyte of this application contains a fluorinated solvent selected from at least one of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether; optionally, the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether; more preferably, the fluorinated solvent is a mixture of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether.

[0086] In some embodiments, the fluorinated solvent is selected from at least one of fluorinated carbonates and fluorinated ethers. In some embodiments, the fluorinated solvent may be selected from: FEC; FEMC; HFE; a mixture of FEC and HFE; or a mixture of FEC, FEMC, and HFE. The inventors have found that, for the electrolyte of this application, the electrolyte obtained using a mixture of fluorinated solvents has better performance than that obtained using a single fluorinated solvent. In some embodiments, the fluorinated solvent may be selected from: FEMC, a mixture of FEC and HFE, or a mixture of FEC, FEMC, and HFE. Optionally, the fluorinated solvent is a mixture of FEC, FEMC, and HFE. Further selection of fluorinated solvents can improve the conductivity, flame retardancy, and at least one of the following properties of the battery containing the electrolyte: energy density, first-cycle specific capacity, first-cycle efficiency, and cycle performance, particularly further improving the flame retardancy and conductivity of the electrolyte.

[0087] In some embodiments, in the electrolyte of this application, when the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether, the content of fluoroethylene carbonate is 10% to 50%, optionally 20% to 40%, based on the total weight of the fluorinated solvent; and / or, the content of hydrofluoroether is 10% to 50%, optionally 20% to 40%; and / or, the content of fluoroethyl methyl carbonate is 0% to 80%, optionally 20% to 60%.

[0088] In some embodiments, in the electrolyte of this application, when the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate and hydrofluoroether, the fluorinated solvent contains at least 10% fluoroethylene carbonate and / or at least 10% hydrofluoroether based on the total weight of the fluorinated solvent.

[0089] Optionally, in some embodiments, the content of the fluoroethylene carbonate is 10% to 50%, optionally 20% to 40%, and more preferably 30% based on the total weight of the fluorinated solvent. In some embodiments, the content of the fluoroethylene carbonate is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% based on the total weight of the fluorinated solvent; or, the content of the fluoroethylene carbonate is within the range of any two of the above values.

[0090] Optionally, in some embodiments, the content of methyl ethyl fluorocarbonate, based on the total weight of the fluorinated solvent, is 0% to 80%, optionally 20% to 60%, and more preferably 40%. In some embodiments, the content of methyl ethyl fluorocarbonate, based on the total weight of the fluorinated solvent, is 0%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%; or, the content of methyl ethyl fluorocarbonate is within the range of any two of the above values.

[0091] Optionally, in some embodiments, the content of the hydrofluoroether is 10% to 50% based on the total weight of the fluorinated solvent, optionally 20% to 40%, and more preferably 30%. In some embodiments, the content of the hydrofluoroether is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% based on the total weight of the fluorinated solvent; or, the content of the hydrofluoroether is within the range of any two of the above values.

[0092] Controlling the content of each component in the fluorinated solvent within the above-mentioned range can further improve the overall performance of the electrolyte.

[0093] In some embodiments, in the electrolyte of this application, when the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether, the weight ratio of fluoroethylene carbonate (FEC), fluoroethyl methyl carbonate (FEMC), and hydrofluoroether (HFE) is (1 to 5):(0 to 8):(1 to 5); optionally, it is (2 to 4):(2 to 6):(2 to 4); more preferably, the weight ratio is 3:4:3. When the fluorinated solvent is a mixture of at least two of FEC, FEMC, and HFE, controlling the content of each component in the mixture within the above-mentioned ratio range can further improve the performance of the electrolyte and the overall performance of the battery containing the electrolyte.

[0094] In this paper, when the weight ratio of a component in a mixture is 0, it means that the mixture does not contain that component. For example, in the weight ratio of FEC, FEMC, and HFE, if the value corresponding to FEMC is 0, it means that the mixture contains only FEC and HFE.

[0095] In this document, " / " means "and"; for example, "FEC / FEMC / HFE" indicates that the fluorinated solvent contains FEC, FEMC, and HFE; that is, the fluorinated solvent is a mixture of FEC, FEMC, and HFE. In describing solvent composition, "FEC / FEMC / HFE (3:4:3)" indicates that the weight ratio of FEC, FEMC, and HFE in the fluorinated solvent mixture is 3:4:3.

[0096] In some embodiments, the lithium halide salt in the electrolyte of this application is selected from at least one of lithium iodide, lithium bromide, lithium chloride, and lithium fluoride; optionally, it is at least one of lithium iodide and lithium bromide. In some embodiments, the lithium halide salt is lithium iodide. By selecting and adding lithium halide salts, the electrolyte of this application has improved conductivity and flame retardancy, thereby improving at least one of the following: energy density, first-cycle specific capacity, first-cycle efficiency, and cycle performance of the lithium-ion battery. Unexpectedly, the addition of the above-mentioned lithium halide salts can effectively suppress dendrite growth, further improving the safety performance of the battery.

[0097] In some embodiments, the fluorosulfonylimide lithium salt in the electrolyte of this application is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), and lithium bis(perfluoro-1-butyryl)imide (LiBPBI); optionally, it is at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. In some embodiments, the fluorosulfonylimide lithium salt is LiFSI. By selecting the electrolyte lithium salt in the electrolyte, the conductivity, flame retardancy, and at least one of the energy density, first-cycle specific capacity, first-cycle efficiency, and cycle performance of the battery containing the electrolyte can be improved. In particular, when the above-mentioned fluorinated solvent is used, selecting the above-mentioned electrolyte salt can significantly improve the conductivity of the electrolyte.

[0098] In some embodiments, the organic solvent in the electrolyte of this application further includes a non-fluorinated organic solvent. In some embodiments, the organic solvent further includes a carbonate solvent; optionally, the carbonate solvent is selected from at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), ethylene carbonate (EC), and propylene carbonate (PC). Optionally, the organic solvent includes EMC. The inclusion of the above solvents in the electrolyte can dissolve and dissociate lithium salts and improve lithium-ion mobility.

[0099] In some embodiments, the electrolyte of this application further includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium perchlorate (LiClO4). In some embodiments, the electrolyte salt is optionally LiPF6. By further including the above-mentioned electrolyte lithium salt, the cost can be reduced and the conductivity of the electrolyte can be improved, thereby improving the overall performance of the electrolyte.

[0100] In some embodiments, the electrolyte of this application further comprises other functional additives, which may be any additives applicable in the context of this application and known in the art. In some embodiments, the electrolyte of this application further comprises at least one of film-forming additives, flame-retardant additives, overcharge prevention additives, and conductive additives. The inclusion of the above-mentioned additives in the electrolyte can further improve the performance of the electrolyte.

[0101] Although the mechanism is unclear, the inventors have discovered that there is a "synergistic effect" among the fluorinated solvent, electrolyte lithium salt and halide lithium salt contained in the electrolyte of this application, which can effectively suppress the unwanted lithium dendrite growth in lithium-ion secondary batteries, thereby further improving the safety performance of lithium-ion secondary batteries.

[0102] In some embodiments, the electrolyte of this application is a high-voltage electrolyte.

[0103] In some embodiments, the electrolyte of this application is used in lithium-ion batteries with non-lithium metal anodes. Optionally, the electrolyte of this application is used in lithium-ion batteries with graphite anodes.

[0104] By using the electrolyte of this application, lithium-ion secondary batteries with graphite anodes can significantly suppress lithium dendrite growth at higher operating voltages (e.g., above 4.2V) and exhibit good overall performance.

[0105] Secondary batteries, battery modules, battery packs and electrical devices

[0106] The secondary battery, battery module, battery pack, and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0107] In one embodiment of this application, a secondary battery is provided.

[0108] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0109] In some embodiments, the secondary battery is a lithium-ion secondary battery.

[0110] [Positive electrode plate]

[0111] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0112] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0113] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0115] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0116] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0117] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0118] [Negative electrode plate]

[0119] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0120] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0121] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0123] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0124] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0126] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0127] [Isolation membrane]

[0128] In some embodiments, the secondary battery also includes a separator. 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.

[0129] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0130] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0131] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0132] 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; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0133] 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. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0134] In some implementations, refer to Figure 2 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 forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0135] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0136] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 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.

[0137] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0138] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0139] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0140] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided 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 may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0141] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0142] Figure 6This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0143] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0144] Example

[0145] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0146] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments used in the examples, unless otherwise specified, are all commercially available conventional products.

[0147] Preparation method

[0148] The electrolyte of this application and the secondary battery containing the electrolyte were prepared according to the component contents shown in Table 1 and the following steps. The electrolyte and the corresponding lithium-ion battery in the comparative examples were also prepared in the same manner.

[0149] 1. Electrolyte preparation

[0150] The electrolyte was prepared in a drying chamber at a temperature of 23±1℃ according to Table 1 below. First, the solvent components (such as fluorinated solvents and / or non-fluorinated solvents) were mixed according to Table 1 to prepare an organic solvent. Then, the appropriate amounts of electrolyte lithium salt and lithium halide salt were added to the organic solvent and mixed evenly by conventional methods to obtain the electrolyte of this application.

[0151] 2. Preparation of positive electrode sheet

[0152] The positive electrode active material lithium nickel cobalt manganese oxide (NCM) 523 The following ingredients were mixed: PVDF (polyvinylidene fluoride) binder, and acetylene black (acetylene black) conductive agent, at a mass ratio of 98:1:1. The resulting mixture was then added to the organic solvent N-methylpyrrolidone (NMP) until the system became homogeneous and transparent (solid content 73%). The mixture was then stirred in a vacuum mixer to obtain the positive electrode active material slurry. The positive electrode active material slurry was then subjected to a concentration of 20 mg / cm³. 2 The load is uniformly coated on the current collector aluminum foil and dried at 85°C. Then, it is cold-pressed and cut into strip rolls (width 31±0.5mm) to obtain the positive electrode sheet.

[0153] 3. Preparation of negative electrode sheet

[0154] A negative electrode active material slurry (solid content 52%) was prepared by mixing graphite, conductive agent Super P, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) with deionized water at a mass ratio of 97:1:1:1. The slurry was then subjected to a concentration of 11.5 g / cm³. 2 The load is evenly coated on the current collector copper foil and dried at 85℃. After drying, it is cold-pressed and cut into strip rolls (width 32±0.5mm) to obtain the negative electrode sheet.

[0155] 4. Lithium-ion battery manufacturing

[0156] Polypropylene film cut into strips (width 33.5±0.5mm) is used as the separator. The prepared positive electrode, separator, and negative electrode are aligned and stacked in the order of "positive electrode - separator - negative electrode", with the separator in the middle of the positive and negative electrode and tightly attached to the positive and negative electrode respectively (electrode tension 120±5g, separator tension 110±5g). Then, it is wound to obtain a bare cell. The bare cell is placed in the battery outer packaging, and then 28±0.5g of electrolyte is injected. After encapsulation, standing, formation, shaping, and capacity testing, a lithium-ion secondary battery is prepared.

[0157] Electrolyte performance testing methods

[0158] 1. Electrolyte conductivity measurement

[0159] The electrolyte sample to be tested was placed in a platinum black conductivity cell (Fangzhou FZ-705W) in a glove box and sealed. Then, the impedance curve was measured using the alternating impedance (EIS) method (Solartron 1260 / 1287, test conditions: amplitude 2-10mV, frequency starting from 0.1Hz and continuing to 100000-200000Hz), and the electrolyte conductivity was calculated.

[0160] 2. Evaluation of electrolyte combustion performance

[0161] The self-extinguishing time (SET) method was used to evaluate the flammability of the electrolyte. The specific steps involved preparing glass wool balls with a diameter of approximately 3 mm to 5 mm from fiberglass wool and placing them on a wire mesh. Using a syringe, samples of the electrolyte to be tested (each sample had a different electrolyte composition) were injected into the glass wool balls. Immediately after injection, the balls were ignited (within 2 seconds). The time interval between the removal of the ignition device and the automatic extinguishing of the flame was recorded; this time interval was called the self-extinguishing time. The difference in mass of the syringe before and after injection was measured and recorded as the mass of the injected electrolyte. Then, the self-extinguishing time per unit mass of electrolyte was calculated, and this time was used to evaluate the flame-retardant performance of each electrolyte sample: the shorter the self-extinguishing time per unit mass of electrolyte, the better the flame-retardant performance.

[0162] 3. First-week discharge specific capacity and first-week efficiency test of lithium-ion secondary batteries

[0163] The prepared lithium-ion secondary battery was tested at 25°C with a current of 1.5 mA / cm². 2 It is charged with a constant current to 4.25V, and then charged with a constant voltage of 4.25V until the current drops to 0.3 mA / cm². 2 The first-week charging specific capacity (Cc1) was obtained; then, at 1.5 mA / cm², the specific capacity was calculated. 2 Discharge the lithium-ion battery to 3.0V with a constant current to obtain the first-cycle discharge specific capacity (Cd1), and calculate the first-cycle efficiency of the lithium-ion battery according to the following formula.

[0164] First-week efficiency of lithium-ion battery = First-week discharge specific capacity (Cd1) / First-week charge specific capacity (Cc1)

[0165] 4. Lithium-ion battery energy density test

[0166] The prepared lithium-ion battery was tested at 25°C with a current of 1.5 mA / cm². 2 It is charged with a constant current to 4.25V, and then charged with a constant voltage of 4.25V until the current drops to 0.3 mA / cm². 2 Then at 1.5 mA / cm 2 The lithium-ion battery is discharged to 3.0V under constant current, the energy of the lithium-ion battery is measured, and the energy density of the lithium-ion battery is calculated according to the following formula.

[0167] Energy density (Wh / kg) = Battery energy / Battery mass

[0168] 5. Lithium-ion battery capacity retention test

[0169] The lithium-ion battery was subjected to a speed of 1.5 mA / cm at 25°C. 2 It is charged with a constant current to 4.25V, and then charged with a constant voltage of 4.25V until the current drops to 0.3 mA / cm².2 Then at 1.5 mA / cm 2 Discharge the battery with a constant current to 3.0V to obtain the initial discharge specific capacity (Cd1); repeat this charge-discharge cycle until the nth cycle to obtain the discharge specific capacity after n cycles, denoted as Cdn, and calculate the capacity retention rate of the lithium-ion battery according to the following formula:

[0170] Capacity retention rate = discharge specific capacity after n cycles (Cdn) / discharge specific capacity in the first cycle (Cd1).

[0171] 6. Test to suppress lithium dendrite growth – Observation of the surface of the negative electrode sheet

[0172] The lithium-ion battery that has undergone 100 cycles was disassembled, and the surface morphology of the negative electrode was observed using an optical microscope to determine whether lithium dendrites were formed.

[0173] The specific test data for each embodiment and comparative example are shown in Table 1 below.

[0174] It should be noted that in Table 1 below, t = [(k*a*c) / (k*a+c)] / b, where k, a, b, and c are as defined above. The original value calculated according to the above formula is obtained by discarding the next digit and retaining three significant figures, thus obtaining the value of t.

[0175] Table 1

[0176]

[0177] The embodiments and comparative examples of this application demonstrate that the electrolyte of this application, by containing fluorinated solvents, fluorinated electrolyte salts, and lithium halide salts, exhibits good conductivity and achieves excellent safety performance at higher operating voltages, such as improved flame retardancy and significant inhibition of lithium dendrite growth, thereby enhancing battery safety performance. Furthermore, the electrolyte of this application can improve the energy density, output performance, and cycle performance of lithium-ion secondary batteries.

[0178] In particular, the electrolyte of this application can effectively improve the first-cycle efficiency of the battery—the first-cycle efficiency of the lithium-ion battery with the electrolyte of this application is above 85%, which reduces the initial irreversible capacity loss of the battery and further improves the energy density.

[0179] Furthermore, a comparison of the above embodiments and comparative data reveals a synergistic effect among the fluorinated solvent, fluorinated electrolyte salt, and lithium halide salt in the electrolyte of this application. This synergistic effect effectively suppresses lithium dendrite growth in lithium-ion secondary batteries using graphite as the negative electrode. As shown in the table above, using the electrolyte of this application significantly suppresses lithium dendrite growth after 200 cycles in lithium-ion batteries. This indicates that the electrolyte of this application is beneficial for improving the interfacial composition and lithium deposition morphology on the negative electrode surface, effectively suppressing lithium dendrite growth during battery cycling and improving cycle performance.

[0180] In summary, the electrolyte of this application can suppress lithium dendrite growth in lithium-ion batteries, improve lithium plating, improve battery cycle performance, improve flame retardancy, and improve battery energy density, effectively solving the defects existing in the prior art.

[0181] 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.

[0182] [1] In Examples 23 to 28, the percentages are weight percentages based on the total weight of the organic solvents.

[0183] [2] In Examples 39-47, the percentages in this column are molar percentages based on the total molar amount of the electrolyte lithium salt.

Claims

1. An electrolyte comprising an organic solvent, a lithium electrolyte salt, and additives; in, The organic solvent includes fluorinated solvents; The electrolyte lithium salt includes a fluorinated sulfonyl imide lithium salt; The additives include lithium halide salts; The fluorinated solvent is selected from one of the following: (i) Selected from at least two combinations of fluoroethylene carbonate, fluoromethyl ethyl carbonate, 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and nonafluoroisobutyl methyl ether; (ii) Ethyl fluorocarbonate; (iii) Fluoroethylene carbonate; (iv) A hydrofluoroether selected from at least one of the following: 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and nonafluoroisobutyl methyl ether; (v) A combination of methyl ethyl carbonate and a hydrofluoroether selected from at least one of the following: fluoroethylene carbonate, fluoromethyl ethyl carbonate, 3-(2,2,3,3-tetrafluoropropoxy)-1,2-epoxypropane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, nonafluoroisobutyl methyl ether; The following relationship exists between the fluorinated sulfonyl imide lithium salt, the lithium halide salt, and the fluorinated solvent: t = [(k*a*c) / (k*a+c)] / b, and the value of t is in the range of 0.0004 to 0.1000. in, k is the molar concentration of the electrolyte lithium salt, in mol / L. a is the molar percentage of fluorosulfonylimide lithium salt based on the total molar amount of the electrolyte lithium salt. b is the weight percentage of fluorinated solvents based on the total weight of organic solvents. c is the weight percentage of lithium halide salts based on the total weight of the electrolyte. a, b, c, and k are all non-zero; Based on the total weight of the organic solvents, the content of the fluorinated solvent is 20% by weight or more; The molar concentration of the electrolyte lithium salt is from 0.5 mol / L to 8 mol / L; Based on the total weight of the electrolyte, the content of the lithium halide salt is from 0.5% to 10% by weight.

2. The electrolyte according to claim 1, wherein, The value of t is in the range of 0.0190 to 0.0400.

3. The electrolyte according to claim 1, wherein, The content of the fluorinated solvent is 50% by weight or more, based on the total weight of the organic solvent.

4. The electrolyte according to claim 3, wherein, The content of the fluorinated solvent is 80% by weight or more, based on the total weight of the organic solvent.

5. The electrolyte according to claim 1, wherein, The molar concentration of the electrolyte lithium salt is from 1.5 mol / L to 4 mol / L.

6. The electrolyte according to claim 1, wherein, Based on the total weight of the electrolyte, the content of the lithium halide salt is from 0.5% to 7% by weight.

7. The electrolyte according to claim 6, wherein, Based on the total weight of the electrolyte, the content of the lithium halide salt is from 1% to 6% by weight.

8. The electrolyte according to claim 1, wherein, Based on the total molar amount of the electrolyte lithium salt, the molar percentage of the fluorosulfonylimide lithium salt is at least 30%.

9. The electrolyte according to claim 8, wherein, Based on the total molar amount of the electrolyte lithium salt, the molar percentage of the fluorosulfonamide lithium salt is at least 60%.

10. The electrolyte according to claim 9, wherein, Based on the total molar amount of the electrolyte lithium salt, the molar percentage of the fluorosulfonamide lithium salt is at least 90%.

11. The electrolyte according to claim 1, wherein, When the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether, Based on the total weight of the fluorinated solvent, the content of the fluoroethylene carbonate is 10% to 50%; and / or, the content of the hydrofluoroether is 10% to 50%; and / or, the content of the fluoroethyl methyl carbonate is 0% to 80%.

12. The electrolyte according to claim 11, wherein, When the fluorinated solvent is a mixture of at least two of fluoroethylene carbonate, fluoroethyl methyl carbonate, and hydrofluoroether, Based on the total weight of the fluorinated solvent, the content of the fluoroethylene carbonate is 20% to 40%; and / or, the content of the hydrofluoroether is 20% to 40%; and / or, the content of the fluoroethyl methyl carbonate is 20% to 60%.

13. The electrolyte according to claim 1, wherein the lithium halide salt is selected from at least one of lithium iodide, lithium bromide, lithium chloride and lithium fluoride.

14. The electrolyte according to claim 13, wherein, The lithium halide salt is at least one of lithium iodide and lithium bromide.

15. The electrolyte according to claim 1, wherein, The fluorinated sulfonyl imide lithium salt is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide, and lithium bis(perfluoro-1-butyryl)imide.

16. The electrolyte according to claim 15, wherein, The fluorosulfonylimide lithium salt is at least one of lithium bis(fluorosulfonylimide) and lithium bis(trifluoromethanesulfonyl)imide.

17. The electrolyte according to claim 1, wherein, The electrolyte lithium salt also includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, and lithium perchlorate.

18. The electrolyte according to claim 1, wherein, The electrolyte also includes at least one of film-forming additives, flame-retardant additives, overcharge prevention additives, and conductive additives.

19. A secondary battery comprising the electrolyte according to any one of claims 1 to 18.

20. A battery module comprising the secondary battery of claim 19.

21. A battery pack comprising the battery module of claim 20.

22. An electrical device comprising at least one selected from the secondary battery of claim 19, the battery module of claim 20, or the battery pack of claim 21.

Images