Lithium metal battery, method of making the same, and electric device

Abstract

The application provides a lithium metal battery, a preparation method thereof and an electric device. The lithium metal battery comprises a negative electrode sheet, a positive electrode sheet and an electrolyte; the negative electrode sheet comprises lithium metal; the electrolyte comprises a lithium salt, a long-chain fluorinated ether solvent A and a short-chain fluorinated ether solvent B; the structures of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B are shown in formula I and formula II respectively: R1 comprises F, C1-C3 alkyl or fluorinated C1-C3 alkyl, R'1 comprises H, C1-C3 alkyl or fluorinated C1-C3 alkyl; R2 and R3 each independently comprise C1-C3 alkyl or fluorinated C1-C3 alkyl, R4 and R7 each independently comprise F or fluorinated C1-C3 alkyl; R5 to R9 each independently comprise H or F. Thus, by regulating the composition of the electrolyte, the large-particle-size densification lithium deposition can be promoted, the irreversible expansion of the battery during the cycle process can be relieved or inhibited, and the cycle performance can be improved.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a lithium metal battery, its preparation method, and an electrical device thereof. Background Technology

[0002] In recent years, the application range of rechargeable batteries has become increasingly wide, with applications in energy storage power 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. Among them, lithium metal batteries are highly favored due to their high energy density and safer manufacturing process. However, traditional lithium metal batteries currently suffer from severe irreversible cell expansion during cycling, which reduces the battery's cycle performance. Summary of the Invention

[0003] Based on this, this application provides a lithium metal battery with improved cycle performance, a method for preparing the same, and an electrical device thereof.

[0004] The first aspect of this application provides a lithium metal battery, comprising a negative electrode, a positive electrode, and an electrolyte; the negative electrode comprises lithium metal, and the electrolyte comprises a lithium salt, a long-chain fluorinated ether solvent A, and a short-chain fluorinated ether solvent B, wherein the structures of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B are shown in Formula I and Formula II, respectively:

[0005] , ;

[0006] R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R'1 includes H, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R2 and R3 each independently include C1-C3 alkyl or fluorinated C1-C3 alkyl; R4 and R7 each independently include F or fluorinated C1-C3 alkyl; R5, R6, R8, and R9 each independently include H or F.

[0007] The aforementioned lithium metal battery optimizes the molecular structure of the solvent in the electrolyte by using a combination of two solvents: long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B. Long-chain fluorinated ether solvent A has multiple ether oxygen bonds, and R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl groups. It can dissolve lithium salts and has a weak solvation effect on lithium ions, weakening the interaction between solvent molecules and lithium ions. This promotes the participation of anions in the lithium salt in solvation and decomposition to form a more inorganic SEI. Short-chain fluorinated ether solvent B does not participate in solvation; it acts as a diluent. Its small molecular size can reduce... The low viscosity of the electrolyte improves the lithium-ion transport kinetics of lithium metal batteries. In addition, both long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B have good thermodynamic compatibility with lithium metal, reducing side reactions between the electrolyte and lithium metal. This promotes the formation of a more inorganic SEI film on the negative electrode, which has better lithium-ion transport performance. This, in turn, promotes the deposition of large-particle-size, dense lithium, thereby reducing the generation and continuous accumulation of inactive lithium, alleviating or inhibiting irreversible expansion of the cell during cycling, and improving cycle performance.

[0008] In some implementations, R'1 is H; and / or,

[0009] The total number of fluorine atoms in R1, R2, and R3 is ≤6; optionally, R2 and R3 each independently include a C1-C3 alkyl group, more preferably, R2 and R3 each independently include a methyl or ethyl group; and / or,

[0010] The number of fluorine atoms in the fluorinated C1-C3 alkyl group of R1 is ≥2; optionally, R1 includes trifluoromethyl.

[0011] Only R1 is substituted in R1 and R'1, which allows for appropriate control of the steric hindrance of the long-chain fluoroether solvent A, while also providing moderate solvation, which is beneficial for dissolving lithium salts.

[0012] By controlling the total number of fluorine atoms, the steric hindrance of the long-chain fluorinated ether solvent A can be reduced, and the degree of fluorination can be moderate, which is beneficial for dissolving lithium salts.

[0013] The increased number of fluorine atoms in fluorinated C1-C3 alkyl groups significantly enhances electron-withdrawing properties. When applied to electrolytes, this can induce the formation of a more inorganic-rich SEI, which in turn promotes the deposition of large-particle-size, dense lithium. This reduces the generation and continuous accumulation of inactive lithium, alleviates or inhibits irreversible expansion of the cell during cycling, and improves cycle performance.

[0014] In some embodiments, the long-chain fluorinated ether solvent A comprises one or more compounds of formulas I-1 to I-4:

[0015] .

[0016] These long-chain fluorinated ether solvents A have a moderate chain length and degree of fluorination, balancing high chemical stability and lithium salt solubility.

[0017] In some embodiments, R4 and R7 each independently comprise a fluoromethyl or a fluoroethyl; and / or, the total number of fluorine atoms in R4 and R7 is ≥4;

[0018] Optionally, the number of fluorine atoms in both R4 and R7 is ≥2;

[0019] Alternatively, R4 and R7 may each independently include a difluoromethyl or a trifluoromethyl group.

[0020] In short-chain fluorinated ether solvent B, a higher total number of fluorine atoms in R4 and R7 indicates a higher degree of fluorination. Controlling the total number of fluorine atoms in R4 and R7 within this range provides a moderate degree of fluorination, ensuring that short-chain fluorinated ether solvent B does not react with Li... + Direct coordination allows for control over its low molecular weight, improving the efficiency of Li. + The better the diffusion kinetics, the better the cycle performance of the battery.

[0021] In some embodiments, the short-chain fluoroether solvent B comprises one or more compounds of formulas II-1 to II-6:

[0022] .

[0023] In some embodiments, the volume ratio b of the long-chain fluorinated ether solvent A to the short-chain fluorinated ether solvent B is 0.2 to 5; optionally, the volume ratio b is 0.4 to 2.5.

[0024] The primary function of long-chain fluorinated ether solvent A is as a solvent for lithium salts. However, its viscosity is higher than that of short-chain fluorinated ether solvent B. Higher viscosity affects the wettability of the electrolyte. The addition of short-chain fluorinated ether solvent B can act as a diluent, thereby reducing the viscosity of the electrolyte. However, it reduces the solubility of lithium salts, affecting lithium-ion transport performance. Therefore, controlling the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B within the aforementioned ratio can balance electrolyte wettability and lithium-ion transport performance. Furthermore, the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B is also related to the concentration of lithium salts. Higher lithium salt concentrations require a larger volume of long-chain fluorinated ether solvent A to dissolve the lithium salt, i.e., a larger volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B, to optimize the solubility of lithium salts and lithium-ion transport performance.

[0025] In some embodiments, the total volume percentage of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B in the solvent of the electrolyte is 90% to 100%.

[0026] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 5 mol / L, and optionally 1 mol / L to 3 mol / L.

[0027] In some embodiments, the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, lithium nitrate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0028] In some embodiments, the negative electrode sheet further includes a negative current collector and a lithium metal particle layer disposed on the negative current collector. The lithium metal particle layer includes lithium metal particles with an average particle size of 20 μm to 100 μm, optionally 30 μm to 90 μm.

[0029] In traditional lithium metal batteries, the average particle size of deposited lithium particles is usually below 10 μm. The lithium metal battery described in this application promotes the deposition of large-particle-size dense lithium by adjusting the electrolyte composition, so that the average particle size of the deposited lithium metal particles is in the range of 20 μm to 100 μm. This promotes the deposition of large-particle-size dense lithium, thereby reducing the generation and continuous accumulation of inactive lithium, alleviating or suppressing the irreversible expansion of the cell during cycling, and improving cycle performance.

[0030] In some embodiments, the negative electrode sheet further includes a lithium foil layer located between the negative electrode current collector and the lithium metal particle layer;

[0031] Optionally, the thickness of the lithium foil layer is 5μm to 50μm.

[0032] In some embodiments, the operating temperature of the lithium metal battery is 30°C to 80°C; optionally, it is 40°C to 70°C. Appropriately increasing the charging temperature reduces mass transfer and reaction polarization, further increasing the particle size distribution of lithium deposition. Based on improvements in electrolyte composition combined with temperature optimization, these two improvements work together to achieve large-particle-size, dense lithium deposition, significantly reducing the generation and continuous accumulation of inactive lithium, suppressing irreversible expansion of the cell, and achieving zero or low irreversible expansion.

[0033] In some embodiments, the rated charging current of the lithium metal battery is 0.1 mA / cm². 2 ~1mA / cm 2 At this lower charging current, it can also increase the lithium deposition particle size of the lithium metal particle layer.

[0034] In some embodiments, the positive electrode sheet includes a positive electrode active material, which includes one or more of olivine-structured lithium phosphates, lithium transition metal oxides, and their respective modified compounds.

[0035] A second aspect of this application provides a method for preparing a lithium metal battery, comprising the following steps:

[0036] A lithium metal battery is prepared by injecting an electrolyte into an electrode assembly.

[0037] The electrode assembly includes a negative electrode and a positive electrode. The negative electrode includes lithium metal. The electrolyte includes a lithium salt, a long-chain fluorinated ether solvent A, and a short-chain fluorinated ether solvent B. The structures of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B are shown in Formula I and Formula II, respectively.

[0038] , ;

[0039] R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R'1 includes H, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R2 and R3 each independently include C1-C3 alkyl or fluorinated C1-C3 alkyl; R4 and R7 each independently include F or fluorinated C1-C3 alkyl; R5, R6, R8, and R9 each independently include H or F.

[0040] In some embodiments, the lithium metal battery prepared by the method is the lithium metal battery provided in the first aspect of this application.

[0041] In a third aspect, this application provides an electrical device, including at least one of the lithium metal battery provided in the first aspect of this application and the lithium metal battery prepared by the preparation method provided in the second aspect of this application.

[0042] The electrical device of this application includes the lithium metal battery provided in this application, and therefore has at least the same advantages as the lithium metal battery.

[0043] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0044] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0045] Figure 1 This is a schematic diagram of a lithium metal battery according to one embodiment of this application.

[0046] Figure 2 yes Figure 1 An exploded view of a lithium metal battery according to an embodiment of this application is shown.

[0047] Figure 3 This is a schematic diagram of a battery device according to one embodiment of this application.

[0048] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0049] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0050] Figure 6 This is a schematic diagram of an electrical device using a lithium metal battery as a power source according to an embodiment of this application.

[0051] Figure 7 This is a SEM image of the lithium metal particle layer surface of the negative electrode in the lithium metal battery cell of Comparative Example 5 and Example 1.

[0052] Figure 8 These are monitoring curves of the cell thickness of lithium metal battery cells in Comparative Example 5 and Example 1 as a function of cycle time.

[0053] Explanation of reference numerals in the attached figures:

[0054] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery assembly; 5. Individual battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0055] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0056] The "range" disclosed in this application can be defined in the form of 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; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning 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 ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also 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 document; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2-10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0057] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0060] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0061] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0062] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0063] Lithium metal batteries are favored for their high energy density and safer manufacturing process. However, traditional lithium metal batteries currently suffer from severe irreversible cell expansion during cycling.

[0064] This study found that the irreversible expansion of lithium metal batteries mainly originates from the continuous accumulation of inactive lithium on the negative electrode side, and the generation of inactive lithium is closely related to the deposition morphology of lithium. The smaller the lithium particle size deposited on the negative electrode side, the easier it is to generate a large amount of inactive lithium during cycling, which then accumulates on the electrode surface, causing the cell to expand continuously and irreversibly.

[0065] Based on this, this application targets lithium metal batteries and induces the formation of a more inorganic SEI film on the negative electrode by adjusting the electrolyte composition. The more inorganic SEI film has better lithium-ion transport performance, which can promote the deposition of large-particle-size dense lithium. This reduces the generation and continuous accumulation of inactive lithium, alleviates or inhibits the irreversible expansion of the cell during cycling, and improves cycle performance.

[0066] One embodiment of this application provides a lithium metal battery, including a negative electrode, a positive electrode, and an electrolyte. The negative electrode includes lithium metal, and the electrolyte includes a lithium salt, a long-chain fluorinated ether solvent A, and a short-chain fluorinated ether solvent B.

[0067] The structures of long-chain fluorinated ether solvent A and chain fluorinated ether solvent B are shown in Formula I and Formula II, respectively:

[0068] , ;

[0069] R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R'1 includes H, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R2 and R3 each independently include C1-C3 alkyl or fluorinated C1-C3 alkyl; R4 and R7 each independently include F or fluorinated C1-C3 alkyl; R5, R6, R8, and R9 each independently include H or F.

[0070] The aforementioned lithium metal battery optimizes the molecular structure of the solvent in the electrolyte by using a combination of two solvents: a long-chain fluorinated ether solvent A and a short-chain fluorinated ether solvent B. Long-chain fluorinated ether solvent A has multiple ether oxygen bonds, and R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl groups. It can dissolve lithium salts and has a weak solvation effect on lithium ions, weakening the interaction between solvent molecules and lithium ions, promoting the participation of anions in solvation and decomposition to form a more inorganic SEI. Short-chain fluorinated ether solvent B does not participate in solvation; it acts as a diluent. Its small molecular size allows for... Reducing the viscosity of the electrolyte improves the lithium-ion transport kinetics of lithium metal batteries. Furthermore, both long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B exhibit good thermodynamic compatibility with lithium metal, reducing side reactions between the electrolyte and lithium metal. This promotes the formation of a more inorganic-rich SEI film at the negative electrode, which in turn exhibits better lithium-ion transport performance. This, in turn, facilitates the deposition of large-particle-size, dense lithium, thereby reducing the generation and continuous accumulation of inactive lithium, mitigating or suppressing irreversible expansion of the cell during cycling, and improving cycle performance.

[0071] Understandably, "C1-C3 alkyl" refers to methyl, ethyl, or propyl. "Fluorinated C1-C3 alkyl" refers to fluoromethyl, fluoroethyl, or fluoropropyl. "Fluorinated C1-C3 alkyl" refers to any one or more H groups in the C1-C3 alkyl group that are substituted with F; other fluoroalkyl groups have similar meanings.

[0072] In some embodiments, R1 is F, a C1-C3 alkyl, or a fluorinated C1-C3 alkyl. In some embodiments, R'1 is H, a C1-C3 alkyl, or a fluorinated C1-C3 alkyl. In some embodiments, R2 and R3 are each independently a C1-C3 alkyl or a fluorinated C1-C3 alkyl.

[0073] In some embodiments, R'1 is H. Only R1 is substituted among R1 and R'1, which allows for appropriate steric hindrance of the long-chain fluoroether solvent A, while also providing moderate solvation, which is beneficial for dissolving lithium salts.

[0074] In some embodiments, the total number of fluorine atoms in R1, R2, and R3 is ≤6; for example, it can be 0, 1, 2, 3, 4, 5, or 6. Controlling the total number of fluorine atoms allows for less steric hindrance in the long-chain fluorinated ether solvent A, resulting in a moderate degree of fluorination, which is beneficial for dissolving lithium salts.

[0075] Further, R2 and R3 each independently comprise a C1-C3 alkyl group, and more preferably, R2 and R3 each independently comprise a methyl or ethyl group. Further, R2 and R3 are methyl or ethyl. Optionally, at least one of R2 and R3 comprises an ethyl group, resulting in better cycle performance and lower cell expansion rate of the battery.

[0076] In this application, fluoromethyl groups include, but are not limited to, monofluoromethyl, difluoromethyl, or trifluoromethyl groups.

[0077] As an example, the number of fluorine atoms in the fluorinated C1-C3 alkyl group of R1 can be 1, 2, 3, 4, 5, or 6. Furthermore, if R1 is a fluorinated C1-C3 alkyl group, increasing the degree of fluorination weakens the electron cloud density of oxygen atoms, creating a weakly solvated environment and inducing the formation of a more inorganic SEI. If R1 is F, it is speculated that while the fluorine group has electron-withdrawing ability, it also has some electron-donating effect, though less effective than the fluorinated C1-C3 alkyl group. Moreover, as the number of fluorine atoms in the fluorinated C1-C3 alkyl group increases, the electron-withdrawing effect significantly strengthens. Therefore, when applied to the electrolyte, it can induce the formation of a more inorganic SEI, thereby promoting the deposition of large-particle-size, dense lithium. This reduces the generation and continuous accumulation of inactive lithium, alleviates or inhibits irreversible expansion of the cell during cycling, and improves cycle performance.

[0078] In some embodiments, the number of fluorine atoms in the fluorinated C1-C3 alkyl group of R1 is ≥2; optionally, R1 includes a trifluoromethyl group.

[0079] As an example, long-chain fluoroether solvent A includes one or more compounds of formulas I-1 to I-4:

[0080]

[0081] These long-chain fluorinated ether solvents A have a moderate chain length and degree of fluorination, balancing high chemical stability and lithium salt solubility.

[0082] In some embodiments, R4 and R7 are each independently F or fluorinated C1-C3 alkyl. In some embodiments, R5, R6, R8, and R9 are each independently H or F.

[0083] In some embodiments, R4 and R7 each independently comprise a fluorinated C1-C3 alkyl group, such as a fluorinated methyl or a fluorinated ethyl group.

[0084] As an example, in structural formula II of short-chain fluorinated ether solvent B, the total number of fluorine atoms in R4 and R7 can be any value from 1, 2, 3, 4, 5, 6, 7, 8, 9, to 10. Optionally, the total number of fluorine atoms in R4 and R7 is ≥4, and further optionally 4 to 6. The higher the total number of fluorine atoms in R4 and R7 of short-chain fluorinated ether solvent B, the higher its degree of fluorination. Controlling the total number of fluorine atoms in R4 and R7 within this range allows for moderate control of the degree of fluorination, ensuring that short-chain fluorinated ether solvent B does not react with Li. + Direct coordination allows for control over its low molecular weight, improving the efficiency of Li. + The better the diffusion kinetics, the better the cycle performance of the battery.

[0085] As an example, the number of fluorine atoms in R4 and R7 can be any value from 1, 2, 3, 4, 5, 6, 7, 8, 9, to 10. Optionally, the number of fluorine atoms in R4 and R7 can both be ≥2, and can further be 2 to 3. The better the dispersion of fluorine atoms in R4 and R7, the weaker the interaction between the short-chain fluorinated ether solvent B and lithium ions, the more it helps to act as a diluent, and therefore the better the cycle performance of the battery.

[0086] Alternatively, R4 and R7 may each independently include a difluoromethyl or a trifluoromethyl group.

[0087] In some examples, R5 and R6 are hydrogen atoms. In some examples, R8 and R9 are hydrogen atoms. In some examples, R5, R6, R8, and R9 are hydrogen atoms. In some examples, some of R5, R6, R8, and R9 are fluorine atoms and some are hydrogen atoms.

[0088] As an example, short-chain fluoroether solvent B includes one or more compounds of formulas II-1 to II-6:

[0089] .

[0090] In some embodiments, the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B is 0.2~5. Long-chain fluorinated ether solvent A primarily functions as a solvent for the lithium salt, but its viscosity is higher than that of short-chain fluorinated ether solvent B. Higher viscosity affects the wettability of the electrolyte. The addition of short-chain fluorinated ether solvent B can act as a diluent, thereby reducing the viscosity of the electrolyte. However, it reduces the solubility of the lithium salt, affecting lithium-ion transport performance. Therefore, controlling the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B within the aforementioned ratio balances electrolyte wettability and lithium-ion transport performance. Furthermore, the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B is also related to the concentration of the lithium salt. A higher lithium salt concentration requires a larger volume of long-chain fluorinated ether solvent A to dissolve the lithium salt, i.e., a larger volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B, to optimize the solubility of the lithium salt and lithium-ion transport performance.

[0091] As an example, the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B can be 0.2, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.5, 2.6, 2.8, 3, 3.2, 3.4, 3.5, 3.6, 3.8, 4, 4.2, 4.4, 4.5, 4.6, 4.8, 5, or any two of the above values; optionally, the volume ratio b is 0.2 to 2.5; further, 0.4 to 2.5; even further, 0.4 to 1.5, 0.5 to 2, or 0.8 to 1.5. Furthermore, controlling the volume ratio b of long-chain fluorinated ether solvent A to short-chain fluorinated ether solvent B within the above range can balance the lithium-ion transport performance of the lithium salt and the wettability of the electrolyte, improving the stability of lithium deposition.

[0092] In some embodiments, the total volume percentage of long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B in the electrolyte solvent is 90% to 100%. For example, this total volume percentage is 90%, 92%, 95%, 98%, 100%, or any two of the above values. That is, the electrolyte solvent can be composed of long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B. Furthermore, in addition to the above volume percentages, other solvents, such as other ether solvents, may also be included.

[0093] In some of these embodiments, the electrolyte has a viscosity of 2 mPa s to 10 mPa s at 25°C.

[0094] In some embodiments, the concentration of lithium salt in the electrolyte is 0.5 mol / L to 5 mol / L, and can be selected as 1 mol / L to 3 mol / L.

[0095] As an example, the concentration of lithium salt is 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L, 5.0 mol / L, or any two of the above values.

[0096] In some embodiments, the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiOTF), lithium difluorophosphate (LiDFP), lithium dioxolaneborate (LiBOB), lithium difluorooxolaneborate (LiDFOB), lithium nitrate (LiNO3), lithium difluorodioxolane phosphate, and lithium tetrafluorooxolane phosphate.

[0097] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0098] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0099] In some embodiments, the negative electrode further includes a negative current collector and a lithium metal particle layer disposed on the negative current collector. The lithium metal particle layer comprises lithium metal particles with an average particle size of 20 μm to 100 μm, optionally 30 μm to 90 μm. Conventional lithium metal batteries typically deposit lithium particles with an average particle size below 10 μm. The lithium metal battery described in this application promotes the deposition of large-particle-size, dense lithium by controlling the electrolyte composition, resulting in deposited lithium metal particles with an average particle size in the range of 20 μm to 100 μm. This promotes the deposition of large-particle-size, dense lithium, thereby reducing the generation and continuous accumulation of inactive lithium, alleviating or suppressing irreversible expansion of the cell during cycling, and improving cycle performance.

[0100] The average particle size test method for lithium metal particles is as follows: Disassemble the battery to obtain the negative electrode sheet, cut a 6mm×6mm negative electrode sheet sample, and perform scanning electron microscopy on the lithium metal particle layer on the surface of the negative electrode sheet. Select five regions with the same area and containing 10-20 particles at five positions (four corners and center) under the scanning electron microscope, and count the particle size of the particles in them. Take the shortest diagonal dimension as the particle size, and obtain the average particle size of the particles in the five regions, which is the average particle size of the lithium metal particles.

[0101] As an example, the average particle size of lithium metal particles in this application may be 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm, 100μm, or within the range formed by any two of the above point values ​​as end values.

[0102] Understandably, lithium metal batteries can have a pre-formed lithium metal layer, such as a lithium foil, or they can be used without a pre-formed lithium metal layer, i.e., a "negative electrode-less battery," where the negative electrode only needs to include a negative electrode current collector. During cycling, a layer of lithium metal particles forms on the surface of the lithium foil or directly on the surface of the negative electrode current collector.

[0103] Furthermore, the lithium metal particle layer and / or lithium foil layer are disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0104] In some embodiments, the negative electrode further includes a lithium foil layer located between the negative current collector and the lithium metal particle layer. Further, the thickness of the lithium foil layer is 5 μm to 50 μm; for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any two of the above values ​​as endpoints.

[0105] The negative electrode sheet can be formed by rolling and bonding the lithium foil layer with the negative electrode current collector.

[0106] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction. Further, a layer of lithium metal particles is disposed on either or both of the opposite surfaces of the negative electrode current collector. Further, a lithium foil layer is disposed on either or both of the opposite surfaces of the negative electrode current collector.

[0107] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0108] In some embodiments, the operating temperature of the lithium metal battery is 30°C to 80°C; optionally, it is 40°C to 70°C, and more preferably, it is 50°C to 70°C, 55°C to 70°C, or 50°C to 60°C. Appropriately increasing the charging temperature reduces mass transfer and reaction polarization, further increasing the particle size distribution of lithium deposition. Based on improvements in electrolyte composition combined with temperature optimization, these two improvements work together to achieve large-particle-size, dense lithium deposition, significantly reducing the generation and continuous accumulation of inactive lithium, suppressing irreversible expansion of the cell, and achieving zero or low irreversible expansion. As an example, the operating temperature of the lithium metal battery can be 30°C, 40°C, 50°C, 55°C, 60°C, 70°C, 80°C, or a range defined by two of the above values.

[0109] In some embodiments, the rated charging current of the lithium metal battery is 0.1 mA / cm². 2 ~1mA / cm 2 At this lower charging current, it can also increase the lithium deposition particle size of the lithium metal particle layer.

[0110] 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 a positive electrode active material.

[0111] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0112] In some embodiments, the positive electrode 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 material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0113] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more 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 positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0114] In some embodiments, the positive electrode active material includes Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y A lithium transition metal oxide, wherein 0.2≤x≤1.2, a+b+c=1, 0≤d<1, 0≤y<2, M includes one or more of Zr, Sr, B, Sn, Al, Mg, Fe, Cu, V, Ti, Zr, W, Sb, Dy, and Te, and A includes one or more of N, P, S, and halogen elements. The chemical formula is Li. x (Ni a Co b Mn c ) 1-d M d O 2-y A y Lithium transition metal oxides have high specific capacity, which can further improve the energy density of batteries.

[0115] As some alternative examples of x, x can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, and any value within the range consisting of any two of the above values.

[0116] As some optional examples of d, d can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, and any value within the range of any two of the above values. Optionally, 0 ≤ d ≤ 0.05.

[0117] Furthermore, 0.2 ≤ a ≤ 1. As some alternative examples of a, a can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and any value within the range consisting of any two of the above values.

[0118] Optionally, a×(1-d) can take values ​​from 0.5 to 0.9, for example, 0.5, 0.6, 0.7, 0.8, 0.9.

[0119] As some optional examples of y, y can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, and any value within the range of any two of the above values. Optionally, 0 ≤ y ≤ 0.05.

[0120] Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium cobalt oxides include LiCoO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.

[0121] Optionally, lithium transition metal oxides include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.09 Mn 0.01 O2, LiNi 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc.

[0122] Optionally, the chemical formula is Li x (Ni a Co b Mn c ) 1-d M d O 2-y A y The lithium transition metal oxide accounts for 50% to 100% of the mass of the positive electrode active material. Optionally, the chemical formula is Li. x (Ni a Co b Mn c ) 1-d M d O 2-y A y The percentage of lithium transition metal oxide in the positive electrode active material can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any value within the range of any two of the above values.

[0123] In some embodiments, the positive electrode active material may optionally include a lithium phosphate. Lithium phosphates have a higher cycle life, which can further improve the cycle performance of the battery.

[0124] Optionally, the chemical formula of the lithium phosphate is Li β Fe α M 2 (1-α) PO4, where 0.2≤α≤1, 1≤β≤1.1, M 2 It includes at least one of Ti, V, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, and Sr.

[0125] It is understandable that A includes one or more of N, P, S and halogen elements, where halogen elements can be F, Cl, Br, etc.

[0126] Non-limiting examples of lithium phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0127] Optionally, the lithium phosphate content in the positive electrode active material is 50% to 100% by mass. Optionally, the lithium phosphate content in the positive electrode active material can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any value within the range of any two of the above values.

[0128] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Optionally, the binder accounts for 0.5% to 5% of the mass percentage of the positive electrode active layer. Optionally, the mass percentage of the binder in the positive electrode active layer may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0129] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Optionally, the conductive agent accounts for 0.1% to 5% of the mass percentage of the positive electrode active layer. Optionally, the mass percentage of the conductive agent in the positive electrode active layer may be 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range of any two of the above values.

[0130] In some embodiments, the positive electrode 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 material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0131] In some embodiments, the positive electrode can be prepared by dispersing the components used to prepare the positive electrode, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode through processes such as drying and cold pressing. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0132] Separating membrane

[0133] 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.

[0134] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0135] In some embodiments, the thickness of the isolation membrane is 6~40 μm, optionally 12~20 μm.

[0136] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0137] Another embodiment of this application provides a method for preparing the above-mentioned lithium metal battery, comprising the following steps:

[0138] A lithium metal battery is prepared by injecting the above-mentioned electrolyte into the electrode assembly; wherein the electrode assembly includes the above-mentioned negative electrode and the above-mentioned positive electrode.

[0139] The above preparation method uses the improved electrolyte, and the resulting lithium-ion battery has the advantages mentioned above, which will not be elaborated further here.

[0140] Another embodiment of this application provides an electrical device, including at least one of the above-described lithium metal battery and the lithium metal battery prepared by the above-described preparation method.

[0141] The lithium metal battery and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0142] Typically, a lithium metal battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions deposit and escape between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0143] In some embodiments, the lithium metal battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above. The electrolyte is used to wet the electrode assembly.

[0144] In some embodiments, the outer packaging of the lithium metal battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium metal battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0145] A lithium metal battery includes at least one battery cell. A lithium metal battery may include one or more battery cells.

[0146] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions are inserted and extracted back and forth between the positive and negative electrode plates. The electrolyte plays a role in conducting active ions between the positive and negative electrode plates.

[0147] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1The lithium metal battery shown is a single cell, which serves as an example of a square-structured battery cell.

[0148] In some embodiments, the lithium metal battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above. In some embodiments, the outer packaging of the lithium metal battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium metal battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0149] In some of these embodiments, reference is made 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. 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 within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0150] In some embodiments, the lithium metal battery can be a battery device or a battery pack. A battery device includes at least one battery cell. The number of battery cells in a battery device can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery device.

[0151] Figure 3 This is battery device 4, used as an example. (See reference...) Figure 3 In the battery assembly 4, multiple battery cells 5 can be arranged sequentially along the length of the battery assembly 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0152] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0153] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0154] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery devices 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 devices 4. The multiple battery devices 4 can be arranged in any manner within the battery box.

[0155] In some embodiments, multiple battery cells 5 can also be arranged in any way in the battery box to directly obtain a lithium metal battery.

[0156] In addition, one embodiment of this application also provides an electrical device, which includes the lithium metal battery provided in this application.

[0157] Lithium metal batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can include, for example, mobile phones and laptops; electric vehicles can include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to these.

[0158] As an electrical device, lithium metal batteries can be selected based on its usage requirements.

[0159] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of lithium metal batteries for this electrical device, a battery pack or battery device can be used.

[0160] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0161] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0162] 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 whose manufacturers are not specified are all commercially available conventional products.

[0163] Example 1

[0164] (1) Preparation of the positive electrode sheet:

[0165] Positive electrode active material: lithium nickel cobalt manganese oxide (LiNi) 0.5 Co 0.2 Mn 0.3 O2, conductive agent acetylene black, and binder PVDF were mixed at a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) solvent was added and stirred until the system was uniformly dispersed to obtain the positive electrode slurry. This positive electrode slurry was uniformly coated onto an aluminum foil current collector, air-dried at room temperature, and then transferred to an oven for further drying at 120°C. The completely dried electrode was cut into 40 mm * 50 mm rectangles for subsequent use. The areal capacity of the positive electrode is 3.5 mAh / cm². 2 .

[0166] (2) Preparation of negative electrode sheet:

[0167] A 20μm thick ultrathin lithium strip is rolled onto a 12μm thick copper foil surface and cut into a 41 mm * 51 mm rectangle as the negative electrode sheet.

[0168] (3) Preparation of the diaphragm:

[0169] A polyethylene porous membrane (12 μm thick) was selected and cut into 45 mm × 55 mm cuboids for later use.

[0170] (4) Preparation of electrolytes:

[0171] A mixed solvent was prepared by mixing long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B at a volume ratio of b = 1:1. A lithium salt (lithium bis(fluorosulfonyl)imide) was then added to the mixed solvent and stirred thoroughly to form a colorless and transparent non-aqueous electrolyte. The types of long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B are shown in Table 1. The concentration of the lithium salt in the non-aqueous electrolyte was 1 mol / L.

[0172] (5) Battery assembly:

[0173] Take a pre-cut positive electrode and match it with two pre-cut negative electrodes, separating the positive and negative electrodes with the aforementioned separator, and wrap them in an aluminum-plastic film bag to form a stacked dry cell. Inject 0.2 g of the prepared electrolyte, vacuum heat-press the aluminum-plastic film bag, and let it stand at room temperature for at least 6 hours before starting cycle testing.

[0174] The following are performance tests.

[0175] (1) Cyclic life test.

[0176] The prepared laminated battery cells were subjected to a high-temperature environment of 40℃~80℃ (40℃ in Example 1) at a rate of 0.2C (current density of 0.7 mA / cm²). 2 Charge the battery at 1C rate and discharge it at 2.8~4.3V. When the discharge capacity decays to 80% of the first discharge capacity, the battery life is considered to have ended. Record the corresponding number of cycles. The number of cycles should be rounded to an integer multiple of 10.

[0177] (2) Cell expansion performance.

[0178] The cell expansion performance was tested using the Yuaneng SWE2100 in-situ dilatometer.

[0179] The prepared laminated battery cells were subjected to a constant voltage of 0.5 MPa and a high temperature environment of 40℃~80℃ (40℃ in Example 1) at a rate of 0.2 C (current density of 0.7 mA / cm²). 2 Charge at 1C rate and discharge at 1C rate, with the charging and discharging voltage window set to 2.8~4.3V.

[0180] The thickness of the cell after the first full discharge is defined as m1, and the thickness of the cell after the 200th full discharge is defined as m2. The irreversible expansion rate of the cell is defined as: (m2-m1) / m1×100%.

[0181] (3) Average particle size of lithium metal particles in the negative electrode sheet

[0182] The negative electrode sheet was disassembled, and a 6mm × 6mm sample was cut. Scanning electron microscopy (SEM) was used to test the lithium metal particle layer on the surface of the negative electrode sheet. Five regions containing 10-20 particles of equal area were selected at five locations (corners and center) under the SEM. The particle size was statistically analyzed, and the shortest diagonal dimension was taken as the particle size. The average particle size of the particles in the five regions was obtained, which is the average particle size of the lithium metal particles in the lithium metal particle layer of the negative electrode sheet. Except for Comparative Example 4, the average particle size of the lithium metal particles in other examples and comparative examples was rounded to a multiple of 10.

[0183] Examples 2-4

[0184] The results are basically the same as in Example 1, except that the type of long-chain fluoroether solvent A used is different. The specific parameters and performance results are shown in Table 1.

[0185] Examples 5-6

[0186] The results are basically the same as in Example 1, except that the type of short-chain fluoroether solvent B used is different. The specific parameters and performance results are shown in Table 1.

[0187] Examples 7-8

[0188] The results are basically the same as in Example 1, except that the volume ratio b of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B is different. The specific parameters and performance results are shown in Table 1.

[0189] Examples 9-10

[0190] The results are basically the same as in Example 1, except that the concentration of lithium salt in the electrolyte is different. The specific parameters and performance results are shown in Table 1.

[0191] Examples 11-12

[0192] The results are basically the same as in Example 1, except that the temperature of the high-temperature environment for the cycle life test is different. The specific parameters and performance results are shown in Table 1.

[0193] Comparative Example 1

[0194] The process is basically the same as in Example 1, except that the short-chain fluorinated ether solvent B is omitted in the electrolyte and replaced by an equal volume of long-chain fluorinated ether solvent A. The specific parameters and performance results are shown in Table 1.

[0195] Comparative Example 2

[0196] The process is basically the same as in Example 1, except that the long-chain fluorinated ether solvent A is omitted in the electrolyte and replaced by an equal volume of short-chain fluorinated ether solvent B. The specific parameters and performance results are shown in Table 1.

[0197] Comparative Example 3

[0198] The results are basically the same as those in Example 1, except that an equal volume of a different type of long-chain fluorinated ether solvent A (structural formula III-1) is used instead of the long-chain fluorinated ether solvent A in Example 1. The specific parameters and performance results are shown in Table 1.

[0199] The structure of structural formula III-1 is as follows:

[0200] .

[0201] Comparative Example 4

[0202] The results are basically the same as those in Example 1, except that an equal volume of a different type of long-chain fluorinated ether solvent A (structural formula III-2) is used instead of the long-chain fluorinated ether solvent A in Example 1. The specific parameters and performance results are shown in Table 1.

[0203] The structure of structural formula III-2 is as follows:

[0204] .

[0205] Comparative Example 5

[0206] The process is basically the same as in Example 1, except that the electrolyte solvent is only ethylene glycol dimethyl ether and the cycling temperature is different, as shown in Table 1.

[0207] Table 1

[0208]

[0209] It should be noted that since the cycle life of Comparative Example 5 is less than 200 cycles, its expansion rate test is based on the expansion rate after 120 cycles.

[0210] From Comparative Examples 1 and 2 in Table 1, Comparative Example 1 showed poor cycling performance when using long-chain fluorinated ether solvent A alone; Comparative Example 2 failed to dissolve lithium salts when using short-chain fluorinated ether solvent B alone; and in Comparative Examples 3 and 4, the long-chain fluorinated ether solvent A used ether solvents with R1 being H, resulting in lower cycle lives than the examples. Comparative Example 5 used only ethylene glycol dimethyl ether as its solvent and had a lower cycling temperature, thus resulting in a lower cycle life and a higher expansion rate.

[0211] SEM images of the lithium metal particle layer surface of the negative electrode in the lithium metal battery cell of Comparative Example 5 and Example 1 are shown below. Figure 7 As shown in (a) and (b), the average particle size of lithium metal particles in the lithium metal particle layer in (a) is smaller, with a particle size of about 5 μm, while the average particle size of lithium metal particles in the lithium metal particle layer in (b) is larger and the deposition is more dense, with a particle size of about 50 μm.

[0212] The cell thickness monitoring curves of the lithium metal battery cells of Comparative Example 5 and Example 1 as a function of cycle time are shown below. Figure 8 As shown in (a) and (b) in the figure, it can be seen that the cell thickness of Comparative Example 5 changes more with cycle time, while the cell thickness of Example 1 changes less with cycle time, indicating that its cell expansion rate has been improved.

[0213] As can be seen from Examples 1 to 4, the long-chain fluorinated ether solvent A using compounds of formulas I-1 to I-4 can enable the battery to have good cycle performance and low cell expansion rate. Furthermore, at least one of R2 and R3 includes an ethyl group, which enables the battery to have even better cycle performance and low cell expansion rate.

[0214] As can be seen from Examples 1, 5-6, the use of compounds of formula II-1, II-2, and II-5 in the short-chain fluorinated ether solvent B can enable the battery to have good cycle performance and low cell expansion rate. Furthermore, the better the dispersion of fluorine atoms in R4 and R7 of the short-chain fluorinated ether solvent B, the better the battery can have cycle performance and low cell expansion rate.

[0215] As can be seen from Examples 1 and 7-8, a volume ratio b of 0.2 to 5 between long-chain fluorinated ether solvent A and short-chain fluorinated ether solvent B can give the battery good cycle performance and low cell expansion rate. Further controlling the volume ratio b to 0.5 to 2 can give the battery even better cycle performance and lower cell expansion rate.

[0216] As demonstrated in Examples 1 and 9-10, lithium salt concentrations of 1 mol / L to 3 mol / L can impart good cycle performance and low cell expansion rate to the battery. Furthermore, at lower lithium salt concentrations, increasing the lithium salt concentration can effectively improve the battery's cycle performance; however, at higher lithium salt concentrations, the improvement in cycle performance is limited.

[0217] As shown in Examples 1 and 11, appropriately increasing the charging temperature reduces mass transfer and reaction polarization, further increasing the particle size distribution of lithium deposition, and reducing irreversible cell expansion. As shown in Examples 1 and 12, further controlling the temperature at 50℃~60℃ can enable the battery to achieve both better cycle performance and lower irreversible cell expansion.

[0218] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0219] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the scope of the claims.

Claims

1. A lithium metal battery, characterized in that, The electrolyte comprises a negative electrode, a positive electrode, and an electrolyte; the negative electrode comprises lithium metal, and the electrolyte comprises a lithium salt, a long-chain fluorinated ether solvent A, and a short-chain fluorinated ether solvent B, the structures of which are shown in Formula I and Formula II, respectively. 、 ； R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R'1 includes H, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R2 and R3 each independently include C1-C3 alkyl or fluorinated C1-C3 alkyl; R4 and R7 each independently include F or fluorinated C1-C3 alkyl; R5, R6, R8, and R9 each independently include H or F.

2. The lithium metal battery as described in claim 1, characterized in that, R'1 is H; and / or, The total number of fluorine atoms in R1, R2, and R3 is ≤6; optionally, R2 and R3 each independently include a C1-C3 alkyl group, more preferably, R2 and R3 each independently include a methyl or ethyl group; and / or, The number of fluorine atoms in the fluorinated C1-C3 alkyl group of R1 is ≥2; optionally, R1 includes trifluoromethyl.

3. The lithium metal battery according to any one of claims 1 to 2, characterized in that, The long-chain fluoroether solvent A includes one or more compounds of formulas I-1 to I-4: 。 4. The lithium metal battery according to any one of claims 1 to 3, characterized in that, R4 and R7 each independently include a fluoromethyl or a fluoroethyl group; and / or, the total number of fluorine atoms in R4 and R7 is ≥4; Optionally, the number of fluorine atoms in both R4 and R7 is ≥2; Alternatively, R4 and R7 may each independently include a difluoromethyl or a trifluoromethyl group.

5. The lithium metal battery according to any one of claims 1 to 4, characterized in that, The short-chain fluoroether solvent B comprises one or more compounds of formulas II-1 to II-6: 。 6. The lithium metal battery according to any one of claims 1 to 5, characterized in that, The volume ratio b of the long-chain fluorinated ether solvent A to the short-chain fluorinated ether solvent B is 0.2 to 5; optionally, the volume ratio b is 0.4 to 2.

5.

7. The lithium metal battery according to any one of claims 1 to 6, characterized in that, In the solvent of the electrolyte, the total volume percentage of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B is 90% to 100%.

8. The lithium metal battery according to any one of claims 1 to 7, characterized in that, In the electrolyte, the concentration of the lithium salt is 0.5 mol / L to 5 mol / L, and can be selected as 1 mol / L to 3 mol / L.

9. The lithium metal battery according to any one of claims 1 to 8, characterized in that, The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium dioxalate borate, lithium difluorooxalate borate, lithium nitrate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

10. The lithium metal battery according to any one of claims 1 to 9, characterized in that, The negative electrode sheet further includes a negative current collector and a lithium metal particle layer disposed on the negative current collector. The lithium metal particle layer includes lithium metal particles with an average particle size of 20μm to 100μm, optionally 30μm to 90μm.

11. The lithium metal battery according to claim 10, characterized in that, The negative electrode sheet further includes a lithium foil layer, which is located between the negative electrode current collector and the lithium metal particle layer; Optionally, the thickness of the lithium foil layer is 5μm to 50μm.

12. The lithium metal battery according to any one of claims 1 to 11, characterized in that, The operating temperature of the lithium metal battery is 30℃~80℃; optionally, it is 40℃~70℃.

13. The lithium metal battery according to any one of claims 1 to 12, characterized in that, The rated charging current of the lithium metal battery is 0.1 mA / cm. 2 ~1mA / cm 2 .

14. The lithium metal battery according to any one of claims 1 to 13, characterized in that, The positive electrode sheet includes a positive electrode active material, which includes one or more of the following: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds.

15. A method for preparing a lithium metal battery, characterized in that, Includes the following steps: A lithium metal battery is prepared by injecting an electrolyte into an electrode assembly. The electrode assembly includes a negative electrode and a positive electrode. The negative electrode includes lithium metal. The electrolyte includes a lithium salt, a long-chain fluorinated ether solvent A, and a short-chain fluorinated ether solvent B. The structures of the long-chain fluorinated ether solvent A and the short-chain fluorinated ether solvent B are shown in Formula I and Formula II, respectively. 、 ； R1 includes F, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R'1 includes H, C1-C3 alkyl, or fluorinated C1-C3 alkyl; R2 and R3 each independently include C1-C3 alkyl or fluorinated C1-C3 alkyl; R4 and R7 each independently include F or fluorinated C1-C3 alkyl; R5, R6, R8, and R9 each independently include H or F.

16. The method for preparing a lithium metal battery as described in claim 15, characterized in that, The lithium metal battery prepared by the method described herein is the lithium metal battery as described in any one of claims 2 to 14.

17. An electrical device, characterized in that, It includes at least one of the lithium metal batteries according to any one of claims 1 to 14 and lithium metal batteries prepared by the preparation method according to any one of claims 15 to 16.

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