Lithium metal battery and preparation method thereof, and electric device

Abstract

The application provides a lithium metal battery and a preparation method thereof and an electric device. The lithium metal battery comprises a positive electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a crystalline first lithium salt. The electrolyte comprises a second lithium salt, a third lithium salt and a first solvent. The first lithium salt and the second lithium salt comprise lithium bisfluorosulfonylimide, and the third lithium salt comprises lithium difluorophosphate. The lithium metal battery can balance good safety performance and cycle performance.

Description

Technical Field

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

[0002] With the continuous growth of industries such as electric vehicles and aviation, and the booming demand for energy, lithium batteries are being developed towards higher energy density and greater stability. Compared with traditional lithium-ion batteries, lithium metal batteries have higher energy density and longer cycle life, and have now become an important part of the future energy field.

[0003] The negative electrode of lithium metal batteries uses extremely reactive elemental lithium, which is prone to safety issues such as thermal runaway, and is one of the key factors limiting the application of lithium metal batteries. Traditional methods have improved the safety of lithium metal batteries by coating the electrode surface or introducing electrolyte additives, but the improvement effect is limited, and it also reduces the cycle performance of the battery. Summary of the Invention

[0004] Based on this, this application provides a lithium metal battery that balances safety and cycle performance, as well as its preparation method and power application device.

[0005] In a first aspect, this application provides a lithium metal battery, comprising a positive electrode and an electrolyte, wherein the positive electrode comprises a positive active layer, the positive active layer comprises a crystalline first lithium salt, and the electrolyte comprises a second lithium salt, a third lithium salt and a first solvent; the first lithium salt and the second lithium salt comprise lithium bis(fluorosulfonyl)imide, and the third lithium salt comprises lithium difluorooxalateborate.

[0006] The aforementioned lithium metal battery, based on the use of LiFSI and LiDFOB as the electrolyte lithium salt, incorporates the pre-embedding of crystalline LiFSI in the positive electrode active layer of the positive electrode sheet, thereby achieving a comprehensive improvement in the cycle performance and safety performance of the lithium metal battery and effectively reducing the risk of thermal runaway of the lithium metal battery.

[0007] In some embodiments, the mass percentage of lithium bisfluorosulfonylimide in the positive electrode active layer is 5% to 15%. By rationally controlling the amount of LiFSI pre-embedded in the positive electrode active layer, a high concentration level can be maintained at the electrode, while reducing the impact of LiFSI addition on the polarization and porosity of the positive electrode, thus achieving better battery cycle performance.

[0008] In some embodiments, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium difluorooxalate borate in the electrolyte is (0.4~1):1. Properly controlling the molar ratio of the second lithium salt to the third lithium salt can achieve better cycle performance while reducing the risk of thermal runaway.

[0009] In some embodiments, the molar amount of the second lithium salt in the electrolyte is denoted as n1, the molar amount of the third lithium salt as n2, and the molar amount of the first solvent as n3. n1, n2, and n3 satisfy the condition: (n1 + n2) / n3 = 0.5~0.8. By controlling n1, n2, and n3 to meet the above range, the second and third lithium salts in the electrolyte can be maintained in a saturated state. This is beneficial for the LiFSI pre-embedded in the positive electrode to remain in a crystalline state within the electrode, reducing side reactions and maintaining a high LiFSI concentration at the electrode, thus improving cycle performance.

[0010] In some embodiments, the first solvent includes one or more of ether solvents, non-fluorinated ester solvents, and fluoroethylene carbonate, difluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl 2,2,2-trifluoroacetate, and ethyl 2,2,2-trifluoroacetate.

[0011] In some embodiments, the electrolyte further includes a diluent. In the electrolyte, the molar amount of the second lithium salt is denoted as n1, the molar amount of the third lithium salt as n2, the molar amount of the first solvent as n3, and the molar amount of the diluent as n4. n1, n2, and n3 satisfy the formula: (n1 + n2 + n3): n4 = 1.5~2. By adding an appropriate amount of diluent, the viscosity of the electrolyte can be adjusted, which helps to simplify the battery manufacturing process.

[0012] In some embodiments, the diluent includes one or more of fluorinated ether solvents, fluorinated aromatic solvents, and fluorinated saturated alkane solvents.

[0013] In some embodiments, the first lithium salt accounts for ≤30% of the total mass of the second and third lithium salts; optionally, it is 15% to 30%. By controlling this percentage, the ratio of LiFSI to LiDFOB can be adjusted during cycling to achieve a balance between cycling performance and safety.

[0014] In some embodiments, the positive electrode active layer has one or more of the following characteristics:

[0015] (1) The positive electrode active layer comprises a positive electrode active material, which comprises a lithium layered transition metal oxide, and optionally includes a ternary material;

[0016] (2) The porosity of the positive electrode active layer is 10%~25%.

[0017] By pre-embedding an appropriate amount of LiFSI in the positive electrode active layer, a suitable porosity of the positive electrode active layer can be obtained, resulting in better battery cycle performance.

[0018] In some embodiments, the lithium metal battery includes a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including lithium metal.

[0019] A second aspect of this application provides a method for preparing a lithium metal battery, comprising the following steps:

[0020] A precursor solution including a first lithium salt is applied to the positive electrode active layer, and then dried to prepare a positive electrode sheet;

[0021] The battery assembly including the positive electrode is assembled into a cell, and an electrolyte is injected into the cell, the electrolyte including a second lithium salt, a third lithium salt and a first solvent, to prepare the lithium metal battery;

[0022] The first lithium salt and the second lithium salt comprise lithium bis(fluorosulfonyl)imide, and the third lithium salt comprises lithium difluorooxalate borate.

[0023] In some embodiments, the precursor fluid has one or more of the following characteristics:

[0024] (1) The precursor liquid includes a second solvent, which includes an ether solvent;

[0025] (2) The mass percentage of the first lithium salt in the precursor solution is 5%~20%.

[0026] In some embodiments, the drying temperature is 50°C to 80°C.

[0027] A third aspect of this application provides an electrical device comprising at least one of the lithium metal battery described in the first aspect and the lithium metal battery prepared by the preparation method described in the second aspect. Attached Figure Description

[0028] 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:

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

[0030] Figure 2 for Figure 1 An exploded view of a lithium metal battery according to an embodiment of this application is shown.

[0031] Figure 3 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.

[0032] Figure 4 This is a SEM image of the surface of the positive electrode in a lithium metal battery according to an embodiment of this application.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Lithium metal battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0035] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0037] 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; 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 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 "a~b" 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" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0038] 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.

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

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Traditional methods mainly improve the safety of lithium metal batteries, such as thermal runaway, by coating the electrode surface or introducing electrolyte additives. However, these methods reduce the battery's cycle performance, so traditional methods cannot balance the safety and cycle performance of lithium metal batteries.

[0045] Research has shown that one of the main reasons for the thermal runaway behavior of lithium metal batteries at high temperatures is the exothermic reaction between lithium salts in the electrolyte and the positive and negative electrodes. The heat generation from the reaction between the anions of different lithium salts varies significantly. Lithium bisfluorosulfonylimide (LiFSI) can achieve good cycle performance when applied to lithium metal batteries, but its exothermic reaction is relatively intense. Lithium difluorooxalate borate (LiDFOB) has a smaller exothermic reaction (about 1 / 10 of that of LiFSI), but its cycle performance is poor.

[0046] This application initially attempted to use a combination of LiFSI and LiDFOB as lithium salts in the electrolyte, but the improvement in battery cycle performance remained limited. Through further research, this application, while using LiFSI and LiDFOB as lithium salts in the electrolyte, incorporates a suitable amount of LiFSI pre-embedded in the positive electrode active layer of the positive electrode. This pre-embedded LiFSI, distinct from the LiFSI dissolved in the electrolyte, is in a crystalline state. Thus, during cycling, the pre-embedded LiFSI can maintain a high concentration level at the electrode, thereby improving cycle performance. This results in a better overall improvement in the safety and cycle performance of lithium metal batteries.

[0047] One embodiment of this application provides a lithium metal battery, including a positive electrode and an electrolyte. The positive electrode includes a positive active layer, which includes a crystalline first lithium salt. The electrolyte includes a second lithium salt, a third lithium salt, and a first solvent. The first and second lithium salts include lithium bis(fluorosulfonyl)imide (LiFSI), and the third lithium salt includes lithium difluorooxalate borate (LiDFOB).

[0048] The aforementioned lithium metal battery, based on the use of LiFSI and LiDFOB as the electrolyte lithium salt, incorporates the pre-embedding of crystalline LiFSI in the positive electrode active layer of the positive electrode sheet, thereby achieving a comprehensive improvement in the cycle performance and safety performance of the lithium metal battery and effectively reducing the risk of thermal runaway of the lithium metal battery.

[0049] In some embodiments, the mass percentage of lithium bisfluorosulfonylimide in the positive electrode active layer is 5% to 15%. By rationally controlling the amount of LiFSI pre-embedded in the positive electrode active layer, a high concentration level can be maintained at the electrode, while reducing the impact of LiFSI addition on the polarization and porosity of the positive electrode, thus achieving better battery cycle performance. Specifically, the mass percentage of lithium bisfluorosulfonylimide in the positive electrode active layer includes, but is not limited to: 5%, 8%, 10%, 12%, 15%, or any range between the foregoing.

[0050] In some embodiments, the molar ratio of lithium bis(fluorosulfonyl)imide to lithium difluorooxalate borate in the electrolyte is (0.4~1):1. Specifically, this molar ratio includes, but is not limited to, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, or any range between the foregoing. Reasonably controlling the molar ratio of the second lithium salt to the third lithium salt can achieve better cycle performance while reducing the risk of thermal runaway.

[0051] In some embodiments, the molar amount of the second lithium salt in the electrolyte is denoted as n1, the molar amount of the third lithium salt as n2, and the molar amount of the first solvent as n3. n1, n2, and n3 satisfy the condition: (n1+n2) / n3 = 0.5~0.8. By controlling n1, n2, and n3 to meet the above range, the second and third lithium salts in the electrolyte can be maintained in a saturated state. This is beneficial for the LiFSI pre-embedded in the positive electrode to remain in a crystalline state within the electrode, reducing side reactions and maintaining a high LiFSI concentration at the electrode, thus improving cycle performance. Specifically, the value of (n1+n2) / n3 includes, but is not limited to, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or any two of the aforementioned values.

[0052] Without limitation, the first solvent may be a type of solvent conventionally used in lithium metal batteries.

[0053] In some embodiments, the first solvent includes one or more of ether solvents, non-fluorinated ester solvents, and fluoroethylene carbonate, difluoroethylene carbonate, methyltrifluoroethyl carbonate, ethyltrifluoroethyl carbonate, and di(2,2,2-trifluoroethyl) carbonate.

[0054] Specifically, non-fluorinated ester solvents include, but are not limited to, one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate; ether solvents may include, but are not limited to, methyl ether, diethyl ether, propyl ether, butyl ether, methyl ethyl ether, methyl propyl ether, methyl butyl ether, ethyl propyl ether, ethyl butyl ether, propyl butyl ether, dimethoxymethane, diethoxymethane, dipropoxymethane, dimethoxyethane, dimethoxypropane, diethoxyethane, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane.

[0055] In some embodiments, the electrolyte further includes a diluent. In the electrolyte, the molar amount of the second lithium salt is denoted as n1, the molar amount of the third lithium salt as n2, the molar amount of the first solvent as n3, and the molar amount of the diluent as n4. n1, n2, and n3 satisfy the condition: (n1 + n2 + n3):n4 = 1.5~2. By adding an appropriate amount of diluent, the viscosity of the electrolyte can be adjusted, which helps to simplify the battery manufacturing process. Specifically, the value of (n1 + n2 + n3):n4 includes, but is not limited to, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any range between the foregoing.

[0056] Without limitation, the diluent includes one or more of fluorinated ether solvents, fluorinated aromatic solvents, and fluorinated saturated alkane solvents.

[0057] Specifically, the diluents include, but are not limited to, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoro One or more of the following: ethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl-2,2,3,3-tetrafluoropropyl ether, perfluoroisopropylmethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

[0058] In some embodiments, the first lithium salt accounts for ≤30% of the total mass of the second and third lithium salts. By controlling this percentage, a balance between cycling performance and safety can be achieved by adjusting the ratio of LiFSI to LiDFOB during cycling. Specifically, this percentage includes, but is not limited to, 1%, 5%, 10%, 15%, 20%, 25%, 30%, or any range between the foregoing. Further, the first lithium salt accounts for 15% to 30% of the total mass of the second and third lithium salts.

[0059] In some embodiments, the porosity of the positive electrode active layer is 10% to 25%. By pre-embedding an appropriate amount of LiFSI in the positive electrode active layer, a suitable porosity can be obtained, resulting in better battery cycle performance.

[0060] In other embodiments of this application, a method for preparing a lithium metal battery is provided, comprising the following steps:

[0061] A precursor solution including a first lithium salt is applied to the positive electrode active layer, and then dried to prepare a positive electrode sheet;

[0062] The battery assembly including the positive electrode is assembled into a cell, and an electrolyte is injected into the cell, the electrolyte including a second lithium salt, a third lithium salt and a first solvent, to prepare the lithium metal battery;

[0063] The first lithium salt and the second lithium salt comprise lithium bis(fluorosulfonyl)imide, and the third lithium salt comprises lithium difluorooxalate borate.

[0064] Understandably, the lithium metal batteries prepared by the above method are similar to the aforementioned lithium metal batteries, possessing similar technical solutions and advantages, which will not be elaborated upon here.

[0065] Without limitation, the precursor solution includes a second solvent, which includes ether solvents. Specifically, the second solvent includes, but is not limited to, one or more of the following: methyl ether, diethyl ether, propyl ether, butyl ether, methyl ethyl ether, methyl propyl ether, methyl butyl ether, ethyl propyl ether, ethyl butyl ether, propyl butyl ether, dimethoxymethane, diethoxymethane, dipropoxymethane, dimethoxyethane, dimethoxypropane, diethoxyethane, ethylene glycol methyl ethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane.

[0066] Without limitation, the mass percentage of the first lithium salt in the precursor solution is 5% to 20%. Specifically, this mass percentage includes, but is not limited to, 5%, 10%, 15%, 20%, or any range between the two mentioned above.

[0067] Without limitation, the drying temperature is 50°C to 80°C. Specifically, the drying temperature includes, but is not limited to: 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or any range between the foregoing. Understandably, the purpose of the drying process is primarily to remove the second solvent, and the drying time can be determined based on the drying conditions.

[0068] In other embodiments of this application, an electrical device is also provided, including a lithium metal battery as described above or a lithium metal battery prepared by the preparation method described above.

[0069] The lithium metal battery and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0070] Typically, a lithium metal 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 extracting. 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.

[0071] 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.

[0072] 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.

[0073] 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).

[0074] 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-containing phosphates with an olivine structure, lithium layered 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. Examples of lithium layered transition metal oxides include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), 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-containing phosphates with an olivine structure 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 iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 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 LiNi0.6 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 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0075] In some embodiments, the positive electrode active material includes a ternary material.

[0076] In some embodiments, the positive electrode active material 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.

[0077] In some embodiments, the positive electrode active material 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.

[0078] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, 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 sheet after drying, cold pressing, and other processes. 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 or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the areal density per unit area of ​​the coating, based on dry weight (excluding solvent), can be 15 mg / cm³. 2 ~35mg / cm 2 The compaction density of the positive electrode sheet can be 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option.3 ~3.5g / cm 3 .

[0079] The negative electrode includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, wherein the negative active layer includes lithium metal. Understandably, for lithium metal batteries, using lithium metal as the negative active layer can be achieved by directly laminating lithium metal foil onto the surface of the negative current collector, or by using a "no-negative-electrode" approach, where the negative electrode only uses the negative current collector, and lithium metal gradually deposits on the surface of the negative current collector during cycling to form a lithium metal layer.

[0080] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0081] 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).

[0082] The electrolyte serves to conduct ions between the positive and negative electrodes. The electrolyte used in this application is as described above and will not be repeated here.

[0083] 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.

[0084] 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.

[0085] In some embodiments, the lithium metal 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.

[0086] 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.

[0087] In some embodiments, the thickness of the isolation membrane is 6μm to 40μm, and optionally 12μm to 20μm.

[0088] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0089] 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.

[0090] 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, or a steel shell. 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.

[0091] A lithium metal battery includes at least one battery cell. A lithium metal battery may include one or more battery cells.

[0092] 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 move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0093] 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 1 Here is an example of a square-structured lithium metal battery 1.

[0094] In some of these embodiments, reference is made to Figure 2The outer packaging may include a housing 11 and a cover plate 13. The housing 11 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 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The lithium metal battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0095] Lithium metal batteries can be battery modules or battery packs.

[0096] A battery module includes at least one battery cell. The number of battery cells in a battery module 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 module.

[0097] In a battery module, multiple battery cells can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these battery cells can be secured using fasteners.

[0098] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0099] 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. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0100] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0101] In addition, this application also provides an electrical device, which includes the lithium metal battery provided in this application. The lithium metal battery 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, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, 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.

[0102] As an electrical device, lithium metal batteries can be selected based on its usage requirements.

[0103] Figure 3 Here is an example of an electrical device 2. 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 module can be used.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] Example 1

[0108] 1) Preparation of positive electrode sheet

[0109] The positive electrode active material NCM811, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed and dispersed in the solvent N-methylpyrrolidone at a mass ratio of 98:1:1 to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on both sides of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying to form the positive electrode active layer. The resulting layer was then cut into 40mm×50mm rectangles to serve as the positive electrode sheet, with a positive electrode surface capacity of 3.5mAh / cm². 2 .

[0110] 2) Pre-embedded positive electrode sheet

[0111] LiFSI was added to DME to prepare a 10wt% LiFSI / DME precursor solution. 200μL of the LiFSI / DME precursor solution was dropped onto the positive active layer of the positive electrode. The positive electrode was then dried in a 60℃ oven for more than 2 hours to ensure that there was no DME solvent residue, thus obtaining a positive electrode with pre-embedded LiFSI, wherein the mass percentage of LiFSI in the positive active layer was 10%.

[0112] The results of SEM analysis of the positive electrode active layer of the positive electrode are as follows: Figure 4 As shown, the positive electrode active layer contains crystalline LiFSI particles, which appear as light gray granules. The porosity of the positive electrode active layer was determined to be 15% using mercury porosimetry.

[0113] 3) Preparation of negative electrode sheet

[0114] A 50μm thick lithium foil is coated onto a 12μm thick copper foil using a single-sided roll forming method, and then cut into a 41mm×51mm rectangle to serve as the negative electrode.

[0115] 4) Separating membrane

[0116] A 14μm thick polyethylene porous membrane was selected and cut into rectangles of 45 mm * 55 mm as the separator.

[0117] 4) Preparation of electrolyte

[0118] LiFSI and LiDFOB were mixed in an organic solvent (molecular weight n3 = 2 mol) at a molar ratio of n1:n2 = 0.5 mol: 0.5 mol. The organic solvent was dimethyl ethylene glycol ether (DME). At this point, the electrolyte was a saturated solution, with (n1 + n2) / n3 = 0.5. Then, a diluent (molecular weight n4 = 2 mol, (n1 + n2 + n3): n4 = 1.5) was added to this saturated solution. The diluent was 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). After uniform mixing, a mixed salt electrolyte was prepared. At the same time, the percentage of LiFSI in the positive electrode active layer relative to the total mass of LiFSI and LiDFOB in the electrolyte was 22%.

[0119] 5) Battery manufacturing

[0120] A positive electrode sheet pre-embedded with LiFSI is matched with two pre-cut negative electrode sheets, and the positive and negative electrodes are separated by the aforementioned separator. The electrodes are then wrapped in an aluminum-plastic film bag to form a stacked dry cell. 0.3g of the previously prepared electrolyte is injected, and the aluminum-plastic film bag is vacuum-sealed using a thermoforming process. After standing at room temperature for at least 6 hours, a lithium metal battery is obtained. The rated capacity of the stacked battery prepared by this method is 140 mAh.

[0121] The lithium metal battery preparation methods provided in Examples 2 and 3 are the same as those in Example 1, except that the molar ratio of LiFSI and LiDFOB in the electrolyte is different.

[0122] The lithium metal battery preparation methods provided in Examples 4 and 5 are the same as those in Example 1, except that the mass percentage of LiFSI in the positive electrode active layer is different.

[0123] The lithium metal battery preparation methods provided in Examples 6 and 7 are the same as those in Example 1, except that the percentage of LiFSI in the positive electrode active layer relative to the total mass of LiFSI and LiDFOB in the electrolyte is different.

[0124] The lithium metal battery preparation method provided in Comparative Example 1 is the same as that in Example 1, except that: LiFSI is not pre-embedded in the positive electrode active layer, and LiDFOB is not used in the electrolyte to supplement the total molar amount of lithium salt in the electrolyte with LiFSI.

[0125] The lithium metal battery preparation method provided in Comparative Example 2 is the same as that in Example 1, except that: LiFSI is not pre-embedded in the positive electrode active layer, and LiFSI is not used in the electrolyte; instead, LiDFOB is used to supplement the total molar amount of lithium salt in the electrolyte.

[0126] The lithium metal battery preparation method provided in Comparative Example 3 is the same as that in Example 1, except that LiFSI is not pre-embedded in the positive electrode active layer.

[0127] The main parameters of the examples and comparative examples are summarized in Table 1 below:

[0128] Table 1

[0129]

[0130] Test example:

[0131] (1) High-temperature cycle life test method:

[0132] The ambient temperature was set to 60℃. The lithium metal battery was charged at 0.2C (28mA) until the cutoff voltage of 4.3V was reached. Then, it was charged at a constant voltage of 4.3V until the current decreased to 0.1C (14 mAh). Finally, it was discharged at 1C (140 mA) to 2.8V. This charge-discharge cycle was repeated. When the discharge capacity decreased to 80% of the capacity of the first discharge cycle, the battery life was considered to have ended. The number of cycles at the end of the battery life was recorded.

[0133] (2) Dsc heat generation test method:

[0134] After fully charging a lithium metal battery, remove the aluminum-plastic film and cut a 3mm diameter disc from the electrode area. Place the disc in a crucible for DSC testing. Operating mode: HWS mode; Calorimeter bomb: 8mL volume, Hastelloy (specific heat 0.425 J·g) -1 ·k -1 ); Glove box atmosphere replacement vacuum degree: -0.085MPa; Glove box protective atmosphere: nitrogen.

[0135] The test results are shown in Table 2 below:

[0136] Table 2

[0137]

[0138] A comparison between Examples 1-7 and Comparative Example 1 shows that although Comparative Example 1 achieves a higher cycle life, it exhibits very intense heat release. It should also be noted that, compared to Example 1, the cycle life of Comparative Example 1 also shows a certain degree of decrease.

[0139] The comparison between Examples 1-7 and Comparative Examples 2 and 3 shows that although Comparative Examples 2 and 3 have less heat release, their cycle life has decreased significantly.

[0140] 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.

[0141] 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.

Claims

1. A lithium metal battery, characterized in that, The device includes a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive active layer, which includes a crystalline first lithium salt. The electrolyte includes a second lithium salt, a third lithium salt, and a first solvent. The first and second lithium salts include lithium difluorosulfonylimide, and the third lithium salt includes lithium difluorooxalate borate.

2. The lithium metal battery of claim 1, wherein, The mass percentage of lithium bis(fluorosulfonyl)imide in the positive electrode active layer is 5% to 15%.

3. The lithium metal battery according to claim 1, characterized in that, In the electrolyte, the molar ratio of lithium difluorosulfonylimide to lithium difluorooxalate borate is (0.4~1):

1.

4. The lithium metal battery according to claim 1, characterized in that, In the electrolyte, the molar amount of the second lithium salt is denoted as n1, the molar amount of the third lithium salt is denoted as n2, and the molar amount of the first solvent is denoted as n3. n1, n2, and n3 satisfy the following condition: (n1+n2) / n3=0.5~0.

8.

5. The lithium metal battery according to any one of claims 1 to 4, characterized in that, The first solvent includes one or more of the following: ether solvents, non-fluorinated ester solvents, and fluoroethylene carbonate, difluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl 2,2,2-trifluoroacetate, and ethyl 2,2,2-trifluoroacetate.

6. The lithium metal battery according to any one of claims 1 to 4, characterized in that, The electrolyte also includes a diluent. In the electrolyte, the molar amount of the second lithium salt is denoted as n1, the molar amount of the third lithium salt is denoted as n2, the molar amount of the first solvent is denoted as n3, and the molar amount of the diluent is denoted as n4. n1, n2, and n3 satisfy the following: (n1+n2+n3):n4=1.5~2.

7. The lithium metal battery according to claim 6, characterized in that, The diluent includes one or more of fluorinated ether solvents, fluorinated aromatic solvents, and fluorinated saturated alkane solvents.

8. The lithium metal battery according to any one of claims 1 to 4, characterized in that, The percentage of the first lithium salt in the total mass of the second and third lithium salts is ≤30%.

9. The lithium metal battery according to claim 8, characterized in that, The first lithium salt accounts for 15% to 30% of the total mass of the second and third lithium salts.

10. The lithium metal battery according to any one of claims 1 to 4, characterized in that, The positive electrode active layer has one or more of the following characteristics: (1) The positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises a lithium layered transition metal oxide; (2) The porosity of the positive electrode active layer is 10%~25%.

11. The lithium metal battery according to claim 10, characterized in that, The positive electrode active material includes ternary materials.

12. The lithium metal battery according to any one of claims 1 to 4, characterized in that, The lithium metal battery includes a negative electrode sheet, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including lithium metal.

13. A method for preparing a lithium metal battery, characterized in that, Includes the following steps: A precursor solution comprising a first lithium salt is applied to the positive electrode active layer and then dried to prepare a positive electrode sheet, such that the positive electrode active layer comprises a crystalline first lithium salt. The battery assembly including the positive electrode is assembled into a cell, and an electrolyte is injected into the cell, the electrolyte including a second lithium salt, a third lithium salt and a first solvent, to prepare the lithium metal battery; The first lithium salt and the second lithium salt comprise lithium bis(fluorosulfonyl)imide, and the third lithium salt comprises lithium difluorooxalate borate.

14. The method for preparing a lithium metal battery according to claim 13, characterized in that, The precursor fluid has one or more of the following characteristics: (1) The precursor liquid includes a second solvent, which includes an ether solvent; (2) The mass percentage of the first lithium salt in the precursor solution is 5%~20%.

15. The method for preparing a lithium metal battery according to claim 13 or 14, characterized in that, The drying temperature is 50℃~80℃.

16. An electrical appliance, characterized in that, It includes at least one of the lithium metal batteries according to any one of claims 1 to 12 and lithium metal batteries prepared by the preparation method according to any one of claims 13 to 15.

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