Lithium metal battery cell and preparation method therefor, battery device and electrical device

Abstract

A lithium metal battery cell (5) and a preparation method therefor, a battery device and an electrical device. The preparation method for the lithium metal battery cell (5) comprises the following steps: assembling a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte to obtain a primary lithium metal battery cell (5), wherein the negative electrode sheet comprises a negative electrode current collector and a lithium-based metal layer located on the negative electrode current collector, the electrolyte comprises an ester additive, and the ester additive comprises at least one of an organic phosphate ester, an organic borate ester, an organic sulfate ester, an organic sulfite ester, and an organic sulfonate ester; at a first temperature, discharging the primary lithium metal battery cell (5) at a first rate current to a first voltage, and after standing for a first time, discharging again at a second rate current to a second voltage, wherein the first rate current is greater than or equal to 1C, the second rate current is less than 1C, the first voltage is greater than the second voltage, and the first voltage is less than a lower limit cut-off voltage of the lithium metal battery cell (5); and after standing for a second time, repeating the discharging process to obtain the lithium metal battery cell (5).

Description

Lithium metal battery cells and their preparation methods, battery devices and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411545308.4, filed on October 31, 2024, entitled “Lithium Metal Battery Cell and Method Thereof for Preparation, Battery Device and Power Consumption Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to a lithium metal battery cell and its preparation method, battery device, and power consumption device. Background Technology

[0004] With the continuous growth of industries such as electric vehicles and aviation, and the booming demand for energy, there is a growing need for battery cells to develop towards higher energy density and greater stability. Lithium metal battery cells have attracted widespread attention due to their higher energy density compared to traditional lithium-ion battery cells. However, lithium metal battery cells suffer from poor high-temperature cycle life. Summary of the Invention

[0005] This disclosure provides a lithium metal battery cell and its preparation method, battery device and power supply device. The lithium metal battery cell prepared by the preparation method of this disclosure has low gas production and long cycle life in high temperature environment.

[0006] In a first aspect, this disclosure provides a method for preparing a lithium metal battery cell, comprising the following steps: assembling a positive electrode, a negative electrode, a separator, and an electrolyte to obtain a primary lithium metal battery cell, wherein the negative electrode includes a negative current collector and a lithium-based metal layer located on the negative current collector, and the electrolyte includes ester additives, wherein the ester additives include at least one selected from organic phosphate esters, organic borate esters, organic sulfate esters, organic sulfite esters, and organic sulfonate esters; discharging the primary lithium metal battery cell to a first voltage at a first temperature with a first rate current, allowing it to stand for a first time, and then discharging it to a second voltage with a second rate current, wherein the first rate current is greater than or equal to 1C, the second rate current is less than 1C, the first voltage is greater than the second voltage, and the first voltage is less than the lower limit cutoff voltage of the lithium metal battery cell; and repeating the discharge process after allowing it to stand for a second time to obtain a lithium metal battery cell.

[0007] The electrolyte of the lithium metal battery cell disclosed herein includes ester additives. Through a low-potential (below the lower cutoff voltage of the lithium metal battery cell) discharge process, the ester additives can preferentially form a flexible and dense positive electrode electrolyte interface film, also known as a CEI film, in situ on the positive electrode surface. During discharge, the lithium metal battery cell is first discharged at a first rate current greater than or equal to 1C, thereby rapidly forming a flexible CEI film in situ on the positive electrode surface, thus reducing the damage to the positive electrode active material structure caused by the low-potential discharge process. Then, the lithium metal battery cell is discharged at a second rate current less than 1C, thereby further optimizing the composition of the CEI film and obtaining a dense CEI film.

[0008] The CEI film formed on the surface of the cathode in this disclosure can protect the cathode active material, improve the structural stability of the cathode active material, and the CEI film can also withstand the volume change of the cathode under high temperature environment. This can reduce the high temperature cycle gas production of the prepared lithium metal battery cell and extend the high temperature cycle life of the lithium metal battery cell.

[0009] In some embodiments, the first rate current is 1C-2C, and / or the second rate current is 0.1C-0.8C, where C is the 1-hour rate discharge current of a lithium metal battery cell.

[0010] Within the aforementioned range, a flexible CEI film can be rapidly generated in situ on the positive electrode surface using the first-rate current, thereby better reducing the damage to the positive electrode active material structure caused by the low-potential discharge process.

[0011] With a second-rate current within the above range, the composition of the CEI film can be further optimized, and a denser CEI film can be obtained.

[0012] In some embodiments, the difference between the second voltage and the over-intercalation voltage of the lithium metal battery cell is greater than -0.3V. This can better reduce the damage to the structure of the positive electrode active material caused by the low-potential discharge process.

[0013] In some embodiments, the first voltage is less than 0.8 times the lower cutoff voltage of the lithium metal battery cell. Using a smaller first voltage facilitates better decomposition of ester additives and helps to form a flexible and dense CEI film in situ on the cathode surface.

[0014] In some embodiments, the mass fraction of ester additives in the electrolyte is 0.2%-5%. Within the above range, the ester additives in the electrolyte can both generate a flexible and dense CEI film in situ on the positive electrode surface through a low-potential discharge process and minimize the impact on the negative electrode, thereby further extending the high-temperature cycle life of lithium metal battery cells.

[0015] In some embodiments, the ester additives include ester compounds containing carbon-carbon unsaturated bonds. These carbon-carbon unsaturated bonds can promote electrochemical polymerization of the ester compound during low-potential discharge, resulting in a more flexible and dense CEI film formed in situ on the positive electrode surface. This further reduces the high-temperature cycle gas generation of the prepared lithium metal battery cell and further extends its high-temperature cycle life.

[0016] In some embodiments, the ester additives include fluorinated ester compounds containing carbon-carbon unsaturated bonds. These carbon-carbon unsaturated bonds in the fluorinated ester compounds can promote electrochemical polymerization during low-potential discharge, resulting in the in-situ formation of a more flexible, dense, and LiF-rich CEI film on the cathode surface. This further reduces the high-temperature cycle gas generation of the prepared lithium metal battery cells and extends their high-temperature cycle life.

[0017] In some embodiments, the ester additives include fluorinated cyclic ester compounds containing carbon-carbon unsaturated bonds. This allows for the in-situ generation of a more flexible, dense, and LiF-rich CEI film on the cathode surface, thereby further reducing the high-temperature cycle gas production of the prepared lithium metal battery cell and further extending the high-temperature cycle life of the lithium metal battery cell.

[0018] In some embodiments, ester additives include at least one of compounds represented by the following general formula.

[0019] R1, R4, R7, R 12 Each is independently selected from C2-C4 alkyl or C2-C4 fluoroalkyl, R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H, F, C1-C4 alkyl or C1-C4 fluoroalkyl, R 27 To R 38 Each of the following is independently selected from C2-C4 alkyl, C2-C4 fluoroalkyl, C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0020] Optionally, R1, R4, R7, R 12 Each is independently selected from C2-C4 fluoroalkyl groups.

[0021] Optionally, R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H or F.

[0022] Optionally, R27 R 28 R 29 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0023] Optionally, R 30 R 31 R 32 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0024] Optionally, R 33 and R 34 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0025] Optionally, R 35 and R 36 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0026] Optionally, R 37 and R 38 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0027] In some embodiments, the ester additive includes at least one of the following compounds.

[0028] In some embodiments, the electrolyte comprises a lithium salt and an organic solvent, the organic solvent including ether solvents.

[0029] In some embodiments, the first temperature is 20°C-60°C.

[0030] In some embodiments, the first time is 3-10 minutes.

[0031] In some embodiments, the second time is 3 min to 10 min.

[0032] In some embodiments, after a second settling period, the discharge process is repeated 1-5 times to obtain a lithium metal battery cell. Repeated low-potential discharge processes can optimize the CEI film composition, helping to obtain a more flexible and dense CEI film, which in turn can better reduce the high-temperature cycle gas generation of the prepared lithium metal battery cell and further extend the high-temperature cycle life of the lithium metal battery cell.

[0033] In some embodiments, the positive electrode sheet 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 includes a positive electrode active material, which includes one or more of lithium phosphate, lithium transition metal oxide, and their respective modified materials.

[0034] Secondly, this disclosure provides a lithium metal battery cell, which is prepared by the preparation method of the first aspect of this disclosure.

[0035] In some embodiments, the mass fraction of ester additives in the electrolyte is 0.05%-3%.

[0036] Thirdly, this disclosure provides a battery device comprising a plurality of lithium metal battery cells according to the second aspect of this disclosure.

[0037] Fourthly, this disclosure provides an electrical device that includes a lithium metal battery cell according to the second aspect of this disclosure or a battery device according to the third aspect of this disclosure. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments of this disclosure will be briefly described below. Obviously, the drawings described below are merely some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0039] Figure 1 shows a schematic diagram of a lithium metal battery cell provided in some embodiments of this disclosure.

[0040] Figure 2 shows a schematic diagram of an electrical device provided in some embodiments of this disclosure.

[0041] The accompanying drawings are not necessarily drawn to scale. Detailed Implementation

[0042] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium metal battery cell, its preparation method, battery device, and power-consuming device of this disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this disclosure and are not intended to limit the subject matter of the claims.

[0043] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of this disclosure may be combined with each other to form new technical solutions, and such technical solutions should be considered as included in the disclosure of this disclosure.

[0045] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions, and such technical solutions should be considered as included in the disclosure of this disclosure.

[0046] Unless otherwise specified, all steps in this disclosure may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] Unless otherwise specified, in this disclosure, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0048] In this disclosure, the terms "multiple" or "a variety" refer to two or more kinds.

[0049] In the description of the embodiments of this disclosure, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] Unless otherwise stated, the terms used in this disclosure have the common meanings as commonly understood by those skilled in the art.

[0051] Unless otherwise stated, the test temperature for all parameters mentioned in this disclosure is 25°C.

[0052] The lithium metal battery cells mentioned in the embodiments of this disclosure can independently perform charging and discharging functions. The lithium metal battery cells may be cylindrical, cuboid, or other shapes, and the embodiments of this disclosure are not limited to these shapes. Figure 1 shows an example of a cuboid lithium metal battery cell 5.

[0053] The battery apparatus mentioned in the embodiments of this disclosure may include one or more battery cell assemblies for providing voltage and capacity. The battery cell assembly may include multiple lithium metal battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0054] In some embodiments, the battery cell assembly is typically formed by arranging multiple lithium metal battery cells.

[0055] As an example, a battery cell assembly can be a battery module, which consists of multiple lithium metal battery cells arranged and fixed together to form an independent module. As another example, a battery module can be formed by bundling multiple lithium metal battery cells together with cable ties.

[0056] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0057] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0058] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple lithium metal battery cells to the housing.

[0059] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0060] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0061] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0062] The technical solutions described in this disclosure are applicable to various electrical devices that use lithium metal battery cells or battery devices, such as, but not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. Lithium metal battery cells and battery devices are used to store or provide electrical energy.

[0063] Figure 2 is a schematic diagram of an example electrical device. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.

[0064] Lithium metal battery cells typically use ether-based electrolytes. Under high voltage, ether-based electrolytes undergo oxidative decomposition on the positive electrode surface. This oxidative decomposition is further accelerated, especially at high temperatures, which affects the reliability and cycle life of lithium metal battery cells in high-temperature environments.

[0065] Based on this, this disclosure provides a method for preparing lithium metal battery cells, and the lithium metal battery cells prepared thereby have low gas production and long cycle life under high temperature environment.

[0066] The method for preparing a lithium metal battery cell disclosed herein includes the following steps: assembling a positive electrode, a negative electrode, a separator, and an electrolyte to obtain a primary lithium metal battery cell; the negative electrode includes a negative current collector and a lithium-based metal layer on the negative current collector; the electrolyte includes ester additives, which include at least one of organic phosphate esters, organic borate esters, organic sulfate esters, organic sulfite esters, and organic sulfonate esters; discharging the primary lithium metal battery cell to a first voltage at a first rate current at a first temperature, allowing it to stand for a first time, and then discharging it to a second voltage at a second rate current; the first rate current is greater than or equal to 1C, the second rate current is less than 1C, the first voltage is greater than the second voltage, and the first voltage is less than the lower cutoff voltage of the lithium metal battery cell; and repeating the discharge process after allowing it to stand for a second time to obtain a lithium metal battery cell.

[0067] The electrolyte of the lithium metal battery cell disclosed herein includes ester additives. Through a low-potential (below the lower cutoff voltage of the lithium metal battery cell) discharge process, the ester additives can preferentially form a flexible and dense positive electrode electrolyte interface film, also known as a CEI film, in situ on the positive electrode surface. During discharge, the lithium metal battery cell is first discharged at a first rate current greater than or equal to 1C, thereby rapidly forming a flexible CEI film in situ on the positive electrode surface, thus reducing the damage to the positive electrode active material structure caused by the low-potential discharge process. Then, the lithium metal battery cell is discharged at a second rate current less than 1C, thereby further optimizing the composition of the CEI film and obtaining a dense CEI film.

[0068] The CEI film formed on the surface of the cathode in this disclosure can protect the cathode active material, improve the structural stability of the cathode active material, and the CEI film can also withstand the volume change of the cathode under high temperature environment. This can reduce the high temperature cycle gas production of the prepared lithium metal battery cell and extend the high temperature cycle life of the lithium metal battery cell.

[0069] In some embodiments, the first multiplier current can be 1C-2C, for example, it can be 1C, 1.1C, 1.2C, 1.3C, 1.4C, 1.5C, 1.6C, 1.7C, 1.8C, 1.9C, 2C, or any range of the above values.

[0070] Within the aforementioned range, a flexible CEI film can be rapidly generated in situ on the positive electrode surface using the first-rate current, thereby better reducing the damage to the positive electrode active material structure caused by the low-potential discharge process.

[0071] Optionally, the first multiplier current can be 1C-1.8C, 1C-1.7C, 1C-1.6C, 1C-1.5C, 1C-1.4C, 1C-1.3C, or 1C-1.2C.

[0072] In some embodiments, the second multiplier current can be 0.1C-0.8C, for example, it can be 0.1C, 0.2C, 0.3C, 0.4C, 0.5C, 0.6C, 0.7C, 0.8C, or any range of the above values.

[0073] With a second-rate current within the above range, the composition of the CEI film can be further optimized, and a denser CEI film can be obtained.

[0074] Optionally, the second rate current can be 0.1C-0.7C, 0.1C-0.6C, 0.1C-0.5C, 0.2C-0.7C, 0.2C-0.6C, 0.2C-0.5C, 0.3C-0.7C, 0.3C-0.6C, or 0.3C-0.5C.

[0075] C represents the hourly discharge current of a single lithium metal battery cell.

[0076] In some embodiments, the difference between the second voltage and the over-lithiation voltage of the lithium metal battery cell can be greater than -0.3V. That is, the difference between the second voltage and the over-lithiation voltage of the lithium metal battery cell is ≥ -0.3V.

[0077] This can better reduce the damage to the structure of the positive electrode active material caused by the low-potential discharge process.

[0078] Optionally, the difference between the second voltage and the over-lithiation voltage of the lithium metal battery cell can be ≥-0.28V, ≥-0.26V, ≥-0.24V, ≥-0.22V, or ≥-0.2V.

[0079] In some embodiments, the first voltage may be less than 0.8 times the lower cutoff voltage of the lithium metal battery cell. Optionally, the first voltage may be less than 0.78 times, 0.76 times, 0.74 times, 0.72 times, 0.7 times, 0.68 times, 0.66 times, 0.64 times, 0.62 times, or 0.6 times the lower cutoff voltage of the lithium metal battery cell.

[0080] Using a smaller initial voltage helps ester additives decompose better and facilitates the in-situ formation of a flexible and dense CEI film on the cathode surface.

[0081] In some embodiments, the first temperature can be 20°C-60°C, for example, it can be 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, or any range of the above values.

[0082] In some embodiments, the first time can be 3 min to 10 min, for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or any range of the above values.

[0083] In some embodiments, the second time can be 3 min to 10 min, for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or any range of the above values.

[0084] In some embodiments, after a second settling period, the discharge process is repeated 1-5 times to obtain a lithium metal battery cell.

[0085] Repeated low-potential discharge processes can optimize the composition of the CEI film, which helps to obtain a more flexible and dense CEI film. This can further reduce the high-temperature cycle gas generation of the prepared lithium metal battery cells and extend the high-temperature cycle life of the lithium metal battery cells.

[0086] Optionally, after a second settling period, the discharge process is repeated 2-5 times to obtain a lithium metal battery cell.

[0087] The discharge process at the first rate current may be the same as or different from the discharge process at the second rate current.

[0088] In some embodiments, the discharge process at the first rate current can be constant current discharge and / or pulse discharge.

[0089] In some embodiments, the discharge process at the second rate current can be constant current discharge and / or pulse discharge.

[0090] In this disclosure, the lower cutoff voltage and over-intercalation voltage of the lithium metal battery cell are both voltages known in the art.

[0091] It is understandable that the discharge process of a lithium metal battery cell is accompanied by the insertion of lithium ions into the positive electrode and a continuous decrease in voltage. When the lithium metal battery cell discharges to the saturated lithium insertion capacity of the positive electrode, the corresponding voltage is considered to be the lower limit cutoff voltage of the lithium metal battery cell. If the discharge continues at this point, the positive electrode will be over-inserted with lithium, that is, it will exceed the capacity limit of the positive electrode active material. The voltage of the lithium metal battery cell will continue to drop to a lower plateau potential, which is considered to be the over-insertion voltage of the lithium metal battery cell.

[0092] For example, positive electrode active materials include lithium transition metal oxides and their modified materials, such as LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25O2 (abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811), LiNi 0.96 Co 0.02 Mn 0.02 O2 (abbreviated as Ni96), LiNi 0.80 Co 0.15 Al 0.05 When O2 is present, the lower cutoff voltage is 2.8V and the over-lithiation voltage is 1.7V; when the positive electrode active material includes lithium phosphate and its modified materials, such as lithium iron phosphate, the lower cutoff voltage is 2.5V and the over-lithiation voltage is 1.4V.

[0093] In some embodiments, the preparation method of a primary lithium metal battery cell may include the following steps: forming an electrode assembly by fabricating a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode; then placing the electrode assembly in an outer packaging and drying it to obtain a lithium metal battery cell to be injected with electrolyte; subsequently, injecting electrolyte into the lithium metal battery cell to be injected with electrolyte, and then allowing it to stand for a period of time to obtain a primary lithium metal battery cell. Optionally, the standing temperature can be 20℃-60℃, for example, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, or any range of the above values. Optionally, the standing time can be 6 hours or more to allow the electrolyte to fully wet the electrode assembly.

[0094] The electrode assembly can be a wound structure or a stacked structure, and the embodiments disclosed herein are not limited to this.

[0095] The outer packaging is used to encapsulate the electrode assembly and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. It can also be a flexible package, such as a pouch. The flexible package material can be plastic, such as one or more of aluminum-plastic film, polypropylene, polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0096] [Positive electrode plate]

[0097] In some embodiments, the positive electrode sheet 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 includes a positive electrode active material, which includes one or more of lithium phosphate, lithium transition metal oxide, and their respective modified materials.

[0098] As an example, lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, and their respective modified materials.

[0099] As an example, lithium transition metal oxides may 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 respective modified materials.

[0100] In some embodiments, to further improve the energy density of lithium metal battery cells, the positive electrode active material may include materials with the general formula Li. a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified materials. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A may include one or more of N, F, S and Cl.

[0101] As an example, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (abbreviated as NCM811), LiNi 0.96 Co 0.02 Mn 0.02 O2 (abbreviated as Ni96), LiNi 0.80 Co 0.15 Al 0.05 One or more of O2, LiFePO4, LiMnPO4 and their respective modified materials.

[0102] The modified materials for the above-mentioned positive electrode active materials can be doped and / or surface coated.

[0103] During the charging and discharging process, lithium metal battery cells undergo lithium (Li) insertion / extraction and consumption, resulting in varying Li molar content at different discharge states. In this disclosure, the molar content of Li in the positive electrode active materials refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to a lithium metal battery cell, the Li molar content changes after charge-discharge cycles. Similarly, the molar content of O in the positive electrode active materials listed in this disclosure is only a theoretical value. Lattice oxygen release causes changes in the O molar content, and the actual O molar content will also fluctuate.

[0104] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. As an example, the positive electrode conductive agent may include, but is not limited to, one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In some embodiments, the positive electrode film layer may further include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0106] In some embodiments, the positive current collector may be a metal foil or a composite current collector. Examples of metal foils include pure metals, alloys, and surface-treated metals, such as aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. Examples of metal materials include, but are not limited to, one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Examples of polymer substrates include, but are not limited to, one or more of polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene.

[0107] The positive electrode film can be formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing positive electrode active materials, positive electrode conductive agents, positive electrode binders, and any other components in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP), but is not limited to this.

[0108] [Negative electrode plate]

[0109] The negative electrode includes a negative current collector and a lithium-based metal layer on the negative current collector. In some embodiments, the lithium-based metal layer may include lithium or a lithium alloy.

[0110] In some embodiments, the negative current collector may be a metal foil. Optionally, as examples of metal foil, pure metal, alloy, or surface-treated metal may be used, such as copper foil, copper alloy foil, nickel foil, nickel alloy foil, etc.

[0111] [Isolation membrane]

[0112] A separator is disposed between the positive and negative electrode plates, primarily serving to prevent internal short circuits. This disclosure does not impose any particular limitation on the type of separator; any known porous membrane with good chemical and mechanical stability can be selected. In some embodiments, the separator material may include, but is not limited to, one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating may also be coated on the surface of the separator.

[0113] Electrolyte

[0114] The electrolyte includes ester additives. In some embodiments, the mass fraction of the ester additives in the electrolyte can be 0.2%-5%, for example, 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%, 2%, 2.1%, 2.2%, 2.3%. %, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5%, or any range of the above values.

[0115] Within the aforementioned range, ester additives in the electrolyte can generate a flexible and dense CEI film in situ on the positive electrode surface through a low-potential discharge process, while minimizing the impact on the negative electrode, thereby further extending the high-temperature cycle life of lithium metal battery cells.

[0116] Optionally, the mass fraction of ester additives in the electrolyte can be 0.5%-5%, 0.5%-4%, 0.5%-3%, 0.8%-5%, 0.8%-4%, 0.8%-3%, 1%-5%, 1%-4%, or 1%-3%.

[0117] In some embodiments, ester additives may include ester compounds containing carbon-carbon unsaturated bonds.

[0118] Ester compounds contain carbon-carbon unsaturated bonds. During low-potential discharge, these bonds can promote electrochemical polymerization of the ester compounds and generate a more flexible and dense CEI film in situ on the positive electrode surface. This can further reduce the high-temperature cycle gas production of the prepared lithium metal battery cells and further extend their high-temperature cycle life.

[0119] Ester compounds may include cyclic ester compounds, chain ester compounds, or a mixture of both. Optionally, ester additives may include cyclic ester compounds containing carbon-carbon unsaturated bonds. This allows for the in-situ generation of a more flexible and dense CEI film on the cathode surface, thereby further reducing the high-temperature cycle gas production of the prepared lithium metal battery cell and further extending the high-temperature cycle life of the lithium metal battery cell.

[0120] In some embodiments, ester additives may include fluorinated ester compounds.

[0121] During low-potential discharge, fluorinated ester compounds can generate a flexible, dense, and LiF-rich CEI film in situ on the cathode surface. LiF helps stabilize the cathode structure, thereby further reducing the high-temperature cycle gas production of the prepared lithium metal battery cell and further extending the high-temperature cycle life of the lithium metal battery cell.

[0122] In some embodiments, ester additives may include fluorinated ester compounds containing carbon-carbon unsaturated bonds.

[0123] Fluorinated ester compounds contain carbon-carbon unsaturated bonds. During low-potential discharge, these bonds can promote the electrochemical polymerization of the ester compounds and generate a more flexible, dense, and LiF-rich CEI film in situ on the cathode surface. This can further reduce the high-temperature cycle gas production of the prepared lithium metal battery cells and further extend their high-temperature cycle life.

[0124] Fluorinated ester compounds may include fluorinated cyclic ester compounds, fluorinated chain ester compounds, or a mixture of both. Optionally, ester additives may include fluorinated cyclic ester compounds containing carbon-carbon unsaturated bonds. This allows for the in-situ generation of a more flexible, dense, and LiF-rich CEI film on the cathode surface, thereby further reducing the high-temperature cycle gas production of the prepared lithium metal battery cell and further extending the high-temperature cycle life of the lithium metal battery cell.

[0125] Carbon-carbon unsaturated bonds can include carbon-carbon double bonds and / or carbon-carbon triple bonds. Optionally, carbon-carbon unsaturated bonds can include carbon-carbon double bonds.

[0126] In some embodiments, ester additives may include at least one of the compounds represented by the following general formula.

[0127] R1, R4, R7, R 12 Each is independently selected from C2-C4 alkyl or C2-C4 fluoroalkyl.

[0128] Optionally, R1, R4, R7, R 12 Each is independently selected from C2-C4 fluoroalkyl groups.

[0129] R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H, F, C1-C4 alkyl or C1-C4 fluoroalkyl.

[0130] Optionally, R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H, F, methyl, or fluoromethyl.

[0131] Alternatively, R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H or F.

[0132] R 27 To R 38 Each of the following is independently selected from C2-C4 alkyl, C2-C4 fluoroalkyl, C2-C4 alkenyl or C2-C4 fluoroalkenyl.

[0133] Optionally, R 27 R 28 R 29 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl. More preferably, R 27 R 28 R 29At least one of them is selected from C2-C4 fluoroalkenyl groups.

[0134] Optionally, R 30 R 31 R 32 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl. More preferably, R 30 R 31 R 32 At least one of them is selected from C2-C4 fluoroalkenyl groups.

[0135] Optionally, R 33 and R 34 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl. More preferably, R 33 and R 34 At least one of them is selected from C2-C4 fluoroalkenyl groups.

[0136] Optionally, R 35 and R 36 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl. More preferably, R 35 and R 36 At least one of them is selected from C2-C4 fluoroalkenyl groups.

[0137] Optionally, R 37 and R 38 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl. More preferably, R 37 and R 38 At least one of them is selected from C2-C4 fluoroalkenyl groups.

[0138] C2-C4 alkyl, C2-C4 fluoroalkyl, C2-C4 alkenyl, and C2-C4 fluoroalkenyl can be either straight-chain or branched-chain structures.

[0139] C2-C4 fluoroalkyl groups can be partially fluoroalkyl or perfluoroalkyl.

[0140] C2-C4 fluoroalkenyl groups can be either partially fluoroalkenyl groups or perfluoroalkenyl groups.

[0141] Optionally, ester additives may include at least one of the compounds represented by the following general formula.

[0142] In some embodiments, as an example, ester additives may include at least one of the following compounds.

[0143] In some embodiments, the electrolyte comprises a lithium salt and an organic solvent.

[0144] In some embodiments, the organic solvent may include ether solvents. Ether solvents may include one or more of chain ether solvents and cyclic ether solvents. Chain ether solvents may include, but are not limited to, one or more of diethyl ether, dipropyl ether, ethylpropyl ether, methyl butyl ether, dibutyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol diethyl ether, propylene glycol diethyl ether, butanediol dimethyl ether, butanediol diethyl ether, and butanediol diethyl ether. Cyclic ether solvents may include, but are not limited to, one or more of tetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxopentane, tetrahydropyran, 1,3-dioxane, and 1,4-dioxane.

[0145] In some embodiments, the lithium salt may include, but is not limited to, one or more of lithium bis(trifluoromethyl)sulfonylimide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiOTF), lithium dioxolaneborate (LiBOB), lithium difluorooxolaneborate (LiDFOB), lithium difluorodioxolane phosphate, and lithium tetrafluorooxolane phosphate.

[0146] Optionally, the lithium salt may include lithium bisfluorosulfonylimide (LiFSI). This lithium salt can decompose on the negative electrode surface to form an inorganic fluorine-rich SEI film component, which is beneficial for the long cycle life of lithium metal battery cells; at the same time, this lithium salt also has relatively good oxidation stability, which can support the cycling of lithium metal battery cells under high voltage.

[0147] In some embodiments, the electrolyte may further include a diluent. Optionally, the diluent may include, but is not limited to, benzene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-dimethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(difluoromethoxy)ethane, 1,2-bis(trifluoromethoxy)ethane, 1,2-diethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, bis(2,2-difluoroethyl) ether, One or more of the following: 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl 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.

[0148] In some embodiments, the lithium salt concentration of the electrolyte can be 1 mol / L to 6 mol / L, for example, it can be 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L, 4 mol / L, 4.2 mol / L, 4.4 mol / L, 4.6 mol / L, 4.8 mol / L, 5 mol / L, 5.2 mol / L, 5.4 mol / L, 5.6 mol / L, 5.8 mol / L, 6 mol / L, or any range of the above values.

[0149] This disclosure also provides a lithium metal battery cell prepared by the method for preparing lithium metal battery cells disclosed herein.

[0150] During the preparation of lithium metal battery cells, ester additives in the electrolyte form a flexible and dense CEI film in situ on the positive electrode surface, thereby reducing the ester additive content in the prepared lithium metal battery cell electrolyte. In some embodiments, the mass fraction of ester additives in the prepared lithium metal battery cell electrolyte can be greater than 0 and less than or equal to 3%.

[0151] Optionally, the mass fraction of ester additives in the prepared lithium metal battery cell electrolyte can be 0.05%-3%, for example, it can be 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%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, or any range of the above values.

[0152] The mass fraction of ester additives in the prepared lithium metal battery cell electrolyte can be obtained by the following method: After disassembling the lithium metal battery cell, take the electrolyte sample from the residual space. Separate the organic solvent, ester additives, and other components from the lithium salt component using gas chromatography. Then, confirm the specific structure of each component using high-precision mass spectrometry and nuclear magnetic resonance spectroscopy. After confirming the specific structure of each component, prepare lithium salt solutions with different standard contents. Fit the relationship between lithium salt content and peak area using ion chromatography. Quantify the lithium salt concentration by testing the electrolyte sample using ion chromatography. Prepare a mixture of organic solvents or ester additives with known proportions, and add a known concentration of a certain organic solvent or ester additive as an internal standard. Obtain the relative correction factor of the peak area and concentration relationship of different components with respect to the internal standard using gas chromatography. Then, test the electrolyte sample with the added known content of internal standard using gas chromatography to obtain the specific proportions of each organic solvent component and ester additive component.

[0153] Example

[0154] The following embodiments describe the contents of this disclosure in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0155] Example 1

[0156] Preparation of the positive electrode: The positive electrode active material LiNi... 0.8 Co 0.1 Mn 0.1O2, acetylene black (positive electrode conductive agent), and polyvinylidene fluoride (PVDF) (positive electrode binder) are mixed in a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP) solvent. The mixture is stirred until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is evenly coated onto both surfaces of the positive electrode current collector aluminum foil, air-dried, and then transferred to an oven for further drying. It is then cut into 40mm × 50mm rectangles to serve as positive electrode sheets. The positive electrode surface capacity is 3.5 mAh / cm². 2 .

[0157] Preparation of negative electrode sheet: A 50μm thick lithium foil is rolled onto a 12μm thick copper foil, and then cut into a 41mm×51mm rectangle as a negative electrode sheet for later use.

[0158] Preparation of the separator membrane: Cut a polyethylene porous membrane into rectangles of 45mm × 55mm as the separator membrane for later use.

[0159] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 1%, based on the total mass of the electrolyte.

[0160] Preparation of lithium metal battery cells: A pre-cut positive electrode sheet is matched with two pre-cut negative electrode sheets, separated by the aforementioned separator, and wrapped in an aluminum-plastic film bag to form a lithium metal battery cell to be injected with electrolyte; 0.3g of electrolyte is injected into the prepared lithium metal battery cell, and then the aluminum-plastic film bag is vacuum heat-sealed and left to stand at 25°C for more than 6 hours to obtain a primary lithium metal battery cell with a capacity of 140mAh; then the primary lithium metal battery cell is discharged, and the discharge process is as follows: at 25°C, firstly, the primary lithium metal battery cell is discharged to 1.7V at 1C (i.e., 140mA), left to stand for 5 minutes, then discharged to 1.5V at 0.5C (i.e., 70mA), left to stand for 5 minutes, and then the discharge process is repeated 4 times to obtain a lithium metal battery cell.

[0161] Comparative Example 1

[0162] Preparation of the positive electrode: The positive electrode active material LiNi... 0.8 Co 0.1 Mn 0.1O2, acetylene black (positive electrode conductive agent), and polyvinylidene fluoride (PVDF) (positive electrode binder) are mixed in a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP) solvent. The mixture is stirred until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is evenly coated onto both surfaces of the positive electrode current collector aluminum foil, air-dried, and then transferred to an oven for further drying. It is then cut into 40mm × 50mm rectangles to serve as positive electrode sheets. The positive electrode surface capacity is 3.5 mAh / cm². 2 .

[0163] Preparation of negative electrode sheet: A 50μm thick lithium foil is rolled onto a 12μm thick copper foil, and then cut into a 41mm×51mm rectangle as a negative electrode sheet for later use.

[0164] Preparation of the separator membrane: Cut a polyethylene porous membrane into rectangles of 45mm × 55mm as the separator membrane for later use.

[0165] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly to obtain the electrolyte. The concentration of LiFSI was 4 mol / L.

[0166] Preparation of lithium metal battery cell: Take a cut positive electrode sheet and two cut negative electrode sheets and match them, separate them with the above-mentioned separator, and wrap them in an aluminum-plastic film bag to form a lithium metal battery cell to be injected with electrolyte; inject 0.3g of electrolyte into the prepared lithium metal battery cell to be injected with electrolyte, and then vacuum heat-press the aluminum-plastic film bag and let it stand at 25°C for more than 6 hours to obtain a lithium metal battery cell with a capacity of 140mAh.

[0167] Comparative Example 2

[0168] Preparation of the positive electrode: The positive electrode active material LiNi... 0.8 Co 0.1 Mn 0.1 O2, acetylene black (positive electrode conductive agent), and polyvinylidene fluoride (PVDF) (positive electrode binder) are mixed in a mass ratio of 98:1:1 and added to N-methylpyrrolidone (NMP) solvent. The mixture is stirred until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is evenly coated onto both surfaces of the positive electrode current collector aluminum foil, air-dried, and then transferred to an oven for further drying. It is then cut into 40mm × 50mm rectangles to serve as positive electrode sheets. The positive electrode surface capacity is 3.5 mAh / cm². 2 .

[0169] Preparation of negative electrode sheet: A 50μm thick lithium foil is rolled onto a 12μm thick copper foil, and then cut into a 41mm×51mm rectangle as a negative electrode sheet for later use.

[0170] Preparation of the separator membrane: Cut a polyethylene porous membrane into rectangles of 45mm × 55mm as the separator membrane for later use.

[0171] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 1%, based on the total mass of the electrolyte.

[0172] Preparation of lithium metal battery cell: Take a cut positive electrode sheet and two cut negative electrode sheets and match them, separate them with the above-mentioned separator, and wrap them in an aluminum-plastic film bag to form a lithium metal battery cell to be injected with electrolyte; inject 0.3g of electrolyte into the prepared lithium metal battery cell to be injected with electrolyte, and then vacuum heat-press the aluminum-plastic film bag and let it stand at 25°C for more than 6 hours to obtain a lithium metal battery cell with a capacity of 140mAh.

[0173] Performance testing

[0174] (1) High temperature cycle life test

[0175] Set the ambient temperature to 60℃, and charge the prepared lithium metal battery cell at a constant current of 0.2C (i.e., 28mA). After reaching the cutoff voltage of 4.3V, continue charging at a constant voltage of 4.3V until the current decays to 0.1C (i.e., 14mAh). Then discharge the lithium metal battery cell at 1C (i.e., 140mA) to 2.8V. Perform charge and discharge cycles according to the above process. When the discharge capacity decays to 80% of the first discharge capacity, the lithium metal battery cell is considered to have reached the end of its lifespan. Record the number of cycles when the lithium metal battery cell reaches the end of its lifespan.

[0176] (2) Normalized gas production test

[0177] Take the prepared lithium metal battery cell and obtain the volume V1 of the lithium metal battery cell before cycle testing by the water displacement method.

[0178] The ambient temperature was set to 60℃. The prepared lithium metal battery cells were charged at a constant current of 0.2C (28mA) until the cutoff voltage of 4.3V was reached. Then, they were charged at a constant voltage of 4.3V until the current decreased to 0.1C (14mAh). The lithium metal battery cells were then discharged at 1C (140mA) to 2.8V. This charge-discharge cycle was repeated. When the discharge capacity decreased to 80% of the first cycle's discharge capacity, the lithium metal battery cell was considered to have reached the end of its lifespan. After fully discharging the lithium metal battery cell that had reached the end of its lifespan, its volume V2 after the cycle test was obtained again using the water displacement method. The difference between V2 and V1 is the gas production volume V. Dividing the gas production volume V by the total charging capacity of the lithium metal battery cell gives the normalized gas production of the battery cell. The total charging capacity of the lithium metal battery cell is equal to the sum of the charging capacities per cycle.

[0179] Table 1

[0180] As can be seen from the above test results, the lithium metal battery cells prepared by adding ester additives to the electrolyte and using a low-potential discharge process have low cycle gas production and long cycle life under high temperature conditions.

[0181] Comparative Example 2 only added ester additives to the electrolyte, but did not perform low-potential discharge treatment. The resulting lithium metal battery cell still had high gas production and poor cycle life under high-temperature conditions. This is because the ester additives cannot form a high-performance CEI film on the cathode surface before the start of cycling.

[0182] Example 2

[0183] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0184] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 2%, based on the total mass of the electrolyte.

[0185] Example 3

[0186] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0187] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 3%, based on the total mass of the electrolyte.

[0188] Example 4

[0189] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0190] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 4%, based on the total mass of the electrolyte.

[0191] Example 5

[0192] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0193] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 5%, based on the total mass of the electrolyte.

[0194] Example 6

[0195] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0196] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 0.5%, based on the total mass of the electrolyte.

[0197] Example 7

[0198] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0199] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 1 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 1 was 0.2%, based on the total mass of the electrolyte.

[0200] Table 2

[0201] The test results above show that further adjusting the content of ester additives in the prepared electrolyte can further extend the high-temperature cycle life of lithium metal battery cells and further reduce the cycle gas production of lithium metal battery cells.

[0202] Example 8

[0203] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0204] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 2 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 2 was 1%, based on the total mass of the electrolyte.

[0205] Example 9

[0206] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0207] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 3 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 3 was 1%, based on the total mass of the electrolyte.

[0208] Example 10

[0209] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0210] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 4 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 4 was 1%, based on the total mass of the electrolyte.

[0211] Example 11

[0212] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0213] Electrolyte preparation: Lithium bis(fluorosulfonyl)imide (LiFSI) was added to ethylene glycol dimethyl ether and stirred thoroughly. Then, ester additive compound 5 was added and stirred until homogeneous to obtain the electrolyte. The concentration of LiFSI was 4 mol / L, and the mass fraction of compound 5 was 1%, based on the total mass of the electrolyte.

[0214] Table 3

[0215] The test results above show that using fluorinated cyclic ester compounds containing carbon-carbon unsaturated bonds can further extend the high-temperature cycle life of lithium metal battery cells and further reduce the cycle gas production of lithium metal battery cells.

[0216] Example 12

[0217] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0218] Preparation of lithium metal battery cells: A pre-cut positive electrode sheet is matched with two pre-cut negative electrode sheets, separated by the aforementioned separator, and wrapped in an aluminum-plastic film bag to form a lithium metal battery cell to be injected with electrolyte; 0.3g of electrolyte is injected into the prepared lithium metal battery cell, and then the aluminum-plastic film bag is vacuum heat-sealed and left to stand at 25°C for more than 6 hours to obtain a primary lithium metal battery cell with a capacity of 140mAh; then the primary lithium metal battery cell is discharged, and the discharge process is as follows: at 25°C, firstly, the primary lithium metal battery cell is discharged to 1.7V at 1.5C (i.e., 210mA), left to stand for 5 minutes, then discharged to 1.5V at 0.5C (i.e., 70mA), left to stand for 5 minutes, and then the discharge process is repeated 4 times to obtain a lithium metal battery cell.

[0219] Example 13

[0220] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0221] Preparation of lithium metal battery cells: A pre-cut positive electrode sheet and two pre-cut negative electrode sheets are matched and separated by the aforementioned separator. The mixture is then wrapped in an aluminum-plastic film bag to form a lithium metal battery cell to be injected with electrolyte. 0.3g of electrolyte is injected into the prepared lithium metal battery cell. The aluminum-plastic film bag is then vacuum-sealed and allowed to stand at 25°C for at least 6 hours to obtain a primary lithium metal battery cell with a capacity of 140mAh. The primary lithium metal battery cell is then discharged using the following process: At 25°C, the primary lithium metal battery cell is first discharged to 1.7V at 1.5C (210mA), allowed to stand for 5 minutes, and then discharged to 1.5V at 0.8C (112mA), allowed to stand for 5 minutes, and then the discharge process is repeated four times to obtain the lithium metal battery cell.

[0222] Table 4

[0223] The test results above show that further adjustment of the low-potential discharge process parameters can further extend the high-temperature cycle life of lithium metal battery cells and further reduce the cycle gas production of lithium metal battery cells.

[0224] Example 14

[0225] Except for the following differences, the preparation method of the lithium metal battery cell is the same as that in Example 1.

[0226] Preparation of lithium metal battery cells: A pre-cut positive electrode sheet is matched with two pre-cut negative electrode sheets, separated by the aforementioned separator, and wrapped in an aluminum-plastic film bag to form a lithium metal battery cell to be injected with electrolyte; 0.3g of electrolyte is injected into the prepared lithium metal battery cell to be injected with electrolyte, and then the aluminum-plastic film bag is vacuum heat-sealed and left to stand at 25°C for more than 6 hours to obtain a primary lithium metal battery cell with a capacity of 140mAh; then the primary lithium metal battery cell is discharged, and the discharge process is as follows: at 25°C, firstly, the primary lithium metal battery cell is discharged to 1.7V at 1C (i.e., 140mA), left to stand for 5 minutes, then discharged to 1.5V at 0.5C (i.e., 70mA), left to stand for 5 minutes, and then the above discharge process is repeated once to obtain a lithium metal battery cell.

[0227] Table 5

[0228] The test results above show that repeated low-potential discharge processes can further extend the high-temperature cycle life of lithium metal battery cells and further reduce the cycle gas production of lithium metal battery cells.

[0229] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this disclosure are included within the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included within the scope of this disclosure without departing from the spirit of this disclosure.

Claims

1. A method for preparing a lithium metal battery cell, comprising the following steps: A primary lithium metal battery cell is obtained by assembling a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative current collector and a lithium-based metal layer on the negative current collector. The electrolyte includes ester additives, which include at least one of organic phosphate esters, organic borate esters, organic sulfate esters, organic sulfite esters, and organic sulfonate esters. At a first temperature, the primary lithium metal battery cell is discharged to a first voltage at a first rate current, and after standing for a first time, it is discharged to a second voltage at a second rate current. The first rate current is greater than or equal to 1C, the second rate current is less than 1C, the first voltage is greater than the second voltage, and the first voltage is less than the lower limit cutoff voltage of the lithium metal battery cell. After a second settling period, the discharge process is repeated to obtain lithium metal battery cells.

2. The preparation method according to claim 1, wherein, The first rate current is 1C-2C, and / or the second rate current is 0.1C-0.8C, where C is the 1-hour rate discharge current of the lithium metal battery cell.

3. The preparation method according to any one of claims 1-2, wherein, The difference between the second voltage and the over-lithiation voltage of the lithium metal battery cell is greater than -0.3V.

4. The preparation method according to any one of claims 1-3, wherein, The first voltage is less than 0.8 times the lower limit cutoff voltage of the lithium metal battery cell.

5. The preparation method according to any one of claims 1-4, wherein, The mass fraction of the ester additive in the electrolyte is 0.2%-5%.

6. The preparation method according to any one of claims 1-5, wherein, The ester additives include ester compounds containing carbon-carbon unsaturated bonds.

7. The preparation method according to any one of claims 1-6, wherein, The ester additives include fluorinated ester compounds containing carbon-carbon unsaturated bonds.

8. The preparation method according to any one of claims 1-7, wherein, The ester additives include fluorinated cyclic ester compounds containing carbon-carbon unsaturated bonds.

9. The preparation method according to any one of claims 1-8, wherein, The ester additives include at least one of the compounds represented by the following general formula. R1, R4, R7, R 12 Each is independently selected from C2-C4 alkyl or C2-C4 fluoroalkyl. R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H, F, C1-C4 alkyl, or C1-C4 fluoroalkyl. R 27 To R 38 Each of the following is independently selected from C2-C4 alkyl, C2-C4 fluoroalkyl, C2-C4 alkenyl or C2-C4 fluoroalkenyl.

10. The preparation method according to claim 9, wherein, R1, R4, R7, R 12 Each is independently selected from C2-C4 fluoroalkyl groups; and / or, R2, R3, R5, R6, R8 to R 11 R 13 To R 26 Each is independently selected from H or F; and / or, R 27 R 28 R 29 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl; and / or, R 30 R 31 R 32 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl; and / or, R 33 and R 34 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl; and / or, R 35 and R 36 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl; and / or, R 37 and R 38 At least one of them is selected from C2-C4 alkenyl or C2-C4 fluoroalkenyl.

11. The preparation method according to any one of claims 1-10, wherein, The ester additives include at least one of the following compounds.

12. The preparation method according to any one of claims 1-11, wherein, The electrolyte comprises lithium salt and organic solvent, wherein the organic solvent includes ether solvent.

13. The preparation method according to any one of claims 1-12, wherein, The first temperature is 20℃-60℃; and / or, The first time is 3 min-10 min; and / or, The second time is 3 min to 10 min.

14. The preparation method according to any one of claims 1-13, wherein, After a second settling period, the discharge process is repeated 1-5 times to obtain lithium metal battery cells.

15. The preparation method according to any one of claims 1-14, wherein, 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 includes a positive electrode active material, which includes one or more of lithium phosphate, lithium transition metal oxide and their respective modified materials.

16. A lithium metal battery cell, prepared by the preparation method according to any one of claims 1-15.

17. The lithium metal battery cell according to claim 16, wherein, The mass fraction of the ester additive in the electrolyte is 0.05%-3%.

18. A battery device comprising a plurality of lithium metal battery cells as described in any one of claims 16-17.

19. An electrical device comprising a lithium metal battery cell as described in any one of claims 16-17 or a battery device as described in claim 18.

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