Lithium metal battery cell and method of making same, battery device, and power using device

Abstract

This application provides a lithium metal battery cell, its preparation method, battery device, and power consumption device. The lithium metal battery cell of this application includes at least one electrode assembly, comprising a positive electrode, a negative electrode, and a separator between them; the negative electrode includes a negative current collector and a negative electrode interface layer located on at least one side of the negative current collector, the negative electrode interface layer being located between the negative current collector and the separator; a constant pressure is maintained on opposite sides of the electrode assembly along its thickness direction; the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88; wherein, the cyclic thickness change of the electrode assembly is the average value of the thickness change of the electrode assembly before and after each charge and discharge cycle, in μm; the theoretical lithium metal thickness change of the electrode assembly is calculated according to the following formula: The cyclic performance and safety performance of the lithium metal battery cell of this application are significantly improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium metal battery cell, a method for preparing the lithium metal battery cell, a battery device, and an electrical device. Background Technology

[0002] In recent years, with the increasingly wide range of applications, lithium metal batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of lithium metal batteries, higher requirements have been placed on their cycle performance and safety performance. Summary of the Invention

[0003] This application was made in view of the above-mentioned problems, and its purpose is to provide a lithium metal battery cell, a method for preparing the lithium metal battery cell, a battery device, and an electrical device. The lithium metal battery cell of this application has significantly improved cycle performance and safety performance.

[0004] To achieve the above objectives, the first aspect of this application provides a lithium metal battery cell, including at least one electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; the negative electrode includes a negative current collector and a negative interface layer located on at least one side of the negative current collector, the negative interface layer being located between the negative current collector and the separator.

[0005] The electrode assembly has constant pressure on opposite sides along the thickness direction;

[0006] The ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88; wherein,

[0007] The cyclic thickness change of the electrode assembly is the average of the thickness change of the electrode assembly before and after each charge and the thickness change of the electrode assembly before and after each discharge in the charge-discharge cycle, in μm. The charge-discharge cycle is performed by charging to 4.3V with a constant current of 0.2C and then discharging to 2.8V with a constant current of 0.5C.

[0008] The theoretical lithium metal thickness variation of the electrode assembly is calculated according to the following formula:

[0009]

[0010] Where h represents the theoretical lithium metal thickness variation of the electrode assembly, in μm; Y represents the average charge and discharge capacity of the electrode assembly in each charge-discharge cycle, in Ah, wherein the charge-discharge cycle is performed by charging at a constant current of 0.2C to 4.3V and then discharging at a constant current of 0.5C to 2.8V; F represents the Faraday constant, in C / mol; M represents the molar mass of lithium, in g / mol; and ρ represents the density of lithium, in g / cm³. 3 A represents the area of ​​the overlap of the positive electrode, the separator, and the negative electrode in the electrode assembly, in cm². 2 .

[0011] Therefore, this application has a constant pressure on both sides of the electrode assembly along the thickness direction and makes the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change ≥0.88. As the amount of lithium metal deposited during charging increases, it can effectively suppress the deposited lithium metal from entering the negative electrode interface layer and destroying its structure, thereby suppressing the growth of lithium dendrites and improving the cycle performance and safety performance of the battery cell.

[0012] In any embodiment, the ratio of the cycle thickness change of the electrode assembly to the theoretical lithium metal thickness change is 0.88-1.35 or 0.95-1.03. Therefore, this ratio range can, on the one hand, suppress the increase in internal stress of the electrode assembly with increasing lithium metal deposition, thereby inhibiting the deposited lithium metal from entering and damaging the structure of the negative electrode interface layer, suppressing lithium dendrite growth, and thus improving the cycle performance of the battery cell; on the other hand, it improves the density of lithium deposition, suppresses the expansion of the battery cell, reduces the contact between lithium metal and electrolyte, and reduces side reactions between them, thereby improving the cycle performance and safety performance of the battery cell.

[0013] In any embodiment, the constant pressure is 0.5MPa-2MPa or 1MPa-1.5MPa. Therefore, this constant pressure range, on the one hand, helps to improve the density of the deposited lithium metal, suppress the expansion of the battery cells, reduce side reactions in contact between lithium metal and the electrolyte, and also helps to improve the adhesion between the separator and the negative electrode interface layer, reducing the impedance between the separator and the negative electrode interface layer, thereby improving the cycle performance and fast-charging performance of the battery cells; on the other hand, it reduces the impact of increased constant pressure on the deposited lithium metal entering and damaging the interface layer.

[0014] In any embodiment, the compaction density of the negative electrode interface layer is 0.6 g / cm³. 3 -1.5g / cm 3 or 0.8g / cm 3 -1.2g / cm 3Therefore, on the one hand, it helps to inhibit the deposited lithium metal from entering the negative electrode interface layer and destroying the structure of the negative electrode interface layer, thus inhibiting the failure of the negative electrode interface layer and improving the cycle performance of the battery cell. At the same time, it helps to increase the contact sites between the negative electrode interface layer and the separator to reduce the interface impedance. On the other hand, it helps to reduce the impact of the increased compaction density of the negative electrode interface layer on lithium-ion conduction.

[0015] In any embodiment, the negative electrode interface layer comprises carbon-based material particles with an average particle size of 1 nm-10 μm or 50 nm-1 μm. Therefore, on the one hand, limiting the upper limit of the average particle size of the carbon-based material particles can reduce the porosity in the negative electrode interface layer, which helps to inhibit the deposited lithium metal from entering the negative electrode interface layer and damaging its structure, thereby reducing the failure of the negative electrode interface layer and improving the cycle performance of the battery cell. Simultaneously, it helps to increase the contact sites between the negative electrode interface layer and the separator, thus reducing interfacial impedance. On the other hand, limiting the lower limit of the average particle size of the carbon-based material particles can reduce the impact of reduced porosity in the negative electrode interface layer on lithium-ion conduction.

[0016] In any embodiment, the average roughness Ra of the negative electrode current collector on the side facing the negative electrode interface layer is 0.1-0.8 μm or 0.2-0.4 μm. This, on the one hand, limits the upper limit of the average roughness, which helps improve the uniformity of the electric field distribution on the surface of the negative electrode current collector and suppresses the formation of lithium dendrites; on the other hand, limits the lower limit of the average roughness, which helps improve the electrical contact between lithium and the negative electrode current collector during lithium deposition, while simultaneously reducing the requirements for manufacturing processes and lowering production costs.

[0017] A second aspect of this application provides a method for preparing lithium metal battery cells, comprising the following steps:

[0018] The lithium metal battery cell includes at least one electrode assembly. A constant pressure is applied to opposite sides of the electrode assembly along its thickness direction, or to opposite sides of the lithium metal battery cell along the thickness direction of the electrode assembly, while simultaneously satisfying that the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88; wherein,

[0019] The electrode assembly includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; the negative electrode includes a negative current collector and a negative interface layer located on at least one side of the negative current collector, the negative interface layer being located between the negative current collector and the separator.

[0020] The cyclic thickness change of the electrode assembly is the average of the thickness change of the electrode assembly before and after each charge and the thickness change of the electrode assembly before and after each discharge in the charge-discharge cycle, in μm. The charge-discharge cycle is performed by charging to 4.3V with a constant current of 0.2C and then discharging to 2.8V with a constant current of 0.5C.

[0021] The theoretical lithium metal thickness variation of the electrode assembly is calculated according to the following formula:

[0022]

[0023] Where h represents the theoretical lithium metal thickness variation of the electrode assembly, in μm; Y represents the average charge and discharge capacity of the electrode assembly in each charge-discharge cycle, in Ah, wherein the charge-discharge cycle is performed by charging at a constant current of 0.2C to 4.3V and then discharging at a constant current of 0.5C to 2.8V; F represents the Faraday constant, in C / mol; M represents the molar mass of lithium, in g / mol; and ρ represents the density of lithium, in g / cm³. 3 A represents the area of ​​the overlap of the positive electrode, the separator, and the negative electrode in the electrode assembly, in cm². 2 .

[0024] Therefore, this application applies a constant pressure to opposite sides of the electrode assembly along the thickness direction or to opposite sides of the lithium metal battery cell along the thickness direction of the electrode assembly, and maintains the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change at ≥0.88. As the amount of lithium metal deposited during battery cell charging increases, it can effectively suppress the deposited lithium metal from entering the negative electrode interface layer and damaging its structure, maintaining the integrity of the negative electrode interface layer structure, suppressing lithium dendrite growth, thereby improving the cycle performance and safety performance of the battery cell.

[0025] In any embodiment, the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is 0.88-1.35 or 0.95-1.03.

[0026] In any embodiment, the constant pressure is 0.5MPa-2MPa or 1MPa-1.5MPa.

[0027] In any embodiment, the negative electrode interface layer is prepared by the following steps:

[0028] A negative electrode interface slurry is coated onto one or both sides of the negative electrode current collector facing the separator, and then dried and optionally cold-pressed to obtain a negative electrode interface layer located on at least one side of the negative electrode current collector.

[0029] In any embodiment, the compaction density of the negative electrode interface layer is 0.6 g / cm³. 3 -1.5g / cm 3 or 0.8g / cm 3 -1.2g / cm 3 .

[0030] In any embodiment, the negative electrode interface layer comprises carbon-based material particles, the average particle size of which is 1 nm-10 μm or 50 nm-1 μm.

[0031] In any embodiment, the average roughness Ra of the negative electrode current collector on the side facing the negative electrode interface layer is 0.1-0.8 μm or 0.2-0.4 μm.

[0032] A third aspect of this application provides a battery device, including a lithium metal battery cell as described in the first aspect of this application or a lithium metal battery cell prepared by the method described in the second aspect of this application.

[0033] The fourth aspect of this application provides an electrical device, including a lithium metal battery cell as described in the first aspect of this application, a lithium metal battery cell prepared by the method described in the second aspect of this application, or a battery device as described in the third aspect of this application. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of a stacked electrode assembly;

[0036] Figure 2 It is a cross-sectional view of the cuboid-shaped wound electrode assembly;

[0037] Figure 3 This is a cross-sectional view of a cylindrical wound electrode assembly;

[0038] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0039] Figure 5 yes Figure 4 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0040] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application.

[0041] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0042] Figure 8 yes Figure 7 An exploded view of a battery pack according to one embodiment of this application is shown.

[0043] Figure 9 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0044] Figure 10 This is a SEM image of the cross-section of the negative electrode sheet along the thickness direction in Embodiment 1 of this application;

[0045] Figure 11 This is a SEM image of the cross-section of the negative electrode sheet along the thickness direction in Comparative Example 2;

[0046] Figure 12 This is a partial SEM image of the cross-section of the negative electrode sheet along the thickness direction in Comparative Example 2.

[0047] The accompanying drawings are not drawn to scale.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly; 6 Negative electrode current collector; 7 Lithium metal; 8 Negative electrode interface layer. Detailed Implementation

[0050] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0051] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium metal battery and its preparation method, positive electrode, negative electrode, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0052] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0053] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0054] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0055] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0056] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0057] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0058] [Rechargeable Battery]

[0059] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0060] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (such as lithium ions) repeatedly insert and extract (or deposit and peel off) between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also positioned between the positive and negative electrodes, mainly serves to conduct active ions.

[0061] One embodiment of this application provides a lithium metal battery cell, including at least one electrode assembly, the electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator membrane located between the positive electrode sheet and the negative electrode sheet; the negative electrode sheet includes a negative current collector and a negative electrode interface layer located on at least one side of the negative current collector, the negative electrode interface layer being located between the negative current collector and the separator membrane;

[0062] The electrode assembly has constant pressure on opposite sides along the thickness direction;

[0063] The ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88, for example, ≥0.90, ≥0.95, ≥1.00, ≥1.03, or any range of the above values; wherein,

[0064] The cyclic thickness change of the electrode assembly is the average of the thickness change of the electrode assembly before and after each charge and the thickness change of the electrode assembly before and after each discharge in the charge-discharge cycle, in μm. The charge-discharge cycle is performed by charging to 4.3V with a constant current of 0.2C and then discharging to 2.8V with a constant current of 0.5C.

[0065] The theoretical lithium metal thickness variation of the electrode assembly is calculated according to the following formula:

[0066]

[0067] Where h represents the theoretical lithium metal thickness variation of the electrode assembly, in μm; Y represents the average charge and discharge capacity of the electrode assembly in each charge-discharge cycle, in Ah, wherein the charge-discharge cycle is performed by charging at a constant current of 0.2C to 4.3V and then discharging at a constant current of 0.5C to 2.8V; F represents the Faraday constant, in C / mol; M represents the molar mass of lithium, in g / mol; and ρ represents the density of lithium, in g / cm³. 3 A represents the area of ​​the overlap of the positive electrode, the separator, and the negative electrode in the electrode assembly, in cm². 2 .

[0068] In this application, the theoretical lithium metal thickness change of the electrode assembly refers to the thickness change of the electrode assembly theoretically caused by the deposition / stripping of lithium ions during charge-discharge cycles.

[0069] Existing negative electrode-less lithium metal battery cells typically consist of a negative current collector and a negative electrode interface layer located on at least one side of the current collector. During the charge-discharge cycle of a lithium metal battery cell, lithium metal is deposited / stripped between the negative current collector and the negative electrode interface layer. Since lithium metal battery cells usually employ a constant-gap charge-discharge cycle mode, as the amount of lithium metal deposited between the negative current collector and the negative electrode interface layer increases during charging, the internal stress of the electrode assembly gradually increases. The deposited lithium metal can easily creep into the negative electrode interface layer, damaging its structure. This can easily lead to the breakage and failure of the negative electrode interface layer, causing lithium dendrite growth that punctures the separator, resulting in a decrease in the cycle performance of the battery cell.

[0070] To solve the above-mentioned technical problems, the applicant unexpectedly discovered that: the present application has a constant pressure on the opposite sides of the electrode assembly along the thickness direction and makes the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change ≥0.88. In this way, as the amount of lithium metal deposited during charging increases, the increase of internal stress in the electrode assembly can be effectively suppressed, so as to suppress the deposited lithium metal from entering the negative electrode interface layer and destroying its structure, maintain the integrity of the negative electrode interface layer structure, suppress lithium dendrite growth, and thus improve the cycle performance and safety performance of the battery cell.

[0071] In some embodiments, the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is 0.88-1.35 or 0.95-1.03, for example, 0.88, 0.9, 1.0, 1.03, 1.1, 1.2, 1.3, 1.35 or any range of the above values.

[0072] The low density of deposited lithium metal in existing lithium metal battery cells easily leads to cell expansion, affecting the cell's cycle performance. Therefore, the aforementioned ratio range can, on the one hand, suppress the increase in internal stress of the electrode assembly with increasing lithium metal deposition, thereby inhibiting the deposited lithium metal from entering and disrupting the structure of the negative electrode interface layer, suppressing lithium dendrite growth, and thus improving the cell's cycle performance; on the other hand, it improves the density of lithium deposition, suppresses cell expansion, reduces the contact between lithium metal and electrolyte, and reduces side reactions between them, thereby improving the cell's cycle performance and safety.

[0073] In this application, the method for testing the cyclic thickness change of the electrode assembly includes: charging a lithium metal battery cell to 4.3V at a constant current of 0.2C, then discharging it to 2.8V at a constant current of 0.5C, and performing multiple charge-discharge cycles in this manner (e.g., multiple charge-discharge cycles until the cycle capacity retention rate reaches 80%), testing the electrode assembly thickness change before and after each charge and before and after each discharge (e.g., using a distance sensor for testing), and taking the average value as the cyclic thickness change of the electrode assembly.

[0074] In this application, the test method for the average value Y of the charging capacity and the discharging capacity of the electrode assembly during each charge-discharge cycle includes: charging the lithium metal battery cell to 4.3V at a constant current of 0.2C, then discharging it to 2.8V at a constant current of 0.5C, and performing multiple charge-discharge cycles in this manner (e.g., performing multiple charge-discharge cycles until the cycle capacity retention rate reaches 80%), and summing the charging capacity and discharging capacity of all cycles to obtain the average value.

[0075] In this application, the Faraday constant F is generally considered to be 96485.33289±0.00059C / mol.

[0076] In this application, the density of lithium refers to the density of lithium under standard conditions (usually 20°C), which is generally 0.534 g / cm³. 3 .

[0077] In this application, the molar mass of lithium is generally 6.941 g / mol.

[0078] In this application, in multiple electrode assemblies, the area of ​​the positive electrode, the separator, and the negative electrode in each electrode assembly is equal.

[0079] In this application, the area of ​​overlap between the positive electrode, separator, and negative electrode in the electrode assembly can be tested using conventional methods in the art. For example, it can be done by disassembling the battery cell, removing the positive electrode, separator, and negative electrode from the electrode assembly, cutting off the non-overlapping parts of the three, and measuring the remaining part to obtain the area of ​​overlap between the positive electrode, separator, and negative electrode.

[0080] In this application, the thickness direction of the electrode assembly is as conventionally understood in the art. For example, as Figure 1 As shown, for stacked electrode assemblies, the "thickness direction of the electrode assembly" can be understood as the direction in which the positive electrode, separator, and negative electrode are stacked, i.e. Figure 1 The X1 direction. For example, for a cuboid wound electrode assembly, the electrode assembly includes three directions: length (X2), width (Y2), and height (the height direction is perpendicular to the plane formed by the length and width). Figure 2 This is a cross-sectional view of a cuboid-shaped wound electrode assembly. The electrode assembly is wound along its length (X2) and width (Y2) directions, where the length dimension in the X2 direction is greater than the width dimension in the Y2 direction. The "thickness direction of the electrode assembly" can be understood as the width (Y2) direction. For example, for a cylindrical wound electrode assembly, the electrode assembly includes a radial (D) direction and a height direction (the height direction of the cylinder). Figure 3 This is a cross-sectional view of a cylindrical wound electrode assembly, where the "thickness direction of the electrode assembly" can be understood as the radial direction (D) of the cylinder. The change in the thickness of the electrode assembly is the change in the dimensional value along the thickness direction of the electrode assembly.

[0081] In some embodiments, the constant pressure is 0.5MPa-2MPa or 1MPa-1.5MPa, for example, 0.5MPa, 0.8MPa, 1MPa, 1.2MPa, 1.5MPa, 1.7MPa, 2MPa or any range of the above values.

[0082] Existing lithium metal battery cells typically employ a constant-gap charge-discharge cycle mode, which can easily lead to loose adhesion between the separator and the negative electrode interface layer. This results in a high interfacial impedance between the separator and the negative electrode interface layer, affecting the fast-charging performance of the battery cell. Therefore, the aforementioned constant pressure range has two advantages: firstly, it helps to improve the density of deposited lithium metal, suppress battery cell expansion, reduce side reactions between lithium metal and electrolyte, and improve the adhesion between the separator and the negative electrode interface layer, reducing the impedance between them, thereby improving the cycle performance and fast-charging performance of the battery cell; secondly, it reduces the impact of increasing the constant pressure on the deposited lithium metal entering and damaging the interface layer.

[0083] In this application, constant pressure is implemented in any feasible manner, such as by applying a constant pressure testing fixture that can display the applied pressure in real time.

[0084] In some embodiments, the compaction density of the negative electrode interface layer is 0.6 g / cm³. 3 -1.5g / cm 3 or 0.8g / cm 3 -1.2g / cm3 For example, 0.6 g / cm³ 3 0.8g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.2g / cm 3 1.3g / cm 3 1.5g / cm 3 Or any range of the above values. Therefore, on the one hand, it helps to suppress the deposited lithium metal from entering the negative electrode interface layer and damaging its structure, thereby inhibiting the failure of the negative electrode interface layer and improving the cycle performance of the battery cell. Simultaneously, it helps to increase the contact sites between the negative electrode interface layer and the separator to reduce interface impedance. On the other hand, it helps to reduce the impact of increased compaction density of the negative electrode interface layer on lithium-ion conduction.

[0085] In this application, the compaction density of the negative electrode interface layer can be tested using conventional methods in the art. For example, the following specific method can be used: disassemble the battery cell, remove the negative electrode sheet and clean and dry it with an organic solvent, cut a fixed area of ​​negative electrode sheet and weigh it, weigh the same area of ​​negative electrode current collector beforehand, measure the average thickness of the negative electrode interface layer on the negative electrode sheet; subtract the weight of the negative electrode current collector from the weight of the negative electrode sheet, and then divide by the fixed area to obtain the areal density of the negative electrode interface layer; divide the areal density of the negative electrode interface layer by the average thickness of the negative electrode interface layer to obtain the compaction density of the negative electrode interface layer.

[0086] In some embodiments, the negative electrode interface layer comprises carbon-based material particles with an average particle size of 1 nm-10 μm or 50 nm-1 μm, such as 1 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 700 nm, 800 nm, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any combination of the above values. Thus, on the one hand, limiting the upper limit of the average particle size of the carbon-based material particles can reduce the porosity in the negative electrode interface layer, which is beneficial for inhibiting the deposited lithium metal from entering the negative electrode interface layer and damaging its structure, thereby reducing the failure of the negative electrode interface layer and improving the cycle performance of the battery cell. Simultaneously, it helps to increase the contact sites between the negative electrode interface layer and the separator to reduce interfacial impedance. On the other hand, limiting the lower limit of the average particle size of the carbon-based material particles can reduce the impact of reduced porosity in the negative electrode interface layer on lithium-ion conduction.

[0087] In this application, the average particle size of the carbon-based material particles can be tested using conventional methods in the art. For example, the following specific method can be used: disassemble the battery cell, remove the negative electrode sheet and clean it with an organic solvent, and use a scanning electron microscope (e.g., ZEISS Sigma 300) to obtain a scanning electron microscope (SEM) image of the negative electrode sheet, referring to JY / T010-1996. As an example, the following method can be used: arbitrarily select a test sample with a length × width of 10 mm × 10 mm on the negative electrode sheet, randomly select multiple test areas (e.g., 5) in the test sample, and read the particle size of the carbon-based material particles in each test area at a certain magnification (e.g., 20000 times) (i.e., take the distance between the two farthest points on the carbon-based material particle as the particle size), count the number and particle size values ​​of the carbon-based material particles in each test area, and take the arithmetic mean of the carbon-based material particles in each test area, which is the average particle size of the carbon-based material particles in the test sample. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be taken and the above test can be repeated. The average value of each test sample can be taken as the final test result.

[0088] In some embodiments, the average roughness Ra of the negative electrode current collector facing the negative electrode interface layer is 0.1-0.8 μm or 0.2-0.4 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.33 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any combination of the above values. Thus, on the one hand, limiting the upper limit of the average roughness is beneficial to improving the uniformity of the electric field distribution on the surface of the negative electrode current collector and suppressing the formation of lithium dendrites; on the other hand, limiting the lower limit of the average roughness is beneficial to improving the electrical contact between lithium and the negative electrode current collector during lithium deposition, while reducing the requirements for manufacturing processes and lowering production costs.

[0089] In this application, the average roughness Ra of the negative electrode current collector facing the negative electrode interface layer can be tested using conventional methods in the art. For example, the following specific method can be used: Referring to GB / T 1031-2009, using a contact roughness meter, select a test sample surface with a length × width of 50 mm × 20 mm. Within the sampling length (4 mm), take the absolute values ​​of all height differences on the surface, and calculate the arithmetic mean of these absolute values, which is the average roughness Ra. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be used to repeat the above test, and the average value of each test sample can be taken as the final test result.

[0090] Another embodiment of this application provides a method for preparing lithium metal battery cells, comprising the following steps:

[0091] The lithium metal battery cell includes at least one electrode assembly. A constant pressure is applied to opposite sides of the electrode assembly along its thickness direction, or to opposite sides of the lithium metal battery cell along the thickness direction of the electrode assembly, while simultaneously satisfying that the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88, for example, ≥0.90, ≥0.95, ≥1.00, ≥1.03, or any combination of the above values; wherein,

[0092] The electrode assembly includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; the negative electrode includes a negative current collector and a negative interface layer located on at least one side of the negative current collector, the negative interface layer being located between the negative current collector and the separator.

[0093] The cyclic thickness change of the electrode assembly is the average of the thickness change of the electrode assembly before and after each charge and the thickness change of the electrode assembly before and after each discharge in the charge-discharge cycle, in μm. The charge-discharge cycle is performed by charging to 4.3V with a constant current of 0.2C and then discharging to 2.8V with a constant current of 0.5C.

[0094] The theoretical lithium metal thickness variation of the electrode assembly is calculated according to the following formula:

[0095]

[0096] Where h represents the theoretical lithium metal thickness variation of the electrode assembly, in μm; Y represents the average charge and discharge capacity of the electrode assembly in each charge-discharge cycle, in Ah, wherein the charge-discharge cycle is performed by charging at a constant current of 0.2C to 4.3V and then discharging at a constant current of 0.5C to 2.8V; F represents the Faraday constant, in C / mol; M represents the molar mass of lithium, in g / mol; and ρ represents the density of lithium, in g / cm³. 3 A represents the area of ​​the overlap of the positive electrode, the separator, and the negative electrode in the electrode assembly, in cm². 2 .

[0097] Therefore, this application applies a constant pressure to opposite sides of the electrode assembly along the thickness direction or to opposite sides of the lithium metal battery cell along the thickness direction of the electrode assembly, and maintains the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change at ≥0.88. Under this constraint, as the amount of lithium metal deposited during battery cell charging increases, the increase in internal stress of the electrode assembly can be effectively suppressed, thereby preventing the deposited lithium metal from entering the negative electrode interface layer and damaging its structure, maintaining the integrity of the negative electrode interface layer structure, suppressing lithium dendrite growth, and thus improving the cycle performance and safety performance of the battery cell.

[0098] In some embodiments, the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is 0.88-1.35 or 0.95-1.03, for example, 0.88, 0.9, 1.0, 1.03, 1.1, 1.2, 1.3, 1.35 or any range of the above values.

[0099] In some embodiments, the constant pressure is 0.5MPa-2MPa or 1MPa-1.5MPa, for example, 0.5MPa, 0.8MPa, 1MPa, 1.2MPa, 1.5MPa, 1.7MPa, 2MPa or any range of the above values.

[0100] In some embodiments, the negative electrode interface layer is prepared by the following steps:

[0101] A negative electrode interface slurry is coated onto one or both sides of the negative electrode current collector facing the separator, and then dried and optionally cold-pressed to obtain a negative electrode interface layer located on at least one side of the negative electrode current collector.

[0102] In some embodiments, the compaction density of the negative electrode interface layer is 0.6 g / cm³. 3 -1.5g / cm 3 or 0.8g / cm 3 -1.2g / cm 3 For example, 0.6 g / cm³ 3 0.8g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.2g / cm 3 1.3g / cm 3 1.5g / cm 3 Or a range consisting of any of the above values.

[0103] In some embodiments, the negative electrode interface layer comprises carbon-based material particles with an average particle size of 1 nm-10 μm or 50 nm-1 μm, such as 1 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 700 nm, 800 nm, 1 μm, 2 μm, 3 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm or any combination of the above values.

[0104] In some embodiments, the average roughness Ra of the negative electrode current collector on the side facing the negative electrode interface layer is 0.1-0.8 μm or 0.2-0.4 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.33 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm or any range of the above values.

[0105] In some implementations, the lithium metal battery cell is a lithium metal battery cell without a negative electrode.

[0106] [Positive electrode plate]

[0107] In some embodiments, the positive electrode can be a positive electrode sheet, which may include a positive current collector and a positive active material disposed on at least one surface of the positive current collector.

[0108] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0109] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0110] In some embodiments, the battery cell is a lithium-ion battery (e.g., a lithium metal battery), and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion batteries. The positive electrode active material may include at least one of the following materials: lithium phosphates, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphates include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4, also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (e.g., LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., 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 LiNi 0.6 Co 0.2 Mn 0.2 O2, also known as NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2, also known as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.05 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0111] During the charging and discharging process, the battery will produce active ions (Li). +Due to the intercalation and deintercalation of Li, the molar content of Li varies when the battery is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Li will change after charge-discharge cycles.

[0112] In the examples of positive electrode active materials in this application, the molar content of oxygen is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of oxygen will fluctuate.

[0113] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0114] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0116] [Negative electrode plate]

[0117] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0118] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the carbon-based material in the negative electrode interface layer may be of a type known in the art. As an example, the carbon-based material may include at least one of the following: artificial graphite, natural graphite, soft carbon, hard carbon, etc. However, this application is not limited to these materials, and other conventional carbon-based materials may also be used. These carbon-based materials may be used alone or in combination of two or more.

[0120] In some embodiments, the negative electrode interface layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0121] In some embodiments, the negative electrode interface layer may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0122] In some embodiments, the negative electrode interface layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0123] In some implementations, the negative electrode interface layer and the negative electrode active layer serve different purposes. The main function of the negative electrode interface layer is to conduct lithium ions to the space between the negative electrode interface layer and the negative electrode current collector for deposition during battery cell charging, and to isolate the deposited lithium from the separator to reduce the risk of lithium dendrites puncturing the separator.

[0124] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode interface material (e.g., carbon-based material), conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode interface slurry; coating the negative electrode interface slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0125] [Electrolytes]

[0126] In some embodiments, the battery cell also includes an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, gel, or solid.

[0127] Liquid electrolytes include electrolyte salts and solvents.

[0128] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0129] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. The solvent may also be an ether solvent. Ether solvents may include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and crown ethers.

[0130] 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 additives that can improve certain properties of the battery cell, such as additives that improve the overcharge / fast charge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature performance of the battery cell.

[0131] The gel electrolyte includes a polymer as a backbone network and can be used in conjunction with an ionic liquid—lithium salt.

[0132] Solid electrolytes include polymer solid electrolytes, inorganic solid electrolytes, and composite solid electrolytes.

[0133] As an example, the polymers of polymeric solid electrolytes may include polyethers (polyoxyethylene), polysiloxanes, polycarbonates, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, monoionic polymers, polyionic liquids, cellulose, etc.

[0134] As an example, inorganic solid electrolytes can be one or more of the following: oxide solid electrolytes (crystalline perovskite, sodium superconducting ion conductor, garnet, amorphous LiPON thin film), sulfide solid electrolytes (crystalline lithium superconducting ion conductor (lithium-germanium-phosphorus-sulfur, sulfosilium-germanium), amorphous sulfides), halide solid electrolytes, nitride solid electrolytes, and hydride solid electrolytes.

[0135] As an example, composite solid electrolytes are formed by adding inorganic solid electrolyte fillers to polymer solid electrolytes.

[0136] [Isolation Component]

[0137] In some embodiments, the electrode assembly further includes an isolator disposed between the positive and negative electrodes.

[0138] In some embodiments, the separator is a separator membrane. This application does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0139] As an example, the main material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyimide porous membrane, polyvinylidene fluoride, and ceramic. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. 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 can also be applied to the surface of the separator.

[0140] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, serving both to transport ions and to isolate the positive and negative electrodes.

[0141] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0142] [Structure of the electrode assembly]

[0143] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0144] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0145] In some implementations, the electrode assembly is a stacked structure.

[0146] As an example, multiple positive and negative electrodes can be set, and multiple positive and multiple negative electrodes can be stacked alternately.

[0147] As an example, multiple positive electrode plates can be provided, and negative electrode plates can be folded to form multiple stacked folded segments, with a positive electrode plate sandwiched between adjacent folded segments.

[0148] As an example, both the positive and negative electrode plates are folded to form multiple stacked folded segments.

[0149] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0150] As an example, the separators can be continuously arranged, either by folding or rolling between any adjacent positive or negative electrode plates.

[0151] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0152] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0153] [shell]

[0154] In some embodiments, the battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0155] As an example, the battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0156] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also be provided one or more.

[0157] [Electrode terminals]

[0158] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0159] [Pressure relief mechanism]

[0160] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0161] As an example, the internal pressure or temperature of a battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is broken, thereby creating an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the battery cell.

[0162] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0163] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0164] The term "actuation" as used in this application refers to the activation or actuation of the pressure relief mechanism to a certain state, thereby releasing the internal pressure and temperature of the battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is activated, the high-temperature, high-pressure substances inside the battery cell are discharged as waste from the activated portion. This method allows for pressure and temperature relief of the battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0165] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for venting gas inside the battery cell.

[0166] The emissions from battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of separators, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0167] [Battery Device]

[0168] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells connected in series, parallel, or mixed connections via a busbar.

[0169] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells.

[0170] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0171] 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.

[0172] 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.

[0173] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple battery cells to the housing.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use individual battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0178] For example, Figure 4 The example shown is a square-structured battery cell 5.

[0179] In some implementations, refer to Figure 5The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0180] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0181] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0182] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0183] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0184] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0185] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0186] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0187] Figure 9 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0188] [Example]

[0189] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0190] Example 1

[0191] (1) Preparation of negative electrode sheet: Hard carbon (average particle size of 100nm) and binder polyvinylidene fluoride are mixed at a mass ratio of 9:1. N-methylpyrrolidone solvent is added and the mixture is continued to be mixed to obtain a slurry with a solid content of 20% by mass. The slurry is coated on one side of a copper foil with a thickness of 15μm and dried in a forced-air oven at 85℃ for 20 minutes. It is then cold-pressed at a pressure of 98kN and a roll gap of 30μm, and cut to obtain the negative electrode sheet.

[0192] (2) Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide, conductive carbon black and binder polyvinylidene fluoride are mixed in a mass ratio of 95:3:2 and then N-methylpyrrolidone solvent is added. The mixture is coated on one side of the positive electrode current collector aluminum foil, and after drying, cold pressing and cutting, the positive electrode sheet is obtained.

[0193] (3) Separation membrane: a polyethylene membrane with a thickness of 12μm.

[0194] (4) Preparation of electrolyte: Lithium bis(fluorosulfonyl)imide (LiFSI) solution with a molar concentration of 1 mol / L in dimethyl ether (DME).

[0195] (5) Assembly of lithium metal battery cells:

[0196] The electrode assembly is stacked in the order of negative electrode, separator, and positive electrode, placed in an aluminum-plastic film, and electrolyte is injected at an injection coefficient of 9 g / Ah, followed by vacuum sealing. A constant pressure of 1 MPa is applied to both sides of the lithium metal battery cell using a constant pressure fixture along the stacking direction of the negative electrode, separator, and positive electrode.

[0197] Battery cell testing

[0198] (1) Interfacial impedance test between the separator and the negative electrode interface layer of the battery cell:

[0199] Principle: The AC impedance spectroscopy method measures the current response by applying AC voltages of different frequencies to a single battery cell. The mid-frequency region reflects the interfacial impedance between the separator and the negative electrode interface layer. The test results are obtained by fitting the impedance spectrum through an equivalent circuit model.

[0200] Specific method: Connect the positive and negative electrodes of the battery cell that has not undergone charge-discharge cycles to an electrochemical impedance spectroscopy (e.g., VMP-300, Biologic) and measure the open-circuit voltage. Using the measured open-circuit voltage as the initial voltage, apply an excitation voltage with an amplitude of 10mV and test at a frequency range of 0.1Hz-1MHz. Plot the impedance data into a Nyquist plot. Based on the semicircle in the mid-frequency region (e.g., 1Hz-1kHz), use an equivalent circuit model to fit the plot and obtain the interfacial impedance value between the separator and the negative electrode interface layer.

[0201] At 25°C, charge the battery cell at a rate of 0.2C to 4.3V, then discharge it at a rate of 0.5C to 2.8V. Repeat this charge-discharge cycle for 30 cycles. Then test the interfacial impedance between the separator and the negative electrode interface layer using the method described above.

[0202] (2) Cycle capacity retention test of individual battery cells:

[0203] At 25°C, the battery cells are charged at a rate of 0.2C to a voltage of 4.3V, and then discharged at a rate of 0.5C to a voltage of 2.8V. This charge-discharge cycle is repeated. The cycle capacity retention rate is obtained by dividing the discharge capacity of the nth cycle by the discharge capacity of the first cycle. When the cycle capacity retention rate reaches 80%, the cycle number n is recorded.

[0204] (3) SEM testing of the negative electrode:

[0205] The negative electrode sheets of Example 1 and Comparative Example 2 were cut along the thickness direction using an ion beam. The cross-sections of the negative electrode sheets along the thickness direction of Example 1 and Comparative Example 2 were observed using a scanning electron microscope (e.g., ZEISS Sigma 300). The results are as follows: Figure 10-12 As shown.

[0206] Depend on Figure 10 As can be seen, in the negative electrode sheet of Embodiment 1 of this application, metallic lithium is deposited between the negative electrode current collector and the negative electrode interface layer, and there is basically no problem of metallic lithium entering the negative electrode interface layer. The structure of the negative electrode interface layer is intact and basically not damaged, which can effectively suppress the growth of lithium dendrites. However, due to Figure 11-12 It can be seen that in the negative electrode sheet of Comparative Example 2, the phenomenon of lithium metal entering the negative electrode interface layer has appeared. The negative electrode interface layer is broken and its structural integrity is destroyed under the action of lithium metal intrusion, which is not conducive to inhibiting the growth of lithium dendrites.

[0207] Examples 2-4 and Comparative Example 1

[0208] In Examples 2-4 and Comparative Example 1, a constant pressure fixture was used to apply constant pressures of 1.5 MPa, 2 MPa, 0.5 MPa, and 2.5 MPa to opposite sides of the lithium metal battery cell along the stacking direction of the negative electrode, separator, and positive electrode. The rest was the same as in Example 1.

[0209] Comparative Example 2

[0210] Along the stacking direction of the negative electrode, separator, and positive electrode, a constant-gap test fixture is used to apply an initial preload of 1 MPa to the opposite sides of the lithium metal battery cell. After that, the constant gap is maintained, and the rest is the same as in Example 1.

[0211] Some parameters of Examples 2-4 and Comparative Examples 1-2 are shown in Table 1, and the remaining parameters are the same as those of Example 1.

[0212] Table 1. Some parameters and test results of Examples 1-4 and Comparative Examples 1-2

[0213]

[0214] It can be seen from the above table:

[0215] Compared with the electrode assembly of Comparative Example 1, the ratio of the cycle thickness change to the theoretical lithium metal thickness change of the electrode assemblies in Examples 1-4 of this application is greater than or equal to 0.88, and the cycle performance of their lithium metal battery cells is significantly improved.

[0216] Compared with the constant-gap charge-discharge cycle mode of Comparative Example 2, the electrode components of Examples 1-4 of this application have constant pressure on opposite sides along the thickness direction, and the ratio of the cycle thickness change of the electrode component to the theoretical lithium metal thickness change is greater than or equal to 0.88. The density of lithium deposited on the negative electrode sheet of the electrode component is improved, the expansion of the battery cell is significantly suppressed, and the cycle performance of the lithium metal battery cell is significantly improved. Furthermore, after multiple cycles, the separator and the negative electrode interface layer of the battery cell still remain tightly bonded, which significantly suppresses the increase of the interface impedance between the separator and the negative electrode interface layer.

[0217] Compared to the smaller ratio of the electrode assembly cycling thickness change to the theoretical lithium metal thickness change in Example 3, the cycling performance of the lithium metal battery cells in Examples 1-2 of this application is significantly improved.

[0218] Compared to the larger ratio of the change in electrode assembly thickness during cycling to the theoretical change in lithium metal thickness in Example 4, the interfacial impedance between the separator and the negative electrode in the lithium metal battery cells of Examples 1-2 of this application is significantly lower and the cycling performance is significantly higher.

[0219] Examples 5-8

[0220] In Examples 5 and 7, by reducing the cold pressing pressure and increasing the roll gap width during the preparation of the negative electrode sheet, the compaction density of the negative electrode interface layer was reduced to 0.8 g / cm³, respectively. 3 0.6g / cm 3 The rest is the same as in Example 1.

[0221] In Examples 6 and 8, by increasing the cold pressing pressure and decreasing the roll gap width during the preparation of the negative electrode sheet, the compaction density of the negative electrode interface layer was increased to 1.2 g / cm³, respectively. 3 1.5g / cm 3 The rest is the same as in Example 1.

[0222] Some parameters of Examples 5-8 are shown in Table 2, and the remaining parameters are the same as those of Example 1.

[0223] Table 2. Some parameters and test results of Examples 1 and 5-8

[0224]

[0225]

[0226] It can be seen from the above table:

[0227] Compared with the lower compaction density of the negative electrode interface layer in Example 7, the lithium metal battery cells in Examples 1 and 5-6 of this application are better able to suppress the deposited lithium metal from entering the negative electrode interface layer and damaging its structure, thereby improving the cycle performance of the battery. Furthermore, there are more contact sites between the separator and the negative electrode interface layer, and the interfacial impedance between the separator and the negative electrode interface layer is significantly lower.

[0228] Compared with the higher compaction density of the negative electrode interface layer in Example 8, the lithium conduction performance of the negative electrode interface layer of the lithium metal battery cells in Examples 1 and 5-6 of this application is better, and the cycle performance is significantly improved.

[0229] Examples 9-12

[0230] By mechanical grinding, the average roughness Ra of the surface of the negative electrode current collector facing the negative electrode interface layer in Examples 9-12 was adjusted to 0.2, 0.4, 0.1 and 0.8 respectively, and the rest was the same as in Example 1.

[0231] Some parameters of Examples 9-12 are shown in Table 3, and the remaining parameters are the same as those of Example 1.

[0232] Table 3. Partial parameters and test results of Examples 1 and 9-12

[0233]

[0234] It can be seen from the above table:

[0235] Compared to Example 11, where the surface roughness of the negative electrode current collector facing the negative electrode interface layer is smaller, Examples 1 and 9-10 of this application have higher electrical contact with the negative electrode current collector during lithium deposition, resulting in significantly higher cycle performance of the battery cells.

[0236] Compared with the larger surface roughness of the negative electrode current collector on the side facing the negative electrode interface layer in Example 12, the electric field distribution of the negative electrode current collector in Examples 1 and 9-10 of this application is more uniform, which is beneficial to suppressing the growth of lithium dendrites and significantly improving the cycle performance of the battery cell.

[0237] Examples 13-16

[0238] The average particle sizes of the hard carbon used in Examples 13-16 were 50 nm, 1 μm, 1 nm, and 10 μm, respectively, and the rest were the same as in Example 1.

[0239] Some parameters of Examples 13-16 are shown in Table 4, and the rest are the same as those of Example 1.

[0240] Table 4. Partial parameters and test results of Examples 1 and 13-16

[0241]

[0242] *: Due to the limitations of the testing instrument's accuracy, only two decimal places are retained; the actual value is between 1.04 and 1.05.

[0243] #: Due to the limitations of the testing instrument's precision, only two decimal places are retained; the actual value is between 1.00 and 1.01.

[0244] It can be seen from the above table:

[0245] Compared with the use of hard carbon material with smaller average particle size in the negative electrode interface layer of Example 15, the lithium metal battery cells of Examples 1 and 13-14 of this application have better lithium conduction performance in the negative electrode interface layer and significantly improved cycle performance.

[0246] Compared with the use of hard carbon material with a larger average particle size in the negative electrode interface layer of Example 16, the lithium metal battery cells of Examples 1 and 13-14 of this application are better able to suppress the deposition of lithium metal into the negative electrode interface layer and destroy its structure, thus improving the cycle performance of the battery cells. Furthermore, they result in more contact sites between the separator and the negative electrode interface layer and significantly lower interfacial impedance between the separator and the negative electrode interface layer.

[0247] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium metal battery cell, comprising at least one electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; the negative electrode comprising a negative current collector and a negative interface layer located on at least one side of the negative current collector, the negative interface layer being located between the negative current collector and the separator; The electrode assembly has constant pressure on opposite sides along the thickness direction; The ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88; wherein, The cyclic thickness change of the electrode assembly is the average of the thickness change of the electrode assembly before and after each charge and the thickness change of the electrode assembly before and after each discharge in the charge-discharge cycle, in μm. The charge-discharge cycle is performed by charging to 4.3V with a constant current of 0.2C and then discharging to 2.8V with a constant current of 0.5C. The theoretical lithium metal thickness variation of the electrode assembly is calculated according to the following formula: Where h represents the theoretical lithium metal thickness variation of the electrode assembly, in μm; Y represents the average charge and discharge capacity of the electrode assembly in each charge-discharge cycle, in Ah, wherein the charge-discharge cycle is performed by charging at a constant current of 0.2C to 4.3V and then discharging at a constant current of 0.5C to 2.8V; F represents the Faraday constant, in C / mol; M represents the molar mass of lithium, in g / mol; and ρ represents the density of lithium, in g / cm³. 3 A represents the area of ​​the overlap of the positive electrode, the separator, and the negative electrode in the electrode assembly, in cm². 2 .

2. The lithium metal battery cell according to claim 1, wherein, The ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is 0.88-1.35 or 0.95-1.

03.

3. The lithium metal battery cell according to claim 1 or 2, wherein, The constant pressure is 0.5MPa-2MPa or 1MPa-1.5MPa.

4. The lithium metal battery cell according to any one of claims 1 to 3, wherein, The compaction density of the negative electrode interface layer is 0.6 g / cm³. 3 -1.5g / cm 3 or 0.8g / cm 3 -1.2g / cm 3 .

5. The lithium metal battery cell according to any one of claims 1 to 4, wherein, The negative electrode interface layer comprises carbon-based material particles, the average particle size of which is 1nm-10μm or 50nm-1μm.

6. The lithium metal battery cell according to any one of claims 1 to 5, wherein, The average roughness Ra of the negative electrode current collector on the side facing the negative electrode interface layer is 0.1-0.8 μm or 0.2-0.4 μm.

7. A method for preparing lithium metal battery cells, comprising the following steps: The lithium metal battery cell includes at least one electrode assembly. A constant pressure is applied to opposite sides of the electrode assembly along its thickness direction, or to opposite sides of the lithium metal battery cell along the thickness direction of the electrode assembly, while simultaneously satisfying that the ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is ≥0.88; wherein, The electrode assembly includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode; the negative electrode includes a negative current collector and a negative interface layer located on at least one side of the negative current collector, the negative interface layer being located between the negative current collector and the separator. The cyclic thickness change of the electrode assembly is the average of the thickness change of the electrode assembly before and after each charge and the thickness change of the electrode assembly before and after each discharge in the charge-discharge cycle, in μm. The charge-discharge cycle is performed by charging to 4.3V with a constant current of 0.2C and then discharging to 2.8V with a constant current of 0.5C. The theoretical lithium metal thickness variation of the electrode assembly is calculated according to the following formula: Where h represents the theoretical lithium metal thickness variation of the electrode assembly, in μm; Y represents the average charge and discharge capacity of the electrode assembly in each charge-discharge cycle, in Ah, wherein the charge-discharge cycle is performed by charging at a constant current of 0.2C to 4.3V and then discharging at a constant current of 0.5C to 2.8V; F represents the Faraday constant, in C / mol; M represents the molar mass of lithium, in g / mol; and ρ represents the density of lithium, in g / cm³. 3 A represents the area of ​​the overlap of the positive electrode, the separator, and the negative electrode in the electrode assembly, in cm². 2 .

8. The method according to claim 7, wherein, The ratio of the cyclic thickness change of the electrode assembly to the theoretical lithium metal thickness change is 0.88-1.35 or 0.95-1.

03.

9. The method according to claim 7 or 8, wherein, The constant pressure is 0.5MPa-2MPa or 1MPa-1.5MPa.

10. The method according to any one of claims 7 to 9, wherein, The negative electrode interface layer is prepared through the following steps: A negative electrode interface slurry is coated onto one or both sides of the negative electrode current collector facing the separator, and then dried and optionally cold-pressed to obtain the negative electrode interface layer located on at least one side of the negative electrode current collector.

11. The method according to any one of claims 7 to 10, wherein, The compaction density of the negative electrode interface layer is 0.6 g / cm³. 3 -1.5g / cm 3 or 0.8g / cm 3 -1.2g / cm 3 .

12. The method according to any one of claims 7 to 11, wherein, The negative electrode interface layer comprises carbon-based material particles, the average particle size of which is 1nm-10μm or 50nm-1μm.

13. The method according to any one of claims 7 to 12, wherein, The average roughness Ra of the negative electrode current collector on the side facing the negative electrode interface layer is 0.1-0.8 μm or 0.2-0.4 μm.

14. A battery device comprising a lithium metal battery cell according to any one of claims 1 to 6 or a lithium metal battery cell prepared by the method according to any one of claims 7 to 13.

15. An electrical device comprising a lithium metal battery cell according to any one of claims 1 to 6, a lithium metal battery cell prepared by the method according to any one of claims 7 to 13, or a battery device according to claim 14.

Images