Positive electrode sheet, battery cell, battery and electric device

Abstract

A positive electrode sheet, a battery cell, a battery and an electric device. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein a preset lithium salt is dispersed in the positive electrode film layer, and the preset lithium salt comprises a first lithium salt having a structure shown in formula 1, where R1 and R2 each independently comprises a fluorine atom or a C1-C6 fluoroalkyl group, and M1 is Li. The introduction of the preset lithium salt into the positive electrode sheet enables a battery cell using the positive electrode sheet to achieve good cycling performance.

Description

Positive electrode sheet, battery cell, battery and electrical device Technical Field

[0001] The present application relates to a positive electrode sheet, a battery cell, a battery and an electrical device. Background Art

[0002] Lithium-ion battery cells have been widely used in many fields such as consumer electronics, electric vehicles, and energy storage technology, but their energy density has approached the theoretical limit. In order to meet the demand for higher energy density in future high-endurance electric vehicles, electric aircraft, etc., it is necessary to develop battery cells using metal lithium negative electrodes. The electrolyte plays a vital role in the stable operation of battery cells. The electrolyte of lithium-ion battery cells widely uses ester solvents, but this electrolyte system is not suitable for battery cells using metal lithium negative electrodes. In addition, during the cyclic charge and discharge process, the volume change of the negative electrode of the lithium-ion battery is relatively small, and the mechanical strength requirements of the solid electrolyte interface film (hereinafter referred to as SEI film) formed on the surface of the negative electrode are not high; however, the metal lithium negative electrode is very active and will spontaneously react with the electrolyte to form an SEI film with poor mechanical strength and chemical stability. It will also cause the dendritic growth morphology of the metal lithium negative electrode, thereby causing the cycle life of the battery cell using the metal lithium negative electrode to quickly deteriorate. The above statements are only used to provide background technical information related to this application and do not necessarily constitute prior art.

[0003] Summary of the Invention

[0004] The present application provides a positive electrode plate, a battery cell, a battery and an electrical device, which can enable the battery to have good cycle performance.

[0005] In a first aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein a predetermined lithium salt is dispersed in the positive electrode film layer, and the predetermined lithium salt comprises a first lithium salt having a structure shown in Formula 1, R1 and R2 each independently comprise a fluorine atom or a C1-C6 fluoroalkyl group, M1 is Li,

[0006] As the electrolyte salt is consumed during the battery cell cycle, the electrolyte concentration continues to decrease. The preset lithium salt in the positive electrode sheet can slowly dissolve into the electrolyte, thereby maintaining a high concentration of the electrolyte during the battery cell cycle. This can maintain the solvation structure of the initially designed high-concentration electrolyte during the battery cell cycle, allowing the electrolyte to maintain high redox resistance, thereby improving the cycle performance of the battery cell. In addition, the preset lithium salt in the positive electrode sheet can also serve as a positive electrode additive to improve the quality of the positive electrode film formation and alleviate gas production problems, thereby also improving the high-temperature performance of the battery cell.

[0007] In some embodiments, R1 and R2 each independently include a fluorine atom or a trifluoromethyl group.

[0008] In some embodiments, the mass percentage of the first lithium salt in the positive electrode film layer is 0.8 wt %-10 wt %, and can be optionally 2 wt %-6.5 wt %.

[0009] In some embodiments, the preset lithium salt further includes a second lithium salt, and the second lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0010] Optionally, the second lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0011] In some embodiments, the molar ratio of the second lithium salt to the first lithium salt is 0.02:1-0.2:1, optionally 0.02:1-0.1:1.

[0012] An appropriate amount of the second lithium salt can further regulate the solvation structure and promote the desolvation process without significantly affecting the energy density of the battery cell, thereby enabling the battery cell to have better cycle performance.

[0013] In some embodiments, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium transition metal oxides, lithium-containing phosphates, and modified compounds thereof.

[0014] In a second aspect, the present application provides a battery cell comprising the positive electrode sheet according to the first aspect of the present application.

[0015] In some embodiments, the battery cell includes an electrolyte, the electrolyte includes an electrolyte salt and a solvent, the electrolyte salt includes a main lithium salt, the main lithium salt includes a first lithium salt having a structure shown in Formula 1, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, M1 is Li,

[0016] In some embodiments, the sum of the mass of the first lithium salt in the positive electrode film layer and the mass of the first lithium salt in the electrolyte is greater than the saturated solubility of the first lithium salt in the electrolyte.

[0017] The sum of the mass of the first lithium salt in the positive electrode film layer and the mass of the first lithium salt in the electrolyte is greater than the saturated solubility of the first lithium salt in the electrolyte. During the cycle of the battery cell, the first lithium salt in the electrolyte is continuously consumed, and the first lithium salt in the positive electrode film layer can be slowly dissolved into the electrolyte under the infiltration of the electrolyte, thereby maintaining a high concentration of the electrolyte during the cycle of the battery cell, thereby maintaining the solvation structure of the initially designed high-concentration electrolyte during the cycle of the battery cell, and maintaining high redox resistance of the electrolyte, thereby enabling the battery cell to have good cycle performance.

[0018] In some embodiments, the solvent includes an ether compound. Ether compound solvents are more friendly to the metallic lithium negative electrode.

[0019] In some embodiments, the solvent includes one or more of methyl n-butyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,2-dimethoxypropane, 1,3-dimethoxypropane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0020] In some embodiments, the molar ratio of the main lithium salt to the solvent in the electrolyte is 1:0.8-1:3, and can be optionally 1:1-1:2.

[0021] The main lithium salt has a wider electrochemical window, higher thermal stability and higher ionic conductivity, which can provide less high-voltage decomposition of the electrolyte and faster ion transmission speed; the high concentration of the main lithium salt can make the lithium ions in the electrolyte have a good solvation structure, so that the electrolyte has good redox resistance, and thus can make the battery cell have better cycle performance.

[0022] In some embodiments, the electrolyte salt further includes an auxiliary lithium salt, and the auxiliary lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0023] In some embodiments, the molar ratio of the auxiliary lithium salt to the main lithium salt in the electrolyte is 0.02:1-0.2:1, and can be optionally 0.05:1-0.1:1.

[0024] A small amount of auxiliary lithium salt can regulate the solvation structure and promote the desolvation process. If the concentration of auxiliary lithium salt is too high, it will significantly reduce the solubility of the main lithium salt. Therefore, when the concentration of auxiliary lithium salt in the electrolyte is within the above range, the battery cell can have better cycling performance.

[0025] In some embodiments, the electrolyte further includes a diluent, and the molar ratio of the main lithium salt to the diluent in the electrolyte is 1:0.5-1:5.

[0026] After the diluent is added, it will not affect the unique solvation structure of the original high-concentration electrolyte, and can improve the conductivity of the electrolyte.

[0027] In some embodiments, the diluent includes one or more of a fluoroether diluent, an aromatic diluent, and a fluorinated aromatic diluent.

[0028] In some embodiments, the diluent includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl, 1-(1,1,2,2-tetrafluoroethoxy)propane, 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 2 , 2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ester, bis-(1,2,2,2-tetrafluoroethyl) ether, 1,1,2,3,3,3-pentafluoropropyl difluoromethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, benzene, 3-fluorobenzene, m-difluorobenzene, 1,3,5-trifluorobenzene, and one or more of anisole.

[0029] In some embodiments, the battery cell is a lithium metal battery cell or a negative electrode-free lithium metal battery cell.

[0030] In a third aspect, the present application provides a battery comprising the battery cell according to the second aspect of the present application.

[0031] In a fourth aspect, the present application provides an electrical device comprising the battery according to the third aspect of the present application, wherein the battery is used to provide electrical energy.

[0032] The electric device of the present application includes the battery provided by the present application, and thus has at least the same advantages as the battery.

[0033] This application provides a preset lithium salt in the positive electrode plate. As the electrolyte salt is continuously consumed during the battery cell cycle, the concentration of the electrolyte continues to decrease. The preset lithium salt in the positive electrode plate can slowly dissolve into the electrolyte, thereby maintaining a high concentration of the electrolyte during the battery cell cycle. This can also maintain the solvation structure of the initially designed high-concentration electrolyte during the battery cell cycle, allowing the electrolyte to maintain high redox resistance, thereby improving the cycle performance of the battery cell. In addition, the preset lithium salt in the positive electrode plate can also serve as a positive electrode additive to improve the quality of the positive electrode film formation and alleviate gas production problems, thereby also improving the high-temperature performance of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0035] FIG1 is a schematic diagram of a battery cell provided by some embodiments of the present application.

[0036] FIG2 shows an exploded schematic diagram of a battery cell provided in some embodiments of the present application.

[0037] FIG3 shows a schematic diagram of a battery module provided in some embodiments of the present application.

[0038] FIG4 shows a schematic diagram of a battery pack provided in some embodiments of the present application.

[0039] FIG5 is an exploded schematic diagram of the battery pack shown in FIG4 .

[0040] FIG6 shows a schematic diagram of an electrical device provided in some embodiments of the present application.

[0041] In the accompanying drawings, the drawings are not necessarily drawn to scale.

[0042] The description of the accompanying figures is as follows: 1. battery pack; 2. upper box; 3. lower box; 4. battery module; 5. battery cell; 51. shell; 52. electrode assembly; 53. cover plate. DETAILED DESCRIPTION

[0043] Below, the embodiments of the positive electrode sheet, battery cell, battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0044] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0046] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0047] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0048] In this application, the terms "plurality" and "multiple" refer to two or more.

[0049] In the description of the embodiments of the present application, unless otherwise specified, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, a first feature being "above," "above," and "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. A first feature being "below," "below," and "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0050] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0051] Unless otherwise stated, the numerical values ​​of the various parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise stated, the test temperature of each parameter is 25°C.

[0052] The battery mentioned in the embodiments of the present application may be a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in the present application may include a battery cell, a battery module, or a battery pack.

[0053] A battery cell is the smallest unit of a battery, independently capable of charging and discharging. A battery cell can be cylindrical, rectangular, or have other shapes, though this is not a limitation in the present invention. Figure 1 shows a battery cell 5 with a rectangular structure as an example.

[0054] When there are multiple battery cells, the multiple battery cells are connected in series, in parallel, or in mixed series via a busbar. In some embodiments, the battery may be a battery module; when there are multiple battery cells, the multiple battery cells are arranged and fixed to form a battery module. In some embodiments, the battery may be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed in the housing. In some embodiments, the housing may serve as part of the vehicle's chassis structure. For example, a portion of the housing may form at least a portion of the vehicle's floor, or a portion of the housing may form at least a portion of the vehicle's crossbeam or longitudinal beam.

[0055] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 2 is a schematic diagram of a battery module 4 as an example. As shown in Figure 2, in the battery module 4, multiple battery cells 5 can be arranged in sequence along the length of the battery module 4. Of course, they can also be arranged in any other manner. The multiple battery cells 5 can further be fixed by fasteners.

[0056] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0057] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0058] Figures 3 and 4 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 3 and 4, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing comprises an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 may be arranged in any manner within the housing.

[0059] In some embodiments, the battery may be an energy storage device, including an energy storage container, an energy storage cabinet, and the like.

[0060] The battery cells provided in the embodiments of the present application may include lithium metal battery cells or negative electrode-free lithium metal battery cells.

[0061] A negative electrode-free lithium metal battery cell generally refers to a battery cell constructed without the active negative electrode layer being applied during the manufacturing process. For example, a negative electrode active material layer is not applied to the negative electrode through coating or deposition, or a carbonaceous active material layer is used to form the negative electrode active material layer. During initial charging, lithium ions gain electrons at the negative electrode and deposit on the surface of the negative electrode current collector, forming lithium metal. During discharge, the lithium metal is converted into lithium ions and returned to the positive electrode, enabling cyclic charge and discharge. Therefore, a negative electrode-free lithium metal battery cell can be considered a battery cell using metallic lithium as a negative electrode. Compared to other battery cells, a negative electrode-free lithium metal battery cell lacks a negative electrode active material layer, resulting in a higher energy density. In some embodiments, to improve battery cell performance, the negative electrode of a negative electrode-free lithium metal battery cell may also be coated with conventional negative electrode active materials, such as carbon materials. Although these materials have a certain capacity, their low content and their non-primary negative electrode active material in the battery cell mean that such a battery cell can still be considered a negative electrode-free lithium metal battery cell. The CB (Cell Balance) value of a negative electrode-free lithium metal battery cell is typically very small. For example, in some embodiments, the CB value of a negative electrode-free lithium metal battery cell can be less than or equal to 0.1. The CB value is the unit area capacity of the negative electrode in the battery cell divided by the unit area capacity of the positive electrode. Because a negative electrode-free lithium metal battery cell contains no or only a small amount of negative electrode active material, the unit area capacity of the negative electrode is small, and thus the CB value is very small, for example, typically less than or equal to 0.1.

[0062] The battery cell includes an electrode assembly, which may be a wound structure or a laminated structure, and the present invention is not limited thereto.

[0063] The battery cell may also include an outer packaging that can be used to encapsulate the electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging can also be a soft shell, such as a bag-type soft shell. The soft shell material can be plastic, such as one or more of aluminum-plastic film, polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0064] In some embodiments, as shown in Figure 5, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening, thereby sealing the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and can be adjusted according to needs.

[0065] To address the issues faced by battery cells using lithium metal anodes, high-concentration electrolytes (HCEs) are currently commonly used in conjunction with lithium metal anodes. Due to their unique solvation structure, HCEs offer excellent redox resistance and are more compatible with high-voltage cathode active materials.

[0066] Furthermore, during the lithium deposition and stripping process of the battery cells, the SEI film is constantly damaged and regenerated. This process primarily consumes electrolyte salts rather than solvents, causing the electrolyte concentration to continuously decrease during the battery cell cycle. This makes it difficult to maintain the initial high-concentration electrolyte solvation structure, which in turn causes the electrolyte's redox resistance to decline rapidly during the battery cell cycle. Consequently, the battery cell cycle life cannot meet higher usage requirements. A higher initial electrolyte concentration is more conducive to maintaining the solvation structure of the high-concentration electrolyte. However, the concentration of the high-concentration electrolyte has already reached its limit, and it is currently difficult to maintain this solvation structure by further increasing the electrolyte concentration.

[0067] In view of this, the present application starts from the perspective of the positive electrode sheet and, by setting a preset lithium salt in the positive electrode sheet, the battery cell using the positive electrode sheet can have good cycle performance.

[0068] An embodiment of the present application provides a positive electrode plate.

[0069] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. A preset lithium salt is dispersed in the positive electrode film layer. The preset lithium salt includes a first lithium salt having a structure shown in Formula 1, R1 and R2 independently include a fluorine atom or a C1-C6 fluoroalkyl group, and M1 is Li.

[0070] As the electrolyte salt is consumed during the battery cell cycle, the electrolyte concentration continues to decrease. The preset lithium salt in the positive electrode sheet can slowly dissolve into the electrolyte, thereby maintaining a high concentration of the electrolyte during the battery cell cycle. This can maintain the solvation structure of the initially designed high-concentration electrolyte during the battery cell cycle, allowing the electrolyte to maintain high redox resistance, thereby improving the cycle performance of the battery cell. In addition, the preset lithium salt in the positive electrode sheet can also serve as a positive electrode additive to improve the quality of the positive electrode film formation and alleviate gas production problems, thereby also improving the high-temperature performance of the battery cell.

[0071] R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group. A C1-C6 fluoroalkyl group means that at least one hydrogen atom in the C1-C6 alkyl group is replaced by a fluorine atom, or all hydrogen atoms are replaced by fluorine atoms, and can be, for example, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, or the like.

[0072] Optionally, R1 and R2 each independently include a fluorine atom or a trifluoromethyl group. More preferably, R1 and R2 are both fluorine atoms.

[0073] Alternatively, the first lithium salt may include one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), or a combination thereof.

[0074] More alternatively, the first lithium salt may include lithium bis(fluorosulfonyl)imide (LiFSI).

[0075] In the positive electrode sheet provided in the embodiment of the present application, the preset lithium salt is dispersed in the positive electrode film layer, for example, the preset lithium salt can be dispersed between the positive electrode active material particles.

[0076] The preset lithium salt is dispersed in the positive electrode film layer, which is conducive to the uniform diffusion of the preset lithium salt into the electrolyte during the battery cell cycle, so that the electrolyte maintains a high concentration during the battery cell cycle, thereby maintaining the solvation structure of the initially designed high-concentration electrolyte during the battery cell cycle, so that the electrolyte maintains high redox resistance, and thus can improve the cycle performance of the battery cell.

[0077] In some embodiments, the preset lithium salt can be evenly distributed along the thickness direction of the positive electrode film layer, that is, the content of the preset lithium salt can be equal; in some alternative embodiments, the content of the preset lithium salt can be gradient distributed along the thickness direction of the positive electrode film layer, for example, the content of the preset lithium salt at the surface position of the positive electrode film layer can be higher.

[0078] In some embodiments, the mass proportion of the first lithium salt in the positive electrode film layer can be 0.8wt%-10wt%, for example, it can be 0.8wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, or a range consisting of any of the above values.

[0079] The increase in the mass proportion of the first lithium salt in the positive electrode film layer is beneficial to maintaining the solvation structure of the initially designed high-concentration electrolyte during the battery cell cycle; however, if the mass proportion of the first lithium salt in the positive electrode film layer is too high, on the one hand, it will reduce the energy density of the battery cell, and on the other hand, it may also hinder the transmission of the electrolyte.

[0080] The mass proportion of the first lithium salt in the positive electrode film layer is within the above range. Under the premise of not significantly affecting the energy density of the battery cell, the solvation structure of the initially designed high-concentration electrolyte can be better maintained during the battery cell cycle process, so that the electrolyte maintains high redox resistance, thereby enabling the battery cell to have better cycle performance.

[0081] Optionally, the mass proportion of the first lithium salt in the positive electrode film layer may be 2 wt %-6.5 wt %.

[0082] In some embodiments, the predetermined lithium salt may further include a second lithium salt.

[0083] The second lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiOTf), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFBOP), and lithium tetrafluorooxalatophosphate (LiOTFP).

[0084] The second lithium salt in the positive electrode can further regulate the solvation structure and promote the desolvation process, thereby further improving the cycle performance of the battery cell.

[0085] Alternatively, the second lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium difluorophosphate (LiPO2F2).

[0086] Alternatively, the molar ratio of the second lithium salt to the first lithium salt may be 0.02:1-0.2:1, such as 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1, 0.2:1, or any range thereof. Alternatively, the molar ratio of the second lithium salt to the first lithium salt may be 0.02:1-0.15:1, 0.05:1-0.15:1, 0.02:1-0.1:1, or 0.05:1-0.1:1.

[0087] An appropriate amount of the second lithium salt can further regulate the solvation structure and promote the desolvation process without significantly affecting the energy density of the battery cell, thereby enabling the battery cell to have better cycle performance.

[0088] The mass proportion of the first lithium salt, the mass proportion of the second lithium salt, and the molar ratio of the second lithium salt to the first lithium salt in the positive electrode film layer can be tested as follows: the positive electrode plate is disassembled from the battery cell, and then the positive electrode plate is soaked in a known mass of ethylene glycol dimethyl ether (DME) for a period of time. The positive electrode plate is removed and the mass of the ethylene glycol dimethyl ether is weighed again. The difference between the two weighings is the mass of the preset lithium salt. An appropriate amount of the soaked liquid is taken and the mass content of the first lithium salt and the second lithium salt is tested by ion chromatography (IC). From this, the mass proportion of the first lithium salt and the mass proportion of the second lithium salt in the positive electrode film layer, as well as the molar ratio of the second lithium salt to the first lithium salt, can be calculated.

[0089] In the above tests, the battery cells refer to fresh battery cells, such as those that have been shipped from the factory or have been cycled no more than 50 times. If the battery cells have been cycled many times, a large amount of the preset lithium salt in the positive electrode film may have been dissolved, which will cause significant deviations in the test results.

[0090] The positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is arranged on either one or both of the two opposite surfaces of the positive electrode current collector.

[0091] In some embodiments, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates, and modified compounds thereof.

[0092] Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. The lithium transition metal oxides may include, but are not limited to, layered structures and spinel structures.

[0093] Examples of lithium-containing phosphates may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, a composite material of lithium iron manganese phosphate and carbon, and modified compounds thereof.

[0094] In some embodiments, in order to further improve the energy density of the battery cell, the positive electrode active material may include a general formula of Li a Ni b Co c M d O e D fOne or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M may include but is not limited to one or more of Ge, Mo, Sn, Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and D may include but is not limited to one or more of N, F, S and Cl.

[0095] As an example, the positive electrode active material may include but is not limited to LiCoO2, LiNiO2, LiMnO2, LiNi 1 / 2 Mn 1 / 2 O2、LiMn2O4、Li 4 / 3 Ti 5 / 3 O4、LiNi 1 / 2 Mn 1 / 2 O2、LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.80 Co 0.15 Al 0.05 One or more of O2, LiFePO4.

[0096] The charge and discharge process of a battery cell is accompanied by the intercalation and deintercalation of Li, and the molar content of Li in the battery cell varies at different discharge states. The molar content of Li in the examples of this application regarding the positive electrode active materials refers to the initial state of the material, i.e., the state before the materials are added. The molar content of Li in the positive electrode active materials used in the battery cell may change after charge and discharge cycles.

[0097] In the examples of the present application regarding the positive electrode active materials, the molar content of O is only a theoretical value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0098] The modified compounds of the above-mentioned positive electrode active materials may be used to perform doping modification and / or surface coating modification on the positive electrode active materials.

[0099] In some embodiments, the positive electrode film layer may further optionally 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.

[0100] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. As an example, the positive electrode binder may include, but is not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene oxide, fluorinated acrylic resin, styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and one or more of carboxymethyl chitosan (CMCS).

[0101] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include but is not limited to one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0102] The embodiments of the present application also provide a method for preparing a positive electrode sheet.

[0103] In some embodiments, the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, and the preset lithium salt can be dispersed in a solvent in a predetermined proportion and stirred evenly to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode current collector, and the positive electrode sheet with the preset lithium salt is obtained by drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto. The solid content of the positive electrode slurry can be 50%-80%. The introduction of the preset lithium salt during the preparation of the positive electrode slurry can make the distribution of the preset lithium salt in the positive electrode film layer more uniform, thereby facilitating the uniform diffusion of the preset lithium salt into the electrolyte, and thus making the battery cell have better cycle performance.

[0104] In some alternative embodiments, the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be dispersed in a solvent in a predetermined proportion and stirred evenly to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode current collector and dried to obtain a positive electrode sheet; a solution containing a preset lithium salt is coated on the surface of the positive electrode sheet, and after sufficient impregnation, it is transferred to an oven for further drying, and then cold pressed to obtain a positive electrode sheet with a preset lithium salt. The solvent in the positive electrode slurry can be N-methylpyrrolidone (NMP), but is not limited thereto. The solid content of the positive electrode slurry can be 60%-80%. The concentration of the solution containing the preset lithium salt can be 0.1 mol / L-3 mol / L, and the solvent can include one or more of N-methylpyrrolidone, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

[0105] In some alternative embodiments, the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be dispersed in a solvent in a predetermined proportion and stirred evenly to obtain a positive electrode slurry, and then the positive electrode slurry is coated on the positive electrode current collector, dried, and cold pressed to obtain a positive electrode sheet; a solution containing a preset lithium salt is coated on the surface of the positive electrode sheet, fully impregnated, and then transferred to an oven for further drying to obtain a positive electrode sheet with a preset lithium salt. The solvent in the positive electrode slurry can be N-methylpyrrolidone (NMP), but is not limited thereto. The solid content of the positive electrode slurry can be 60%-80%. The concentration of the solution containing the preset lithium salt can be 0.1 mol / L-3 mol / L, and the solvent can include one or more of N-methylpyrrolidone, ethylene glycol dimethyl ether, and ethylene glycol diethyl ether.

[0106] The embodiment of the present application further provides a battery cell, which includes the positive electrode plate with a preset lithium salt provided in the embodiment of the present application, thereby the battery cell provided in the embodiment of the present application can have a longer cycle life.

[0107] The battery cell provided in the embodiment of the present application may be a lithium metal battery cell or a negative electrode-free lithium metal battery cell.

[0108] The battery cell includes an electrolyte solution, which includes an electrolyte salt and a solvent.

[0109] The electrolyte salt includes a main lithium salt, the main lithium salt includes a first lithium salt having a structure shown in Formula 1, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, and M1 is Li.

[0110] The electrolyte includes a first lithium salt, which is a main lithium salt and can form a high-concentration electrolyte, thereby making the electrolyte have a good solvation structure and good redox resistance, thereby making the battery cell have good cycle performance.

[0111] The first lithium salt has a wider electrochemical window, higher thermal stability and higher ionic conductivity, thereby also providing less high-voltage decomposition of the electrolyte and faster ion transport speed.

[0112] In some embodiments, the sum of the mass of the first lithium salt in the positive electrode film layer and the mass of the first lithium salt in the electrolyte may be greater than the saturated solubility of the first lithium salt in the electrolyte.

[0113] The sum of the mass of the first lithium salt in the positive electrode film layer and the mass of the first lithium salt in the electrolyte is greater than the saturated solubility of the first lithium salt in the electrolyte. During the cycle of the battery cell, the first lithium salt in the electrolyte is continuously consumed, and the first lithium salt in the positive electrode film layer can be slowly dissolved into the electrolyte under the infiltration of the electrolyte, thereby maintaining a high concentration of the electrolyte during the cycle of the battery cell, thereby maintaining the solvation structure of the initially designed high-concentration electrolyte during the cycle of the battery cell, and maintaining high redox resistance of the electrolyte, thereby enabling the battery cell to have good cycle performance.

[0114] The electrolyte includes a solvent. In some embodiments, the solvent may include an ether compound. This is because ether compound solvents are more friendly to the metallic lithium negative electrode.

[0115] Alternatively, the solvent may include one or more of methyl n-butyl ether (MBE), tetrahydrofuran (THF), ethylene glycol dimethyl ether (DME), tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol diethyl ether (DEE), 1,2-dimethoxypropane (DMP1), 1,3-dimethoxypropane (DMP2), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0116] In some embodiments, the molar ratio of the main lithium salt to the solvent in the electrolyte can be 1:0.8-1:3, for example, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, or any range thereof. Alternatively, the molar ratio of the main lithium salt to the solvent in the electrolyte can be 1:1-1:2.

[0117] The main lithium salt has a wider electrochemical window, higher thermal stability and higher ionic conductivity, which can provide less high-voltage decomposition of the electrolyte and faster ion transmission speed; the high concentration of the main lithium salt can make the lithium ions in the electrolyte have a good solvation structure, so that the electrolyte has good redox resistance, and thus can make the battery cell have better cycle performance.

[0118] In some embodiments, the electrolyte salt may further include an auxiliary lithium salt. Optionally, the auxiliary lithium salt may include, but is not limited to, one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate, and may optionally include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0119] In some embodiments, the molar ratio of the auxiliary lithium salt to the main lithium salt in the electrolyte can be 0.02:1-0.2:1, for example, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.12:1, 0.14:1, 0.16:1, 0.18:1, 0.2:1, or any range thereof. Alternatively, the molar ratio of the auxiliary lithium salt to the main lithium salt in the electrolyte can be 0.02:1-0.1:1, or 0.05:1-0.1:1.

[0120] A small amount of auxiliary lithium salt can regulate the solvation structure and promote the desolvation process. Therefore, when the concentration of auxiliary lithium salt in the electrolyte is within the above range, the battery cell can have better cycle performance.

[0121] In some embodiments, the electrolyte may also include a diluent, thereby forming a localized high-concentration electrolyte (LHCE). A localized high-concentration electrolyte is a high-concentration electrolyte with the addition of a diluent that is miscible with the solvent but has poor solubility for electrolyte salts. The addition of the diluent does not affect the unique solvation structure of the original high-concentration electrolyte and can improve the viscosity and conductivity of the electrolyte.

[0122] Optionally, the diluent may include one or more of fluoroether diluents, aromatic diluents, and fluorinated aromatic diluents.

[0123] More optionally, the diluent may include, but is not limited to, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl (TFE), 1-(1,1,2,2-tetrafluoroethoxy)propane (TFEPE), 1,1,2,2-tetrafluoroethyl ethyl ether (ETE), bis(2,2,2-trifluoroethyl) ether (BTFE), difluoromethyl 2,2,3,3-tetrafluoropropyl ether, heptafluoropropyl 1, One or more of 2,2,2-tetrafluoroethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ester, bis-(1,2,2,2-tetrafluoroethyl) ether, 1,1,2,3,3,3-pentafluoropropyl difluoromethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, benzene (BZ), 3-fluorobenzene, m-difluorobenzene, 1,3,5-trifluorobenzene, and anisole.

[0124] In some embodiments, the molar ratio of the main lithium salt to the diluent in the electrolyte can be 1:0.5-1:5, for example, 1:0.5, 1:0.8, 1:1, 1:1.3, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or a range consisting of any of the above values.

[0125] The amount of diluent used will vary depending on the type of diluent and the content of electrolyte salt.

[0126] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives that can improve certain properties of the battery cell, such as additives that improve the overcharge performance of the battery cell, additives that improve the high-temperature performance of the battery cell, and additives that improve the low-temperature power performance of the battery cell.

[0127] In some embodiments, the viscosity of the electrolyte at 25° C. may be 2 mPa·s to 50 mPa·s, or optionally 3 mPa·s to 15 mPa·s, thereby helping the battery cell to have a long cycle life.

[0128] The viscosity of the electrolyte can be measured using a viscometer. The shear force applied to the rotor as it rotates continuously at a constant speed in the sample causes the spring to generate torque, which is proportional to the viscosity, thus providing the viscosity value of the sample.

[0129] For example, the viscosity of an electrolyte can be tested as follows: Under ambient humidity conditions of <80%, take a 30mL sample and place it in a water bath at 25°C for at least 30 minutes. Place a spindle (e.g., No. 18) in the sample cup and add the sample to a point approximately 0.3cm from the cup opening. Start the connected viscometer and rotate at 70 RPM for 5 minutes before reading the viscosity value. Ten data points can be collected and averaged during the test. The test instrument can be a Brookfield DV-2TLV viscometer.

[0130] In some embodiments, the conductivity of the electrolyte at 25° C. may be 1 mS / cm-15 mS / cm, optionally 3 mS / cm-8 mS / cm.

[0131] The conductivity of the electrolyte can be measured using a conductivity meter. For example, an appropriate amount of electrolyte can be taken and divided into three equal parts. The conductivity of each sample is then measured at 25°C using a conductivity meter. The average of the test results is then taken as the conductivity of the electrolyte. The measuring instrument can be a DDS-307 conductivity meter.

[0132] The electrolyte can be prepared by methods known in the art.

[0133] In some embodiments, a battery cell includes a negative electrode plate, which includes a negative electrode current collector and a lithium metal layer located on at least one side of the negative electrode current collector, thereby assembling a lithium metal battery cell. The lithium metal layer includes lithium metal or an alloy of lithium metal and other metal elements and / or non-metal elements. Other metal elements may include one or more of Sn, Zn, Al, Mg, Ag, Au, Ga, In, and Pt. Non-metal elements may include one or more of B, C, and Si.

[0134] In some embodiments, the negative electrode plate may include a negative electrode current collector but not a lithium metal layer, thereby assembling a negative electrode-free lithium metal battery cell. Optionally, the surface of the negative electrode current collector of the negative electrode-free lithium metal battery cell may also be provided with a modification layer capable of improving the lithium metal deposition behavior, for example, the modification layer may include a lithiophilic material.

[0135] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. As examples of metal foils, copper foil, copper alloy foil, nickel foil, and nickel alloy foil may be used. As examples of three-dimensional porous current collectors, copper mesh, nickel mesh, foam copper, and foam nickel may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include, but is not limited to, one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0136] The battery cell also includes a separator. The separator is located between the positive electrode and the negative electrode, and its main function is to prevent internal short circuits. The present application does not particularly limit the type of separator, and any well-known porous structure separator with good chemical and mechanical stability can be selected. In some embodiments, the material of the separator may include but is not limited to one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, polyimide and polyvinylidene fluoride. 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 are the same or different.

[0137] The charge and discharge rate of the battery cell provided in the embodiment of the present application can be between 0.01C and 8C.

[0138] The ambient temperature for recycling the battery cells provided in the embodiments of the present application may be between -30°C and 60°C.

[0139] The preparation method of battery cells is well known. In some embodiments, the positive electrode sheet, separator, negative electrode sheet and electrolyte can be assembled to form a battery cell. As an example, the positive electrode sheet, separator, and negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process. The electrode assembly is placed in an outer package, dried, and then injected with the above-mentioned electrolyte. After vacuum packaging, standing, and other processes, a battery cell is obtained. Multiple battery cells can also be further connected in series, in parallel, or in a mixed connection to form a battery module. Multiple battery modules can also be connected in series, in parallel, or in a mixed connection to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0140] The present application also provides an electrical device, which includes a battery provided in the present application. The battery can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0141] The electrical device can select the type of battery according to its usage requirements, such as a battery cell, a battery module or a battery pack.

[0142] Figure 6 is a schematic diagram of an exemplary electric device. This device is 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 this device, a battery pack or battery module may be used.

[0143] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0144] Example

[0145] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0146] Example 1

[0147] (1) Preparation of positive electrode sheet

[0148] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1O2, positive electrode conductive agent acetylene black, positive electrode binder polyvinylidene fluoride, and the first lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) are mixed in a mass ratio of 100:1:1:1, and the solvent N-methylpyrrolidone is added and stirred evenly to obtain a positive electrode slurry with a solid content of about 50%. The positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature (about 25°C), and then transferred to an oven for further drying, and then cold pressed to obtain a positive electrode sheet with a preset lithium salt. The positive electrode sheet is cut into a 40mm×50mm rectangle for standby use. The capacity of a single side of the positive electrode is 3.5mAh / cm 2 Up to 5mAh / cm 2 between.

[0149] (2) Preparation of negative electrode sheet

[0150] A 50 μm lithium foil was rolled onto an 8 μm copper foil to serve as a negative electrode sheet. The negative electrode sheet was then cut into a 41 mm × 51 mm rectangle for later use.

[0151] (3) Preparation of electrolyte

[0152] The electrolyte was prepared by uniformly mixing ethylene glycol dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and the primary lithium salt, lithium bis(fluorosulfonyl)imide (LiFSI). The molar ratio of LiFSI to DME was 1:1.1, and the molar ratio of LiFSI to TTE was 1:1.5.

[0153] (4) Preparation of isolation membrane

[0154] Polyethylene porous membrane is selected as the isolation membrane.

[0155] (5) Preparation of lithium metal battery monomers

[0156] A pre-cut positive electrode sheet with a pre-set lithium salt and two pre-cut negative electrode sheets were separated by a separator and wrapped in an aluminum-plastic film bag to form a laminated electrode assembly. 0.3g of the prepared electrolyte was injected, and the aluminum-plastic film bag was vacuum-pressed. After standing at room temperature (approximately 25°C) for at least 6 hours, capacity and cycling performance testing could begin.

[0157] The capacity of a lithium metal battery cell can be measured as follows: at 25°C, allow the cell to rest for 5 minutes, then discharge it at a constant current of 0.1C to 2.8V. After 5 minutes of rest, charge it at a constant current of 0.1C to 4.3V, then charge it at a constant voltage of 4.3V to a current of 0.05C. After 5 minutes of rest, discharge it at a constant current of 0.1C to 2.8V. The discharge capacity at this point is recorded as the capacity of the lithium metal battery cell. The capacity of a lithium metal battery cell is 140mAh.

[0158] The prepared lithium metal battery cells were subjected to charge and discharge cycle tests at an ambient temperature of 25°C (28 mA) at a rate of 0.2C, with charge and discharge cutoff voltages of 4.3V and 2.8V. When the discharge capacity after the cycle decayed to 80% of the initial discharge capacity, the lithium metal battery cell was considered to have reached the end of its life, and the number of cycles was recorded.

[0159] The prepared lithium metal battery cells were subjected to charge and discharge cycle tests at an ambient temperature of 60°C (28 mA) at a 0.2C rate, with charge and discharge cutoff voltages of 4.3V and 2.8V. When the discharge capacity after the cycle decayed to 80% of the initial discharge capacity, the lithium metal battery cell was considered to have reached the end of its life, and the number of cycles was recorded.

[0160] Examples 2 to 5

[0161] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 1, except that the mass ratios of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, and the first lithium salt are different. See Table 1 for details.

[0162] Comparative Example 1

[0163] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 1, except that the first lithium salt is not added when preparing the positive electrode plate.

[0164] Comparative Example 2

[0165] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 1, except that the preparation process of the positive electrode plate is different.

[0166] (1) Preparation of positive electrode sheet

[0167] First, LiNi 0.8 Co 0.1 Mn 0.1 O2 is used to coat lithium bis(fluorosulfonyl)imide (LiFSI). 0.8 Co 0.1 Mn 0.1 The mixture was mixed with O2 at a mass ratio of 100:1, subjected to high-energy ball milling at a stirring speed of 600 r / min for 2.5 h, and then sieved to obtain a coated positive electrode active material.

[0168] The coated positive electrode active material, positive electrode conductive agent acetylene black, and positive electrode binder polyvinylidene fluoride are mixed, and the solvent N-methylpyrrolidone is added and stirred evenly to obtain a positive electrode slurry with a solid content of about 65%. The positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature (about 25°C), and then transferred to an oven for further drying, and then cold pressed to obtain a positive electrode sheet. The positive electrode sheet is cut into a 40mm×50mm rectangle for use. The capacity of the single side of the positive electrode is 3.5mAh / cm 2 Up to 5mAh / cm 2 Between. 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, acetylene black and polyvinylidene fluoride is 100:1:1.

[0169] Table 1

[0170] It can be seen from the test results of Examples 1 to 5 and Comparative Example 1 that by adding a preset lithium salt to the positive electrode plate, the lithium metal battery cell using the positive electrode plate can have a better cycle life.

[0171] From the test results of Examples 1 to 5 and Comparative Example 2, it can be seen that by dispersing the first lithium salt in the positive electrode film layer, the cycle life of the lithium metal battery cell can be better improved. In Comparative Example 2, LiFSI is disposed on the surface of the positive electrode active material as a coating layer by high-energy ball milling. LiFSI will decompose and participate in the formation of the positive electrode protective film during the battery cell cycle, playing a role in stabilizing the interface of the positive electrode active material and improving the ionic conductivity of the positive electrode active material. However, LiFSI is difficult to fully dissolve in the electrolyte. Therefore, during the cycle of the lithium metal battery cell, the electrolyte concentration will continue to decrease, making it difficult to maintain the solvation structure of the initial high-concentration electrolyte, causing the electrolyte's redox resistance to continue to decrease, thereby resulting in an insufficiently excellent effect on improving the cycle life of the lithium metal battery cell.

[0172] It can also be seen from the test results of Examples 1 to 5 that the cycle life of the lithium metal battery cell can be better improved by further adjusting the mass content of the first lithium salt in the positive electrode film layer.

[0173] Examples 6 to 11

[0174] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 3, except that a second lithium salt is added to the positive electrode slurry. The type and content of the second lithium salt are detailed in Table 2.

[0175] Table 2

[0176] It can be seen from the test results of Example 3 and Examples 6 to 9 that the cycle life of the lithium metal battery cell can be better improved by further adding a second lithium salt to the positive electrode film layer.

[0177] From the test results of Examples 3 and 9 to 11, it can be seen that different mass proportions of the second lithium salt in the positive electrode film layer will lead to different degrees of improvement in the cycle life of the lithium metal battery cells.

[0178] Example 12

[0179] (1) Preparation of positive electrode sheet

[0180] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, positive electrode conductive agent acetylene black, positive electrode binder polyvinylidene fluoride, and the first lithium salt lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) are mixed in a mass ratio of 100:1:1:1, and the solvent N-methylpyrrolidone is added and stirred evenly to obtain a positive electrode slurry with a solid content of about 50%. The positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature (about 25°C), and then transferred to an oven for further drying, and then cold pressed to obtain a positive electrode sheet with a preset lithium salt. The positive electrode sheet is cut into a 40mm×50mm rectangle for standby use. The capacity of the single side of the positive electrode is 3.5mAh / cm 2 Up to 5mAh / cm 2 between.

[0181] (2) Preparation of negative electrode sheet

[0182] A 50 μm lithium foil was rolled onto an 8 μm copper foil to serve as a negative electrode sheet. The negative electrode sheet was then cut into a 41 mm × 51 mm rectangle for later use.

[0183] (3) Preparation of electrolyte

[0184] The electrolyte was prepared by uniformly mixing ethylene glycol dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and the primary lithium salt, lithium bis(fluorosulfonyl)imide (LiFSI). The molar ratio of LiFSI to DME was 1:1.1, and the molar ratio of LiFSI to TTE was 1:1.5.

[0185] (4) Preparation of isolation membrane

[0186] Polyethylene porous membrane is selected as the isolation membrane.

[0187] (5) Preparation of lithium metal battery monomers

[0188] A pre-cut positive electrode sheet with a pre-set lithium salt and two pre-cut negative electrode sheets were separated by a separator and wrapped in an aluminum-plastic film bag to form a laminated electrode assembly. 0.3g of the prepared electrolyte was injected, and the aluminum-plastic film bag was vacuum-pressed. After standing at room temperature (approximately 25°C) for at least 6 hours, capacity and cycling performance testing could begin.

[0189] Table 3

[0190] The test results of Examples 3 and 12 show that different types of the first lithium salt in the positive electrode film layer will have different degrees of improvement in the cycle life of the lithium metal battery cell. When the first lithium salt is LiFSI, the lithium metal battery cell can have a better cycle life.

[0191] Example 13 to Example 15

[0192] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 3, except that the composition of the electrolyte is different. The specific parameters are detailed in Table 4.

[0193] Table 4

[0194] It can be seen from the test results of Example 3 and Examples 13 to 15 that the cycle life of lithium metal battery cells can be increased by making the electrolyte have a high concentration.

[0195] Example 16 to Example 17

[0196] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 3, except that the composition of the electrolyte is different. The specific parameters are detailed in Table 5.

[0197] Table 5

[0198] From the test results of Example 3 and Examples 16 to 17, it can be seen that an appropriate amount of diluent can make the lithium metal battery monomer have a better cycle life.

[0199] Example 18 to Example 21

[0200] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 14, except that the composition of the electrolyte is different. Specific parameters are detailed in Table 6.

[0201] Table 6

[0202] From the test results of Example 14 and Examples 18 to 21, it can be seen that an appropriate amount of auxiliary lithium salt in the electrolyte can better improve the cycle life of lithium metal battery cells.

[0203] Example 22

[0204] The preparation method of the lithium metal battery cell and the test method of the cycle performance are the same as those in Example 3, except that the timing of adding the first lithium salt is different.

[0205] (1) Preparation of positive electrode sheet

[0206] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, acetylene black, a positive electrode conductive agent, and polyvinylidene fluoride, a positive electrode binder, are mixed in a mass ratio of 100:1:1, and N-methylpyrrolidone solvent is added and stirred evenly to obtain a positive electrode slurry with a solid content of 65%. The positive electrode slurry is then evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature (about 25°C), and transferred to an oven for further drying. Then, cold pressing is performed to obtain a positive electrode sheet with a preset lithium salt. A solution of ethylene glycol dimethyl ether containing the first lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) is applied to the surface of the positive electrode sheet, fully impregnated, and transferred to an oven for further drying to obtain a positive electrode sheet with a preset lithium salt. The solution of ethylene glycol dimethyl ether containing the first lithium salt lithium bis(fluorosulfonyl)imide (LiFSI) is 0.5 mol / L, and the mass ratio of the first lithium salt to the positive electrode active material is 5:100. Cut the positive electrode into a 40mm×50mm rectangle for later use. The capacity of the positive electrode on one side is 3.5mAh / cm 2 Up to 5mAh / cm 2 between.

[0207] Table 7

[0208] The test results of Examples 3 and 22 show that the timing of adding the first lithium salt slightly varies in improving the cycle life of lithium metal battery cells. Introducing the first lithium salt during the positive electrode slurry preparation process can make the first lithium salt more evenly distributed in the positive electrode film layer, thereby facilitating the uniform diffusion of the first lithium salt into the electrolyte, thereby improving the cycle performance of the lithium metal battery cells.

[0209] The various embodiments described above are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, wherein: A preset lithium salt is dispersed in the positive electrode film layer, and the preset lithium salt includes a first lithium salt having a structure shown in Formula 1, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, M1 is Li, 2. The positive electrode sheet according to claim 1, wherein: R1 and R2 each independently include a fluorine atom or a trifluoromethyl group.

3. The positive electrode sheet according to any one of claims 1 to 2, wherein: The mass percentage of the first lithium salt in the positive electrode film layer is 0.8 wt %-10 wt %.

4. The positive electrode sheet according to claim 3, wherein: The mass proportion of the first lithium salt in the positive electrode film layer is 2 wt %-6.5 wt %.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein: The preset lithium salt also includes a second lithium salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

6. The positive electrode sheet according to claim 5, wherein: The second lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium difluorophosphate.

7. The positive electrode sheet according to any one of claims 5 to 6, wherein: The molar ratio of the second lithium salt to the first lithium salt is 0.02:1-0.2:

1.

8. The positive electrode sheet according to claim 7, wherein: The molar ratio of the second lithium salt to the first lithium salt is 0.02:1-0.1:

1.

9. The positive electrode sheet according to any one of claims 1 to 8, wherein: The positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes one or more of lithium transition metal oxides, lithium-containing phosphates, and modified compounds thereof.

10. A battery cell, wherein: The positive electrode sheet comprises the positive electrode sheet according to any one of claims 1 to 9.

11. The battery cell according to claim 10, wherein: The battery cell includes an electrolyte, the electrolyte includes an electrolyte salt and a solvent, the electrolyte salt includes a main lithium salt, the main lithium salt includes a first lithium salt having a structure shown in Formula 1, R1 and R2 each independently include a fluorine atom or a C1-C6 fluoroalkyl group, M1 is Li, 12. The battery cell according to claim 11, wherein: The sum of the mass of the first lithium salt in the positive electrode film layer and the mass of the first lithium salt in the electrolyte is greater than the saturated solubility of the first lithium salt in the electrolyte.

13. The battery cell according to any one of claims 11 to 12, wherein: The solvent includes an ether compound.

14. The battery cell according to claim 13, wherein: The solvent includes one or more of methyl n-butyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,2-dimethoxypropane, 1,3-dimethoxypropane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

15. The battery cell according to any one of claims 11 to 14, wherein: The molar ratio of the main lithium salt to the solvent in the electrolyte is 1:0.8-1:

3.

16. The battery cell according to claim 15, wherein: The molar ratio of the main lithium salt to the solvent in the electrolyte is 1:1-1:

2.

17. The battery cell according to any one of claims 11 to 16, wherein: The electrolyte salt further includes an auxiliary lithium salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, and lithium tetrafluorooxalatophosphate.

18. The battery cell according to claim 17, wherein: The molar ratio of the auxiliary lithium salt to the main lithium salt in the electrolyte is 0.02:1-0.2:

1.

19. The battery cell according to claim 18, wherein: The molar ratio of the auxiliary lithium salt to the main lithium salt in the electrolyte is 0.05:1-0.1:

1.

20. The battery cell according to any one of claims 11 to 19, wherein: The electrolyte further includes a diluent, and the molar ratio of the main lithium salt to the diluent in the electrolyte is 1:0.5-1:

5.

21. The battery cell according to claim 20, wherein: The diluent includes one or more of fluoroether diluents, aromatic diluents, and fluorinated aromatic diluents.

22. The battery cell according to claim 21, wherein The diluent includes 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl, 1-(1,1,2,2-tetrafluoroethoxy)propane, 1,1,2,2-tetrafluoroethyl ethyl ether, bis(2,2,2-trifluoroethyl) ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, heptafluoropropyl 1,2,2,2-tetrafluoroethyl ether, 2,2,3 ,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ester, bis-(1,2,2,2-tetrafluoroethyl) ether, 1,1,2,3,3,3-pentafluoropropyl difluoromethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, benzene, 3-fluorobenzene, m-difluorobenzene, 1,3,5-trifluorobenzene, and one or more of anisole.

23. The battery cell according to any one of claims 10 to 22, wherein: The battery cell is a lithium metal battery cell or a negative electrode-free lithium metal battery cell.

24. A battery, wherein: A battery cell comprising the battery cell according to any one of claims 10 to 23.

25. An electrical device, wherein: The battery according to claim 24 is used to provide electrical energy.

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