Lithium metal battery cell, electrolyte, battery device, and electric device

Abstract

A lithium metal battery cell, an electrolyte, a battery device, and an electric device. The lithium metal battery cell comprises the electrolyte, and the electrolyte comprises a lithium salt, carbon quantum dots, an ether solvent, and a diluent, wherein the ether solvent is used for dispersing and / or dissociating the lithium salt, the diluent is used for diluting the ether solvent, and the lithium salt and the diluent are immiscible.

Description

Lithium metal battery cell, electrolyte, battery device and power utilization device

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202411369157.1, filed on September 29, 2024, entitled “Lithium metal battery cell, electrolyte, battery device and power utilization device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application belongs to the technical field of lithium metal battery cells, and specifically relates to a lithium metal battery cell, an electrolyte, a battery device and a power utilization device. BACKGROUND

[0004] With the rapid development of lithium batteries in the fields of electric vehicles, electric aviation, etc., the public's performance requirements for battery products are increasing due to the space limitations of application scenarios. Due to the high theoretical specific capacity (3860 mAh g-1) and low redox potential (-3.04 V vs. standard hydrogen electrode) of the lithium metal negative electrode, the energy density of the lithium metal battery cell can exceed 500 Wh / kg, which is one of the most potential next-generation battery systems. However, the negative electrode sheet in the lithium metal battery cell has a large volume change during charging and discharging, and the solid electrolyte interface film (SEI) at the interface between the negative electrode sheet and the electrolyte is repeatedly broken and regenerated during the cycle process, which affects the performance of the lithium metal battery cell.

[0005] Therefore, there is an urgent need to provide a lithium metal battery cell with good comprehensive performance. SUMMARY

[0006] The purpose of the present application is to provide a lithium metal battery cell that has improved cycle life and kinetic performance; the electrolyte of the present application can improve the cycle life and kinetic performance of the lithium metal battery cell. The battery device and the power utilization device comprising the lithium metal battery cell at least have the above-mentioned beneficial effects.

[0007] In a first aspect, the embodiments of the present application provide a lithium metal battery cell, the lithium metal battery cell comprising an electrolyte, the electrolyte comprising a lithium salt, carbon quantum dots, an ether solvent and a diluent, the ether solvent being used to disperse and / or dissociate the lithium salt; the diluent being used to dilute the ether solvent; the lithium salt and the diluent being immiscible.

[0008] In the embodiments of the present application, the electrolyte of the lithium metal battery cell comprises a lithium salt, an ether solvent and a diluent, the lithium salt and the diluent are not mutually soluble, and the ether solvent is used to disperse and / or dissociate the lithium salt; the diluent is used to dilute the ether solvent, forming an electrolyte with a local high concentration of lithium salt anions. The electrolyte has excellent compatibility with the negative electrode sheet of the lithium metal battery, and the lithium salt anions in the electrolyte can form a solid electrolyte layer (SEI) derived mainly from anions on the surface of the lithium metal, and promote uniform lithium deposition, thereby enhancing the stability of the solid electrolyte film, and improving the cycle life of the lithium metal battery cell compared with the conventional electrolyte.

[0009] In the embodiments of the present application, the electrolyte comprising a lithium salt, an ether solvent and a diluent will have a certain polarization phenomenon at the interface between the negative electrode sheet and the electrolyte after the lithium metal battery cell is subjected to electrochemical cycling, and the electrolyte film (SEI film) can be continuously damaged and reformed, thereby affecting the cycle capacity stability and kinetic performance of the lithium metal battery cell. The electrolyte of the present application contains carbon quantum dots, which are a zero-dimensional material and participate in the formation of the SEI film. The carbon quantum dots have abundant edge defects, and when the carbon quantum dots are in the SEI film, they can act as a fast diffusion channel for lithium ions, thereby improving the ionic conductivity of the SEI film, promoting the passage of lithium ions through the SEI film and uniform deposition on the negative electrode sheet, and improving the above-mentioned polarization phenomenon and the kinetic performance of the lithium metal battery cell.

[0010] In summary, in the later stage of the lithium metal battery cycle, the electrolyte with a local high concentration of lithium salt anions is more likely to cause damage to the SEI film and polarization at the interface between the negative electrode sheet and the electrolyte compared with the conventional electrolyte. The electrolyte system of the present application adds graphene quantum dots, and the components of the electrolyte synergistically provide the cycle life and kinetic performance of the lithium metal battery, which is reflected in the high rate and reversible capacity of the full life cycle.

[0011] In some optional embodiments, the mass concentration of the carbon quantum dots in the electrolyte is 0.01 mg / mL to 2 mg / mL. The content of the carbon quantum dots is uniformly attached to the ultra-thin lithium metal battery cell electrochemical interface (SEI film), thereby improving the cycle capacity retention rate and kinetic performance of the lithium metal battery cell.

[0012] In some optional embodiments, the mass concentration of the carbon quantum dots in the electrolyte is 0.1 mg / mL to 1 mg / mL. The mass concentration of the carbon quantum dots in the above range can participate in the formation of the SEI film, improve the ionic conductivity of the SEI film, promote the passage of lithium ions through the SEI film and uniform deposition on the negative electrode sheet, further improve the above-mentioned polarization phenomenon, and further improve the cycle capacity stability and kinetic performance of the lithium metal battery cell.

[0013] In some optional embodiments, the carbon quantum dots include one or more of graphene quantum dots, graphene oxide quantum dots, fluorinated graphene quantum dots, chlorinated graphene quantum dots, carboxylated graphene quantum dots, hydroxylated graphene quantum dots, and aminated graphene quantum dots.

[0014] In some optional embodiments, the lithium salt has a mass percentage content of 20% to 28% in the electrolyte.

[0015] The lithium salt has a mass content in the above range, which can reduce side reactions and the amount of lithium loss, reduce the formation of "dead lithium" in the battery, and thus improve the cycle capacity retention rate of the lithium metal battery cell; it can also optimize the interface properties of the electrode and the electrolyte, enhance the interface stability of the battery, and improve the service life of the lithium metal battery cell.

[0016] In some optional embodiments, the lithium salt includes one or more of lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis-trifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0017] In some optional embodiments, the mass ratio of the lithium salt, the ether solvent, and the diluent is 1:(0.4-3):(1-5). Controlling the mass of the lithium salt, the ether solvent, and the diluent in the above range can ensure that the impedance between the electrode and the electrolyte is low, which is conducive to the formation of a stable and dense SEI layer on the surface of the negative electrode tab, and improves the cycle capacity retention rate of the lithium metal battery cell. It can also promote the uniform deposition of lithium ions on the surface of the negative electrode, inhibit the generation of dendrites, and improve the reliability of the lithium metal battery cell.

[0018] In some optional embodiments, the mass ratio of the lithium salt, the ether solvent, and the diluent is 1:(1.2-2):(3-3.5). Therefore, the cycle capacity retention rate and the reliability of the lithium metal battery cell can be further improved.

[0019] In some optional embodiments, the ether solvent includes one or more of diethyl ether, dipropyl ether, ethyl propyl ether, methyl butyl ether, dibutyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol methyl ethyl ether, propylene glycol diethyl ether, butanediol dimethyl ether, butanediol methyl ethyl ether, butanediol diethyl ether, tetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, tetrahydropyran, 1,3-dioxane, and 1,4-dioxane.

[0020] In some optional embodiments, the diluent comprises one or more of benzene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluoromethylbenzene, trifluoromethoxybenzene, decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-dimethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(difluoromethoxy)ethane, 1,2-bis(trifluoromethoxy)ethane, 1,2-diethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, bis(2,2-difluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

[0021] In some optional embodiments, the electrolyte has a conductivity of 1 mS / cm to 10 mS / cm. The conductivity of the electrolyte reflects the migration ability of lithium ions in the electrolyte. The above-mentioned conductivity can reduce the internal resistance of the lithium metal battery cell, improve the charge transfer rate, and improve the kinetic performance, so that the lithium metal battery cell can maintain a high energy output at a high current density. The above-mentioned conductivity helps to reduce uneven current distribution and improve the cycle life of the lithium metal battery cell.

[0022] In some optional embodiments, the electrolyte has a conductivity of 2 mS / cm to 8 mS / cm. Thus, the cycle life and kinetic performance of the lithium metal battery cell are further improved.

[0023] In some optional embodiments, the electrolyte has a viscosity of 1 mPa s to 10 mPa s. The viscosity of the electrolyte affects the diffusion rate of lithium ions in the electrolyte. The viscosity of the electrolyte in the above-mentioned range helps to improve the diffusion coefficient of lithium ions, thereby accelerating the transfer speed of charges and improving the kinetic performance of the lithium metal battery cell. The electrolyte with the above-mentioned viscosity helps to balance the lithium deposition process, reduce dendrite formation, and improve the stability and cycle life of the lithium metal battery cell.

[0024] In some optional embodiments, the electrolyte has a viscosity of 1.5 mPa s to 8.5 mPa s. Thus, the cycle life and kinetic performance of the lithium metal battery cell are further improved.

[0025] In some optional embodiments, the lithium metal battery cell includes a negative electrode tab, the negative electrode tab includes a composite lithium layer, the composite lithium layer includes lithium metal and carbon quantum dots, the lithium metal is a continuous phase, and the carbon quantum dots are a dispersed phase.

[0026] In the embodiments of the present application, the composite lithium layer of the negative electrode tab contains lithium metal material and carbon quantum dots. The carbon quantum dots are a kind of zero-dimensional material, have rich edge defects and lithium affinity, and are uniformly dispersed in the lithium metal as uniform heterogeneous nucleation sites. The carbon quantum dots can also reduce the nucleation potential of lithium ions, facilitate the deposition and solvation of lithium ions, reduce the risk of lithium dendrite growth, and improve the reliability of the lithium metal battery. After the carbon quantum dots are uniformly dispersed in the lithium metal, they can be uniformly attached to the electrochemical interface (SEI film) of the ultra-thin lithium metal battery, guide the uniform and dense nucleation and deposition of lithium, reduce the anode / electrolyte interface polarization, and improve the cycle capacity retention rate of the lithium metal battery. During the electrochemical cycling of the lithium metal battery, as the lithium metal is consumed, the carbon quantum dots participate in the formation of the SEI film in situ, can act as a fast diffusion channel for lithium ions, and improve the ion conduction ability of the SEI film, which is beneficial to improving the kinetic performance of the lithium metal battery.

[0027] In addition, in the later stage of the electrochemical cycling of the lithium metal battery, the surface of the lithium metal negative electrode tab still contains uniform carbon quantum dots, which can achieve the regulation of the nucleation behavior of lithium metal throughout the life cycle of the lithium metal battery.

[0028] In some optional embodiments, the mass content of the carbon quantum dots in the composite lithium layer is 0.01% to 10%. Therefore, the carbon quantum dots can reduce the nucleation potential of lithium ions, facilitate the deposition and solvation of lithium ions, improve the reliability of the lithium metal battery, and improve the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0029] In some optional embodiments, the mass content of the carbon quantum dots in the composite lithium layer is 0.5% to 2%. Therefore, the cycle capacity retention rate and kinetic performance of the lithium metal battery are further improved.

[0030] In some optional embodiments, the carbon quantum dots include one or more of graphene quantum dots, graphene oxide quantum dots, fluorinated graphene quantum dots, chlorinated graphene quantum dots, carboxylated graphene quantum dots, hydroxylated graphene quantum dots, and aminated graphene quantum dots. The above-mentioned types of carbon quantum dots can improve the reliability of the lithium metal battery, improve the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0031] In some optional embodiments, the thickness of the composite lithium layer is 2-100 microns. The thickness of the composite lithium layer is in the above range, and the lithium metal battery includes uniformly distributed carbon quantum dots. During the charging and discharging process of the lithium metal battery, lithium can still be uniformly deposited due to repeated lithium deposition and stripping, thereby improving the cycle life and reliability of the lithium metal battery.

[0032] In some optional embodiments, the thickness of the composite lithium layer is 10-20 microns. Therefore, the cycle life and reliability of the lithium metal battery are further improved.

[0033] In some optional embodiments, the negative electrode tab includes a negative electrode current collector and a composite lithium layer arranged on at least one side of the negative electrode current collector. Therefore, such a negative electrode tab is beneficial to balancing the energy density and kinetic performance of the lithium metal battery.

[0034] In a second aspect, the embodiments of the present application provide an electrolyte for a lithium metal battery cell, which includes a lithium salt, carbon quantum dots, an ether solvent, and a diluent. The ether solvent is used to disperse and / or dissociate the lithium salt. The diluent is used to dilute the ether solvent. The lithium salt and the diluent are immiscible.

[0035] In the embodiments of the present application, the electrolyte of the lithium metal battery cell includes a lithium salt, an ether solvent, and a diluent. The lithium salt and the diluent are immiscible. The ether solvent is used to disperse and / or dissociate the lithium salt. The diluent is used to dilute the ether solvent, thereby forming an electrolyte with a locally high concentration of lithium salt anions. The electrolyte has excellent compatibility with the negative electrode tab of the lithium metal battery. The lithium salt anions in the electrolyte help to form a dense solid electrolyte film (SEI film), thereby enhancing the stability of the solid electrolyte film. Compared with a conventional electrolyte, the cycle life of the lithium metal battery cell is improved.

[0036] In the embodiments of the present application, the electrolyte containing the lithium salt, the ether solvent, and the diluent has a certain polarization phenomenon at the interface between the negative electrode tab and the electrolyte after the lithium metal battery cell is subjected to electrochemical cycling. The electrolyte film (SEI film) can be continuously damaged and reformed, thereby affecting the cycle capacity stability and kinetic performance of the lithium metal battery cell. The electrolyte of the embodiments of the present application contains carbon quantum dots. The carbon quantum is a zero-dimensional material and participates in the formation of the SEI film. The carbon quantum dots have rich edge defects. When the carbon quantum dots are in the SEI film, they can act as a fast diffusion channel for lithium ions, thereby improving the ionic conductivity of the SEI film, promoting the passage of lithium ions through the SEI film and the uniform deposition of lithium on the negative electrode tab, and improving the above-mentioned polarization phenomenon, thereby improving the kinetic performance of the lithium metal battery cell.

[0037] Compared with the traditional electrolyte, the electrolyte with a local high concentration of lithium salt anion is easy to cause damage to the SEI film and polarization of the negative electrode and electrolyte interface in the later stage of lithium metal battery cycle. Therefore, under the electrolyte system of the present application, the addition of graphene quantum dots, the synergistic effect of each component of the electrolyte, and the comprehensive provision of the cycle life and kinetic performance of the lithium metal battery, which is reflected in the high rate and reversible capacity of the whole life cycle.

[0038] In a third aspect, the embodiments of the present application provide a battery device comprising the lithium metal battery cell of the first aspect or the battery cell prepared by the electrolyte of the second aspect. The battery device of the present application comprises the lithium metal battery cell of the first aspect of the present application or the lithium metal battery cell prepared by the electrolyte of the second aspect, and thus at least has the advantages of the lithium metal battery cell or the electrolyte.

[0039] In a fourth aspect, the embodiments of the present application provide a power utilization device comprising the battery device of the third aspect. The power utilization device of the present application comprises the battery device of the third aspect of the present application, and thus at least has the corresponding advantages of the battery device. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by the drawings without creative labor for those skilled in the art.

[0041] FIG. 1 shows a schematic diagram of an embodiment of the lithium metal battery cell of the present application.

[0042] FIG. 2 shows an exploded schematic diagram of an embodiment of the lithium metal battery cell shown in FIG. 1.

[0043] FIG. 3 shows a schematic diagram of the overall battery pack of an embodiment of the present application.

[0044] FIG. 4 shows an exploded schematic diagram of the battery pack of an embodiment of the present application.

[0045] FIG. 5 shows a schematic diagram of an embodiment of a power utilization device comprising the lithium metal battery cell of the present application as a power source.

[0046] In the drawings, the drawings are not necessarily drawn to scale. The reference signs are explained as follows: 1, battery pack, 2, upper box body, 3, lower box body, 4, battery module, 5, lithium metal battery cell. DETAILED DESCRIPTION

[0047] Hereinafter, specific embodiments of the lithium metal battery cell, electrolyte, battery device, and power using device of the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known to those skilled in the art, repeated description of substantially identical configurations, is omitted. This is to avoid the following description becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0048] The ranges disclosed herein are defined by their lower and upper limits. Ranges that include both endpoints are inclusive of the endpoints. Ranges that exclude both endpoints are not inclusive of the endpoints. Ranges that include one or both endpoints are inclusive of the endpoint(s) and ranges that exclude one or both endpoints are not inclusive of the endpoint(s). Ranges are defined by their lower and upper limits. Unless specifically stated otherwise, the use of a range of values for a parameter includes each and every value and sub-range within the range. Exemplary values for physical parameters, such as temperature and pressure, are included in ranges unless otherwise stated herein. All ranges and parameters, including those for quantities, are inclusive of the recited endpoint and endpoints, unless expressly stated otherwise. For example, a range of "about 1% to 10%" is inclusive of from 1% to 10% but not including the endpoints 1% and 10%. All ranges and parameters are inclusive of the endpoints unless expressly stated otherwise. For example, a range of "about 1% to 10%" is inclusive of from 1% to 10% but not including the endpoints 1% and 10%.

[0049] Unless specifically stated otherwise, 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.

[0050] Unless specifically stated otherwise, all technical features and optional technical features 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.

[0051] If not otherwise specified, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, a method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, a method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] If not otherwise specified, the terms "first", "second", "third", "fourth" and the like in the present application are used to distinguish different objects, and are not used to describe a specific sequence or primary and secondary relationship.

[0053] If not otherwise specified, the term "active ion" in the present application refers to an ion that can be inserted and extracted between the positive and negative electrodes of a lithium metal battery cell, including but not limited to lithium ions and the like.

[0054] "Multiple" or "multiple" appearing in the present application refers to two or more (including two). "Several" or "several" appearing in the present application refers to two or more (including two).

[0055] The lithium metal battery cell mentioned in the embodiments of the present application can be a lithium ion lithium metal battery cell, a lithium metal battery cell, etc., and the embodiments of the present application are not limited thereto.

[0056] The battery device mentioned in the embodiments of the present application can include one or more lithium metal battery cells to provide a single physical module with higher voltage and capacity. For example, the battery device mentioned in the present application can include a lithium metal battery cell, a battery module, or a battery pack, etc.

[0057] In some optional embodiments, the battery device can be an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc. The battery device mentioned in the embodiments of the present application can include one or more lithium metal battery cell assemblies for providing voltage and capacity. The lithium metal battery cell assembly can include a plurality of lithium metal battery cells connected in series, parallel or mixed connection through a busbar component.

[0058] In some optional embodiments, the lithium metal battery cell assembly is usually formed by arranging a plurality of lithium metal battery cells; as an example, the lithium metal battery cell assembly can be a battery module formed by arranging and fixing a plurality of lithium metal battery cells into an independent module. As an example, the battery module can be formed by bundling a plurality of lithium metal battery cells with a cable tie.

[0059] In some alternative embodiments, the battery device can be a battery pack, which can include a case and one or more lithium metal battery cell assemblies housed in the case. In some alternative embodiments, the case can be part of a chassis structure of a vehicle. For example, part of the case can be at least part of a floor panel of the vehicle, or part of the case can be at least part of a cross beam and a longitudinal beam of the vehicle.

[0060] As an example, the lithium metal battery cell assembly can be a battery module, which can be housed in the case by fixing the battery module in the case.

[0061] As an example, the lithium metal battery cell assembly can also be housed in the case by fixing a plurality of lithium metal battery cells directly in the case.

[0062] A lithium metal battery cell is the smallest unit that constitutes a battery device, which is capable of charging and discharging by itself. The lithium metal battery cell can be in the shape of a cylinder, a cuboid, or other shapes, which are not limited in the embodiments of the present application. As an example, FIG. 1 is a lithium metal battery cell 5 in the shape of a cuboid.

[0063] When there are multiple lithium metal battery cells, the multiple lithium metal battery cells are connected in series, in parallel, or in a mixed connection through a current collection component. In some alternative embodiments, the battery can be a battery module; when there are multiple lithium metal battery cells, the multiple lithium metal battery cells are arranged and fixed to form a battery module.

[0064] In some alternative embodiments, the lithium metal battery cells can be assembled into a battery module, and the number of lithium metal battery cells contained in the battery module can be multiple, which can be adjusted according to the application and capacity of the battery module. FIG. 2 is a schematic diagram of a battery module 4 as an example. As shown in FIG. 2, in the battery module 4, multiple lithium metal battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the multiple lithium metal battery cells 5 can be fixed by fasteners.

[0065] Alternatively, the battery module 4 can further include a housing having an accommodation space, and the multiple lithium metal battery cells 5 are accommodated in the accommodation space.

[0066] In some alternative embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0067] FIGS. 3 and 4 are schematic diagrams of the battery pack 1 as an example. As shown in FIGS. 3 and 4, the battery pack 1 can include a case and a plurality of battery modules 4 disposed in the case. The case includes an upper case 2 and a lower case 3, the upper case 2 is used to cover the lower case 3, and forms a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the case in any manner.

[0068] The lithium metal battery cell provided by the embodiments of the present application can be a secondary battery, a primary battery, or the like. The lithium metal battery cell can be a secondary battery, which refers to a lithium metal battery cell that can be activated by charging after discharging to continue to be used.

[0069] The lithium metal battery cell provided by the embodiments of the present application includes an electrode assembly and an electrolyte, and the electrode assembly includes a positive electrode sheet and a negative electrode sheet. The negative electrode sheet can be a lithium metal negative electrode sheet. The electrode assembly can be a roll type structure or a stacked type structure, and the embodiments of the present application are not limited thereto. In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode sheet and the negative electrode sheet. In some embodiments, the separator is a separator film. The present application does not have special limitations on the type of separator film, and any known porous structure separator film with good chemical stability and mechanical stability can be selected. In some embodiments, the electrode assembly can not be provided with a separator, and the electrolyte can replace the separator to play a role.

[0070] The lithium metal battery cell can further include an outer package, which can be used to encapsulate the electrode assembly and the electrolyte. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package can also be a soft package, such as a bag type soft package. The material of the soft package can be plastic, such as one or more of aluminum plastic film, polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0071] It has been found through research that the solid electrolyte interface film (SEI) at the interface position of the negative electrode sheet and the electrolyte in the lithium metal battery cell is repeatedly broken and regenerated during electrochemical cycling, which triggers continuous reaction and consumption of active lithium and electrolyte, affecting the performance of the lithium metal battery cell. In addition, a large amount of electrolyte reaction products accumulate on the surface of the negative electrode sheet, causing serious polarization, which further leads to rapid deterioration of the cycle stability and rate performance of the battery. Therefore, the cycle life of the lithium metal battery cell using the conventional electrolyte is extremely short, which seriously hinders its practical application.

[0072] The reaction between the electrolyte and the negative electrode sheet is difficult to avoid, but the SEI film as a nanoscale passivation layer between lithium metal and electrolyte can alleviate the continuous reaction between lithium metal and electrolyte. At present, many new electrolyte systems have been developed to form a stable solid-state electrolyte interface film. However, the common problem faced by electrolyte is that due to the continuous reduction of anions at the later stage of cycling, the SEI components with low ionic conductivity are accumulated, the polarization of the negative electrode sheet is serious, and the cycle and rate performance of the battery cell drops sharply.

[0073] In view of this, the embodiments of the present application provide a lithium metal battery cell, which alleviates the continuous reaction between active lithium ions and electrolyte by designing electrolyte, and reduces the polarization of the negative electrode sheet to improve the cycle life and rate performance of the metal lithium battery at the later stage of cycling.

[0074] [Electrolyte]

[0075] The embodiments of the present application provide a lithium metal battery cell, which includes an electrolyte.

[0076] In some optional embodiments, the electrolyte includes a lithium salt, carbon quantum dots, an ether solvent, and a diluent, the ether solvent is used to disperse and / or dissociate the lithium salt; the diluent is used to dilute the ether solvent; and the lithium salt and the diluent are immiscible.

[0077] In the embodiments of the present application, the electrolyte of the lithium metal battery cell includes a lithium salt, an ether solvent, and a diluent, the lithium salt and the diluent are immiscible, the ether solvent is used to disperse and / or dissociate the lithium salt; and the diluent is used to dilute the ether solvent, forming an electrolyte with a local high concentration of lithium salt anions. The electrolyte has excellent compatibility with the negative electrode sheet of the lithium metal battery, and the lithium salt anions therein help to form a dense solid-state electrolyte film (SEI film), enhancing the stability of the solid-state electrolyte film and improving the cycle life of the lithium metal battery cell compared with the traditional electrolyte.

[0078] In the embodiments of the present application, the electrolyte containing a lithium salt, an ether solvent, and a diluent has a certain polarization phenomenon at the interface between the negative electrode sheet and the electrolyte at the later stage of electrochemical cycling of the lithium metal battery cell, and the electrolyte film (SEI film) may be continuously destroyed and reformed, affecting the cycle capacity stability and kinetic performance of the lithium metal battery cell. The electrolyte of the embodiments of the present application contains carbon quantum dots, which are zero-dimensional materials and participate in the formation of the SEI film. The carbon quantum dots have abundant edge defects, and when the carbon quantum dots are in the SEI film, they can act as a fast diffusion channel for lithium ions, improve the ionic conductivity of the SEI film, promote the lithium ions to pass through the SEI film and deposit uniformly on the negative electrode sheet, improve the above-mentioned polarization phenomenon, and improve the kinetic performance of the lithium metal battery cell.

[0079] In summary, compared with the traditional electrolyte, the electrolyte with a local high concentration of lithium salt anions is easy to cause damage to the SEI film and polarization at the interface between the negative electrode and the electrolyte during the later stage of electrochemical cycling of the lithium metal battery cell. Therefore, the addition of graphene quantum dots to the electrolyte system of the present application provides the cycle life and kinetic performance of the lithium metal battery in combination with the components of the electrolyte, which is reflected in the high rate and reversible capacity throughout the life cycle.

[0080] In some optional embodiments, the mass concentration of carbon quantum dots in the electrolyte is 0.01 mg / mL to 2 mg / mL. The content of carbon quantum dots is uniformly attached to the ultra-thin lithium metal battery cell electrochemical interface (SEI film), which improves the cycle capacity retention rate and kinetic performance of the lithium metal battery cell.

[0081] Alternatively, the mass concentration of carbon quantum dots in the electrolyte can be any value or range consisting of 0.01 mg / mL, 0.02 mg / mL, 0.03 mg / mL, 0.04 mg / mL, 0.05 mg / mL, 0.06 mg / mL, 0.07 mg / mL, 0.08 mg / mL, 0.09 mg / mL, 0.10 mg / mL, 0.2 mg / mL, 0.3 mg / mL, 0.4 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.7 mg / mL, 0.8 mg / mL, 0.9 mg / mL, 1.0 mg / mL.

[0082] In some optional embodiments, the mass concentration of carbon quantum dots in the electrolyte is 0.1 mg / mL to 1 mg / mL. The mass concentration of carbon quantum dots in the above range can participate in the formation of the SEI film, improve the ionic conductivity of the SEI film, promote the deposition of lithium ions through the SEI film and on the negative electrode, and further improve the above polarization phenomenon, thereby further improving the cycle capacity stability and kinetic performance of the lithium metal battery cell.

[0083] In some optional embodiments, the carbon quantum dots include one or more of graphene quantum dots, graphene oxide quantum dots, fluorinated graphene quantum dots, chlorinated graphene quantum dots, carboxylated graphene quantum dots, hydroxylated graphene quantum dots, and aminated graphene quantum dots.

[0084] Exemplarily, the carboxylated graphene quantum dots have strong electronegativity due to the carboxyl group, which makes them have high lithium ion affinity, which is beneficial to improve the lithium ion conductivity and improve the kinetic performance of the lithium metal battery cell.

[0085] In some optional embodiments, the carbon quantum dots include a polar group or a polar atom. The polar group includes one or more of a carboxyl group, an amino group, and a hydroxyl group. The polar atom includes one or more of an oxygen atom and a chlorine atom. The carbon quantum dots are rich in polar groups, which can be uniformly dispersed in the electrolyte. For example, the carbon quantum dots can be uniformly dispersed by means such as ultrasonic, stirring, and the like.

[0086] In some optional embodiments, the mass percentage content of the lithium salt in the electrolyte is 20% to 28%.

[0087] Alternatively, the mass percentage content of the lithium salt in the electrolyte can be any value or a range composed of any value selected from 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, and 28%. In some optional embodiments, the mass percentage content of the lithium salt in the electrolyte is 24% to 25%.

[0088] The mass content of the lithium salt in the above range can reduce unnecessary side reactions or loss of active lithium ions, reduce the formation of “dead lithium” in the battery, and thus improve the cycle capacity retention rate of the lithium metal battery cell; and can also optimize the interface properties of the electrode and the electrolyte, enhance the interface stability of the battery, and improve the service life of the lithium metal battery cell.

[0089] In some optional embodiments, the lithium salt includes one or more of lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bisoxalate borate, lithium difluorobisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate. The mass content of the lithium salt in the above range can provide sufficient lithium ions to improve the ionic conductivity of the electrolyte, thereby improving the kinetic performance of the lithium metal battery cell; the lithium salt can help form a stable solid electrolyte interface layer (SEI layer) on the surface of the electrode, protect the electrode material, reduce side reactions, and improve the cycle life of the lithium metal battery cell. The lithium salt can improve the thermal stability of the electrolyte and improve the reliability of the lithium metal battery cell.

[0090] In some optional embodiments, the mass ratio of the lithium salt, the ether-based solvent, and the diluent is 1:(0.4-3):(1-5).

[0091] Optionally, the ratio of the amount of substance of the lithium salt, the ether solvent and the diluent is any ratio in 1:0.4:1, 1:0.5:1, 1:0.6:1, 1:0.7:1, 1:0.8:1, 1:0.9:1, 1:1:1, 1:1.1:1, 1:1.2:1, 1:1.3:1, 1:1.4:1, 1:1.5:1, 1:1.6:1, 1:1.7:1, 1:1.8:1, 1:1.9:1, 1:2:1, 1:2.1:1, 1:2.2:1, 1:2.3:1, 1:2.4:1, 1:2.5:1, 1:2.6:1, 1:2.7:1, 1:2.8:1, 1:2.9:1, 1:3:1, 1:0.4:2, 1:0.5:3, 1:0.6:4, 1:0.7:5, 1:2:2, 1:3:3, 1:3:4, 1:3:5 or a range composed of the above. The amount of substance of the lithium salt, the ether solvent and the diluent is in the above range, which can ensure that the impedance between the electrode and the electrolyte is low, which is conducive to the formation of a stable and dense SEI layer on the surface of the negative electrode sheet, and improves the cycle capacity retention rate of the lithium metal battery cell. It can also promote the uniform deposition of lithium ions on the surface of the negative electrode, inhibit the generation of dendrites, and improve the reliability of the lithium metal battery cell.

[0092] In some optional embodiments, the ratio of the amount of substance of the lithium salt, the ether solvent and the diluent is 1:(1.2-2):(3-3.5). Therefore, the cycle capacity retention rate and the reliability of the lithium metal battery cell can be further improved.

[0093] In some optional embodiments, the ether solvent includes one or more of diethyl ether, dipropyl ether, ethyl propyl ether, methyl butyl ether, dibutyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol methyl ethyl ether, propylene glycol diethyl ether, butanediol dimethyl ether, butanediol methyl ethyl ether, butanediol diethyl ether, tetrahydrofuran, 3-methyl tetrahydrofuran, 1,3-dioxolane, tetrahydropyran, 1,3-dioxane and 1,4-dioxane.

[0094] In some optional embodiments, the diluent includes one or more of benzene (BZ), fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluoromethylbenzene, trifluoromethoxybenzene, decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-dimethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(difluoromethoxy)ethane, 1,2-bis(trifluoromethoxy)ethane, 1,2-diethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, bis(2,2-difluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

[0095] In some optional embodiments, the electrolyte solution further optionally includes an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving certain properties of the lithium metal battery cell, such as an additive capable of improving overcharge / fast charge properties of the lithium metal battery cell, an additive capable of improving high temperature properties of the lithium metal battery cell, an additive capable of improving low temperature properties of the lithium metal battery cell, and the like.

[0096] Methods for preparing electrolyte solutions are known. For example, the electrolyte salt (lithium salt), solvent, and optional additive can be mixed uniformly to obtain the electrolyte solution. The order of adding the materials during the preparation process is not particularly limited, and the materials can be added simultaneously or in batches.

[0097] The components in the electrolyte solution and their contents can be determined according to conventional methods in the art. For example, gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy, Raman spectroscopy, nuclear magnetic resonance, and the like can be used for detection.

[0098] As an example, the infrared spectroscopy method can be used to determine the compounds contained in the electrolyte solution. For example, the characteristic peak of the sulfur-oxygen double bond in the sulfoxide compound is at 1060 cm -1 -1040 cm -1The different components in the electrolyte can be separated and high-precision molecular weights can be obtained by high-resolution gas chromatography-high-resolution mass spectrometry, so that the atomic composition can be determined; then the specific molecular structure of each component is confirmed by the spectrum results of nuclear magnetic resonance.

[0099] As an example, the content of electrolyte salt in the electrolyte can be tested by ion chromatography (IC), and the content of each component in the organic solvent can be tested by gas chromatography-mass spectrometry (GC-MS).

[0100] The electrolyte can be sampled and analyzed during preparation, or the prepared lithium metal battery monomer can be discharged, disassembled, and centrifuged.

[0101] In some optional embodiments, the conductivity of the electrolyte is 1 mS / cm to 10 mS / cm.

[0102] Alternatively, the conductivity of the electrolyte can be any value in 1.0 mS / cm, 1.5 mS / cm, 2.0 mS / cm, 2.5 mS / cm, 3.0 mS / cm, 3.5 mS / cm, 4.0 mS / cm, 4.5 mS / cm, 5.0 mS / cm, 5.5 mS / cm, 6.0 mS / cm, 6.5 mS / cm, 7.0 mS / cm, 7.5 mS / cm, 8.0 mS / cm, 8.5 mS / cm, 9.0 mS / cm, 9.5 mS / cm, 10.0 mS / cm or a range composed thereof. In some optional embodiments, the conductivity of the electrolyte is 2 mS / cm to 8 mS / cm.

[0103] The conductivity of the electrolyte reflects the migration ability of lithium ions in the electrolyte. The above-mentioned conductivity can reduce the internal resistance of the lithium metal battery monomer, improve the charge transfer rate, improve the kinetic performance, and enable the lithium metal battery monomer to maintain a high energy output under high current density. The above-mentioned conductivity helps to reduce uneven current distribution and improve the cycle life of the lithium metal battery monomer.

[0104] The conductivity of the electrolyte can be obtained by testing with a conductivity meter. Illustratively, an appropriate amount of electrolyte can be taken and divided into 3 parts, and then the conductivity of each sample is determined at 25°C using a conductivity meter, and the average value of the test results is taken as the conductivity of the electrolyte. The testing instrument can be a DDS-307 conductivity meter.

[0105] In some optional embodiments, the viscosity of the electrolyte is 1 mPa·s to 10 mPa·s.

[0106] Optionally, the electrolyte can have a viscosity of any value in the range consisting of 1.0 mPa s, 1.5 mPa s, 2.0 mPa s, 2.5 mPa s, 3.0 mPa s, 3.5 mPa s, 4.0 mPa s, 4.5 mPa s, 5.0 mPa s, 5.5 mPa s, 6.0 mPa s, 6.5 mPa s, 7.0 mPa s, 7.5 mPa s, 8.0 mPa s, 8.5 mPa s, 9.0 mPa s, 9.5 mPa s, 10.0 mPa s, or a range composed thereof. In some optional embodiments, the electrolyte has a viscosity of 1.5 mPa s to 8.5 mPa s.

[0107] The viscosity of the electrolyte affects the diffusion rate of lithium ions in the electrolyte. The viscosity of the electrolyte in the above range helps to improve the diffusion coefficient of lithium ions, thereby accelerating the transfer speed of electric charges and improving the kinetic performance of the lithium metal battery cell. The electrolyte with the above viscosity helps to balance the lithium deposition process, reduces dendrite formation, and improves the stability and cycle life of the lithium metal battery cell.

[0108] The viscosity of the electrolyte can be tested using a viscometer. The shear force experienced by the rotor when rotating at a constant speed in the sample continuously causes the spring to generate a torque, and the torque is proportional to the viscosity, thereby obtaining the viscosity value of the sample.

[0109] As an example, the viscosity of the electrolyte can be tested as follows: under the condition of ambient humidity < 80%, take 30 mL of sample and place it in a water bath at 25°C for at least 30 min, install the rotor (e.g., No. 18 rotor) into the sample cup, add the sample to about 0.3 cm from the cup mouth, start the connected viscometer, select a rotation speed of 70 RPM for 5 min, and then read the viscosity value. Ten data points can be collected during testing, and the average value is taken. The testing instrument can be a Brookfield DV-2TLV viscometer.

[0110] [anode sheet]

[0111] In some optional embodiments, the lithium metal battery cell comprises an anode sheet, the anode sheet comprises a composite lithium layer, the composite lithium layer comprises lithium metal and carbon quantum dots, the lithium metal is a continuous phase, and the carbon quantum dots are a dispersed phase.

[0112] In the embodiments of the present application, the composite lithium layer of the negative pole piece contains lithium metal material and carbon quantum dots. The carbon quantum dots are a zero-dimensional material, have rich edge defects and lithium affinity, and are uniformly dispersed in the lithium metal as uniform heterogeneous nucleation sites. The carbon quantum dots can also reduce the nucleation potential of lithium ions, facilitate the deposition and solvation of lithium ions, reduce the risk of lithium dendrite growth, and improve the reliability of the lithium metal battery. After the carbon quantum dots are uniformly dispersed in the lithium metal, they can be uniformly attached to the electrochemical interface (SEI film) of the ultra-thin lithium metal battery, guide the uniform and dense nucleation and deposition of lithium, reduce the anode / electrolyte interface polarization, and improve the cycle capacity retention rate of the lithium metal battery. During the electrochemical cycling of the lithium metal battery, as the lithium metal is consumed, the carbon quantum dots participate in the formation of the SEI film in situ, can act as a fast diffusion channel for lithium ions, and improve the ion conduction ability of the SEI film, which is beneficial to improving the kinetic performance of the lithium metal battery.

[0113] In addition, in the later stage of the electrochemical cycling of the lithium metal battery, the surface of the lithium metal negative pole piece still contains uniform carbon quantum dots, which can achieve the regulation of the nucleation behavior of lithium metal throughout the life cycle of the lithium metal battery.

[0114] In some optional embodiments, the mass content of the carbon quantum dots in the composite lithium layer is 0.01% to 10%. Therefore, the carbon quantum dots can reduce the nucleation potential of lithium ions, facilitate the deposition and solvation of lithium ions, improve the reliability of the lithium metal battery, and uniformly attach the carbon quantum dots to the electrochemical interface (SEI film) of the ultra-thin lithium metal battery, thereby improving the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0115] The mass content of the carbon quantum dots in the composite lithium layer can be observed by scanning electron microscopy to observe the distribution of the carbon quantum dots in the metal layer, and energy dispersive X-ray spectroscopy (EDS) can be used to measure the mass of the particles.

[0116] Alternatively, any value or range consisting of any of 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, or a combination thereof.

[0117] In some optional embodiments, the mass content of the carbon quantum dots in the composite lithium layer is 0.5% to 2%. Therefore, the cycle capacity retention rate and kinetic performance of the lithium metal battery are further improved.

[0118] In some optional embodiments, the carbon quantum dots include one or more of graphene quantum dots, graphene oxide quantum dots, fluorinated graphene quantum dots, chlorinated graphene quantum dots, carboxylated graphene quantum dots, hydroxylated graphene quantum dots, and aminated graphene quantum dots. The above-mentioned types of carbon quantum dots can improve the reliability of the lithium metal battery, and improve the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0119] In some optional embodiments, the thickness of the composite lithium layer is 2-100 microns.

[0120] Optionally, any value or range consisting of 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm.

[0121] The thickness of the composite lithium layer is in the above range, and the carbon quantum dots are uniformly distributed therein. During the charging and discharging process of the lithium metal battery, lithium can still be uniformly deposited due to repeated lithium deposition and stripping, thereby improving the cycle life and reliability of the lithium metal battery.

[0122] An exemplary test method for the thickness of the composite lithium layer is as follows: a sample with a length of 50 mm and a width of 10 mm is taken; 5 points are uniformly taken on the sample (for example, one point is taken every 5 mm along the length direction of the sample), and the thickness of the composite lithium layer at the 5 different positions is tested by using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and the average value is taken as the thickness of the composite lithium layer.

[0123] In some optional embodiments, the thickness of the composite lithium layer is 10-20 microns. Therefore, the cycle life and reliability of the lithium metal battery are further improved.

[0124] In some optional embodiments, the thickness of the negative electrode tab can be 2-200 microns, optionally 6-120 microns, and optionally 140 microns.

[0125] In some optional embodiments, the negative electrode tab includes a negative electrode current collector and a composite lithium layer arranged on at least one side of the negative electrode current collector. Therefore, such a negative electrode tab is conducive to balancing the energy density and kinetic performance of the lithium metal battery.

[0126] In some optional embodiments, the thickness of the negative electrode current collector can be 0-20 microns, and optionally 4-12 microns.

[0127] The negative current collector can be a metal material, including but not limited to one or more of copper, nickel, lithium, iron, or stainless steel. It can be understood that any material of the negative current collector can support the function of the composite lithium foil. In some alternative embodiments, the negative electrode sheet is a composite lithium layer, which can not include a negative current collector.

[0128] In some alternative embodiments, the negative current collector includes one or more of lithium monomer, lithium alloy.

[0129] In some alternative embodiments, the negative current collector can include a metal foil, a three-dimensional porous current collector, or a composite current collector. As an example of the metal foil, copper foil, copper alloy foil, nickel foil, nickel alloy foil, aluminum foil, and aluminum alloy foil can be used. As an example of the three-dimensional porous current collector, copper mesh, nickel mesh, aluminum mesh, foamed copper, foamed nickel, and foamed aluminum can be used. The composite current collector can 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 can include but is not limited to one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include but is not limited to one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0130] Embodiments of the present application provide a preparation method of a negative electrode sheet for a lithium metal battery, including:

[0131] heating the lithium metal and the carbon quantum dots in an inert atmosphere to form a flow phase of the lithium metal;

[0132] dispersing the carbon quantum dots in the lithium metal of the flow phase to obtain a uniformly dispersed mixture;

[0133] cold-pressing the mixture to obtain a composite lithium layer.

[0134] In the present embodiment, the melting point of lithium metal is generally 180.5°C, and the melting point of carbon quantum dots is generally much higher than that of lithium metal. By dispersing the carbon quantum dots in the lithium metal of the flow phase, the carbon quantum dots can be uniformly dispersed in the lithium metal to form a composite lithium layer. The preparation method of the present application is simple, easy to operate, has good repeatability, is low in cost, and is environmentally friendly, and is suitable for industrial production.

[0135] The carbon quantum dots uniformly dispersed in the lithium metal can also reduce the nucleation potential of lithium ions, which is beneficial to the deposition and solvation of lithium ions, and can reduce the risk of lithium dendrite growth, thereby improving the reliability of the lithium metal battery. After the carbon quantum dots are uniformly attached to the ultra-thin lithium metal battery electrochemical interface (SEI film), the carbon quantum dots can guide the uniform and dense nucleation and deposition of lithium, reduce the anode / electrolyte interface polarization, and improve the cycle capacity retention rate of the lithium metal battery. During the electrochemical cycle of the lithium metal battery, as the lithium metal is consumed, the carbon quantum dots participate in the formation of the SEI film in situ, can act as a rapid diffusion channel for lithium ions, and can improve the ion conduction ability of the SEI film, thereby improving the kinetic performance of the lithium metal battery.

[0136] In some optional embodiments, the inert atmosphere can include inert gases such as nitrogen, argon, etc.

[0137] In some optional embodiments, the target temperature of heating can be 180.5-220°C. The carbon quantum dots can be dispersed in the lithium metal in the mobile phase by stirring or the like. The stirring time can be 0.5-1.5 hours.

[0138] In some optional embodiments, before the cold-pressed mixture is obtained, the method comprises:

[0139] Cooling the mixture.

[0140] In some optional embodiments, before the cold-pressed mixture is obtained, the method comprises:

[0141] The mixture is cold-pressed on a precision roller press to obtain the composite lithium layer. The gap of the precision roller press can be 2-100 microns.

[0142] In some optional embodiments, the method for preparing the negative electrode sheet further comprises:

[0143] The composite lithium layer is cold-pressed with the negative electrode current collector to obtain the negative electrode sheet.

[0144] [Positive electrode sheet]

[0145] In some optional embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer comprises a positive electrode active material. For example, the positive electrode current collector has two opposite surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0146] The type of the positive electrode active material can be selected according to the type of the lithium metal battery cell, and the embodiments of the present application are not limited in this regard.

[0147] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material is provided on either one or both of the two surfaces of the positive electrode current collector.

[0148] As an example, the positive electrode current collector can employ a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as the metal foil, a pure metal, an alloy, a surface-treated metal, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium, or silver, and the like can be employed. The composite current collector can include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and the like) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, and the like).

[0149] As an example, the positive electrode active material can include at least one of a lithium-containing phosphate, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material can also be used. These positive electrode active materials can be used alone only one or two or more can be used in combination. Among them, examples of the lithium-containing phosphate can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0150] Examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn0.1 O2(also can be referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.8 Co 0.15 Al 0.05 O2), and modified compounds thereof. The modified compounds refer to substances obtained by modification means such as doping or coating on the basis of the above-mentioned substances.

[0151] The battery cell will be accompanied by Li de-intercalation and consumption during charging and discharging, and the molar content of Li is different when the battery cell is discharged to different states. In the enumeration of the positive electrode active material in the present disclosure, the molar content of Li is the initial state of the material, i.e. the state before feeding, and the positive electrode active material is applied to the battery cell. After charging and discharging cycle, the molar content of Li will change. In the enumeration of the positive electrode active material in the present disclosure, the molar content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of O to change, and the actual molar content of O will also appear to float.

[0152] In some optional embodiments, the positive electrode can adopt a foam metal. The foam metal can be foam nickel, foam copper, foam aluminum, foam alloy, or foam carbon, etc. When the foam metal is used as the positive electrode, the surface of the foam metal can not be provided with the positive electrode active material, of course, the positive electrode active material can also be provided. As an example, the positive electrode active material is filled or / and deposited in the foam metal.

[0153] In some optional embodiments, the positive electrode film layer also optionally includes a positive electrode conductive agent. As an example, the positive electrode conductive agent can include but is not limited to one or more of super-conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0154] In some optional embodiments, the positive electrode film layer also optionally includes a positive electrode binder. As an example, the positive electrode binder can include but is not limited to one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester-based resin.

[0155] In some alternative embodiments, the positive current collector can employ a metal foil or a composite current collector. As an example of a metal foil, an aluminum foil can be employed. The composite current collector can 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 can include, but is not limited to, one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer can include, but is not limited to, one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0156] The positive electrode film layer can be formed by coating a positive electrode slurry on a positive current collector, drying, and cold-pressing. The positive electrode slurry is generally formed by dispersing and uniformly stirring a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0157] [Separator]

[0158] In some embodiments, the electrode assembly further includes a separator disposed between the positive electrode tab and the negative electrode tab.

[0159] In some embodiments, the separator can be a separator film. The type of the separator film is not particularly limited in the present application, and any publicly known porous structure separator film having good chemical stability and mechanical stability can be used.

[0160] As an example, the main material of the separator film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, and ceramic. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited. The separator can be a separate member located between the positive and negative electrodes, or can be attached to the surface of the positive and negative electrodes. An inorganic particle coating layer, an organic particle coating layer, or an organic / inorganic composite coating layer can be applied to the surface of the separator film.

[0161] In some embodiments, the separator is a solid electrolyte. The solid electrolyte is disposed between the positive and negative electrodes, and functions to transport ions and separate the positive and negative electrodes.

[0162] The preparation method of the lithium metal battery cell is known. In some optional embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form the lithium metal battery cell. As an example, the positive electrode sheet, the separator, the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in an outer package, the electrolyte is injected after drying, and the lithium metal battery cell is obtained after processes such as vacuum packaging, standing, formation, shaping, etc. A plurality of lithium metal battery cells can further be connected in series or in parallel or in a hybrid manner to form a lithium metal battery cell module. A plurality of lithium metal battery cell modules can be connected in series or in parallel or in a hybrid manner to form a lithium metal battery cell pack. In some optional embodiments, a plurality of lithium metal battery cells can be directly connected to form a lithium metal battery cell pack.

[0163] Electric device

[0164] The embodiments of the present application provide an electric device including the battery device described above.

[0165] The lithium metal battery cell can be used as a power source of the electric device, or as an energy storage unit of the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a notebook 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 and a satellite, an energy storage system, etc.

[0166] The electric device can select the lithium metal battery cell, the lithium metal battery cell module or the lithium metal battery cell pack according to its use requirements.

[0167] FIG. 5 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high power and high energy density of the electric device, the lithium metal battery cell pack or the lithium metal battery cell module can be used.

[0168] The electric device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The electric device usually requires thin and light, and the lithium metal battery cell can be used as a power source.

[0169] Embodiments

[0170] The present application is described in more detail by the following examples, which are merely illustrative and not limiting the scope of the present application, since various modifications and changes in the examples disclosed herein will occur to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported herein are based upon the weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used without further purification, and the instruments used in the examples are commercially available.

[0171] Example 1

[0172] Preparation of electrolyte:

[0173] Preparation of electrolyte mother liquor: Take lithium salt LiFSI, dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and mix them uniformly in a molar ratio of 1:1.2:3 to form a locally high-concentration mother liquor 1, i.e. a mixture without carbon quantum dots. Then take 0.001 g of carboxylated graphene quantum dots and mix them with the mother liquor 1 to prepare 10 g of electrolyte. After the electrolyte is fully stirred and mixed uniformly, a light black transparent state is formed.

[0174] Preparation of lithium metal battery:

[0175] Preparation of positive electrode sheet: mix the positive electrode active material lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), conductive agent acetylene black, and polyvinylidene fluoride PVDF in a mass ratio of 98:1:1, add solvent N-methyl pyrrolidone (NMP) and stir until the system is uniform to obtain a positive electrode slurry. The solid content of the positive electrode slurry is 70%; coat the positive electrode slurry on both sides of the positive electrode current collector aluminum foil with a loading of 12.5 mg / cm 2 , and transfer it to an oven for further drying after drying at room temperature, and then cut it into a 40 mm*50 mm rectangle as a positive electrode sheet.

[0176] Separator film: select a polyethylene porous film with a thickness of 12 microns and cut it into a 45 mm*55 mm rectangle for standby use.

[0177] Preparation of negative electrode sheet: coat a 50 μm lithium foil on a 12 μm copper foil by rolling, and then cut it into a 41 mm*51 mm rectangle as a negative electrode sheet.

[0178] Assembly: take a piece of cut positive electrode and two pieces of cut negative electrode to match, use the above-mentioned separator to isolate the positive and negative electrodes in the middle, and wrap it in an aluminum plastic film bag to form a stacked dry battery. Inject 0.3g of the above prepared electrolyte, vacuum heat seal the aluminum plastic film bag, and stand at room temperature for at least 6 hours before starting the cycle test. The rated capacity of the stacked battery prepared in this way is 70mAh.

[0179] Examples 2 to 5

[0180] Examples 2-5 are consistent with Example 1, except that the mass content of carbon quantum dots in the electrolyte is different, as shown in Table 2.

[0181] Examples 6-10

[0182] Examples 6-10 are consistent with Example 1, except that the types of carbon quantum dots in the electrolyte are different, as shown in Table 2.

[0183] Examples 11-18

[0184] Prepare different electrolyte mother liquor, mix the corresponding mother liquor with carbon quantum dots, and fully stir to form a light black transparent state, as shown in Table 1.

[0185] Table 1

[0186] Examples 11 to 18 are different from Example 1 in that the mother liquor for preparing the electrolyte is different. The test results are shown in Table 2.

[0187] Example 19

[0188] Example 19 is different from Example 1 in that the negative electrode sheet is different, and the composition of the negative electrode sheet is different. Preparation of the negative electrode sheet: a. Place lithium metal and carboxylated graphene quantum dots in a mass ratio of 99.5:0.5 in an argon-protected reactor and heat to 185°C, and stir uniformly at constant temperature;

[0189] b. Cool the above-mentioned stirred composite lithium metal;

[0190] c. The above-mentioned cooled composite lithium metal is cold-pressed into a 50-micron composite lithium foil on a precision rolling machine;

[0191] d. Roll the composite lithium foil and 12-micron copper foil to form a negative electrode sheet, and cut into a 41mm*51mm rectangle as a negative electrode sheet for standby. The test results are shown in Table 3.

[0192] Example 20

[0193] Example 20 differs from Example 1 in that the negative electrode sheet is prepared differently, and the mass content of carboxylated graphene quantum dots in the composite lithium foil is 1%. The test results are shown in Table 3.

[0194] Comparative Example 1

[0195] This comparative example is consistent with Example 1, except that only mother liquor 1 is used for lithium metal battery liquid injection and subsequent testing, without adding graphene quantum dots.

[0196] Test Part

[0197] 1) Lithium metal battery cycle performance test

[0198] Take the above prepared stack cells, set the ambient temperature to 25°C, use 0.2C (i.e. 14mA) charging, 1C discharging (i.e. 70mA) rate for charge-discharge cycle. The cut-off voltage of charge and discharge is set to 4.3V and 2.8V respectively, and the charging process adopts constant current-constant voltage charging method, specifically, after 0.2C constant current charging reaches the cut-off voltage 4.3V, continue to use 4.3V constant voltage charging until the current decays to 0.1C (i.e. 7mA). When the cycle number of the discharge capacity decay to 80% of the first circle discharge capacity, the cycle life of lithium metal battery is considered.

[0199] 2) Initial rate test of lithium metal battery

[0200] Take the above prepared stack cells, set the ambient temperature to 25°C, use 0.2C (i.e. 14mA) charging rate, use 0.2C (i.e. 14mA), 0.5C (i.e. 35mA), 1C (i.e. 70mA), 2C (i.e. 140mA), 4C (i.e. 280mA) discharging rate for charge-discharge once. The cut-off voltage of charge and discharge is set to 4.3V and 2.8V respectively, and the charging process adopts constant current-constant voltage charging method, and the capacity under 4C discharging rate is taken as the initial discharge capacity. Specifically, after 0.2C constant current charging reaches the cut-off voltage 4.3V, continue to use 4.3V constant voltage charging until the current decays to 0.1C (i.e. 7mA).

[0201] 3) Rate test of lithium metal battery after 200 cycles

[0202] The prepared stack cell was set to an ambient temperature of 25°C, and 0.2C (i.e., 14 mA) charging and 1C (i.e., 70 mA) discharging were used to perform 200 cycles of charge-discharge. Then, a rate test was performed, 0.2C (i.e., 14 mA) charging and 0.2C (i.e., 14 mA), 0.5C (i.e., 35 mA), 1C (i.e., 70 mA), 2C (i.e., 140 mA), and 4C (i.e., 280 mA) discharging were used to perform one cycle of charge-discharge. The cut-off voltages of the charge-discharge were set to 4.3V and 2.8V, respectively, and the charging process used a constant current-constant voltage charging method, and the capacity under 4C discharging was used as the discharge capacity after 200 cycles to evaluate the rate performance of the lithium metal battery. Specifically, after 0.2C constant current charging reached the cut-off voltage of 4.3V, constant voltage charging at 4.3V was used until the current decayed to 0.1C (i.e., 7 mA).

[0203] The test results are shown in Table 2.

[0204] As can be seen from Table 2, compared with Example 1-5 and Comparative Example 1, it can be seen that the carboxylated graphene quantum dots can effectively improve the cycle performance and rate performance in the later stage of the lithium metal battery. The reason is that: the negative electrode plate in the cell has less electrolyte by-product accumulation on the surface, and the polarization deterioration is small, so the initial rate performance of the examples and the comparative example is basically the same; at the same time, the content of the carboxylated graphene quantum dots can be selected as 0.1 mg / mL.

[0205] As can be seen from Example 6-10 and Comparative Example 1, the different types of carbon quantum dots used in the application are also beneficial to the electrochemical performance of the lithium metal battery, and can improve the cycle performance and rate performance of the lithium metal battery.

[0206] As can be seen from Example 11-18 and Comparative Example 1, the carbon quantum dots used in the application have good compatibility with a variety of local high-concentration electrolytes, and can ensure the long cycle and high rate work of the lithium metal battery.

[0207] As can be seen from Example 19-20 and Example 1, the negative electrode plate containing the carbon quantum dots is matched with different types of local high-concentration electrolytes containing the carbon quantum dots, which have good compatibility, improve the cycle performance and high rate of the lithium metal battery, and improve the electrochemical performance of the lithium metal battery.

[0208] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A lithium metal battery cell, comprising an electrolyte;The electrolyte comprises a lithium salt, carbon quantum dots, an ether solvent for dispersing and / or dissociating the lithium salt, and a diluent for diluting the ether solvent;The lithium salt is immiscible with the diluent.

2. The lithium metal battery cell of claim 1, wherein, The electrolyte meets one or more of the following conditions: 1) The concentration of the carbon quantum dots in the electrolyte is 0.01 mg / mL to 2 mg / mL; 2) The mass percentage of the lithium salt in the electrolyte is 20% to 28%.

3. The lithium metal battery cell of claim 1 or 2, wherein, The electrolyte meets one or more of the following conditions: 1) The concentration of the carbon quantum dots in the electrolyte is 0.1 mg / mL to 1 mg / mL; 2) The mass percentage of the lithium salt in the electrolyte is 24% to 25%.

4. The lithium metal battery cell of any one of claims 1-3, wherein, The molar ratio of the lithium salt, the ether solvent and the diluent is 1:(0.4-3):(1-5).

5. The lithium metal battery cell of any one of claims 1-4, wherein, The molar ratio of the lithium salt, the ether solvent and the diluent is 1:(1.2-2):(3-3.5).

6. The lithium metal battery cell of any one of claims 1-5, wherein, The electrolyte meets one or more of the following conditions: 1) The carbon quantum dots include one or more of graphene quantum dots, graphene oxide quantum dots, fluorinated graphene quantum dots, chlorinated graphene quantum dots, carboxylated graphene quantum dots, hydroxylated graphene quantum dots and aminated graphene quantum dots; 2) The lithium salt includes one or more of lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bisoxalate borate, lithium difluorobisoxalate borate, lithium difluorobisoxalate phosphate and lithium tetrafluorobisoxalate phosphate; 3) The ether solvent includes one or more of diethyl ether, dipropyl ether, ethyl propyl ether, methyl butyl ether, dibutyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol methyl ethyl ether, propylene glycol diethyl ether, butanediol dimethyl ether, butanediol methyl ethyl ether, butanediol diethyl ether, tetrahydrofuran, 3-methyl tetrahydrofuran, 1,3-dioxolane, tetrahydropyran, 1,3-dioxane and 1,4-dioxane. 4) the diluent comprises one or more of benzene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluoromethylbenzene, trifluoromethoxybenzene, decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-dimethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(difluoromethoxy)ethane, 1,2-bis(trifluoromethoxy)ethane, 1,2-diethoxy-1,1,2,2-tetrafluoroethane, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, bis(2,2-difluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

7. The lithium metal battery cell of any one of claims 1-6, wherein, The electrolyte satisfies one or more of the following conditions: 1) the conductivity of the electrolyte is 1 mS / cm to 10 mS / cm; 2) the viscosity of the electrolyte is 1 mPa-s to 10 mPa-s.

8. The lithium metal battery cell of any one of claims 1-7, wherein, The electrolyte satisfies one or more of the following conditions: 1) the conductivity of the electrolyte is 2 mS / cm to 8 mS / cm; 2) the viscosity of the electrolyte is 1.5 mPa-s to 8.5 mPa-s.

9. The lithium metal battery cell of any one of claims 1-8, wherein, The lithium metal battery cell comprises a negative electrode sheet, the negative electrode sheet comprises a composite lithium layer, the composite lithium layer comprises lithium metal and additional carbon quantum dots, the lithium metal is a continuous phase, and the carbon quantum dots are a dispersed phase.

10. The lithium metal battery cell of claim 9, wherein, The composite lithium layer satisfies one or more of the following conditions: 1) the mass content of the carbon quantum dots in the composite lithium layer is 0.01% to 10%; 2) the thickness of the composite lithium layer is 0.2 to 100 microns.

11. The lithium metal battery cell of claim 9 or 10, wherein, The composite lithium layer satisfies one or more of the following conditions: 1) the mass content of the carbon quantum dots in the composite lithium layer is 0.5% to 2%; 2) the thickness of the composite lithium layer is 5 to 20 microns.

12. The lithium metal battery cell of any one of claims 9-11, wherein, The negative electrode sheet comprises a negative electrode current collector and the composite lithium layer disposed on at least one side of the negative electrode current collector.

13. An electrolyte for a lithium metal battery cell, comprising a lithium salt, carbon quantum dots, an ether solvent for dispersing and / or dissociating the lithium salt, and a diluent for diluting the ether solvent, wherein the lithium salt and the diluent are immiscible.

14. A battery device, wherein, A lithium metal battery cell according to any one of claims 1 to 12 or a battery cell prepared by the electrolyte of claim 13.

15. An electrical device, comprising: A battery device according to claim 14.

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