Lithium metal battery cell, negative electrode plate and manufacturing method therefor, battery apparatus and electrical apparatus

Abstract

Provided in the present application are a lithium metal battery cell, a negative electrode plate and a manufacturing method therefor, a battery apparatus, and an electrical apparatus. The lithium metal battery comprises a negative electrode plate; the negative electrode plate comprises a composite lithium layer; the composite lithium layer comprises lithium metal and carbon quantum dots, the lithium metal being a continuous phase, and the carbon quantum dots being a dispersed phase.

Description

Lithium metal battery cell, negative electrode sheet and preparation method thereof, battery device and electric device

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202411370949.0, filed on September 29, 2024, entitled “Lithium metal battery cell, negative electrode sheet and preparation method thereof, battery device and electric 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, a negative electrode sheet and a preparation method thereof, a battery device and an electric device. BACKGROUND

[0004] With the rapid development of lithium secondary batteries in the fields of electric vehicles, electric aviation, etc., the public's demand for energy density of battery products is increasing due to the space limitations of application scenarios. Mainly because the lithium metal anode of the lithium secondary battery has a high theoretical specific capacity of 3860 mAh g-1 and a low oxidation-reduction potential, for example, -3.04 V vs. standard hydrogen electrode, the energy density of the lithium metal battery can exceed 500 Wh / kg, which is one of the most potential next-generation battery systems. With the application and promotion of lithium metal battery cells, their comprehensive performance is attracting more and more attention, for example, a large amount of lithium dendrites will be generated during the charging and discharging of the metal lithium, 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 present application provides a lithium metal battery cell, the reliability, kinetic performance and cycle capacity retention rate of which are improved. The present application also provides a negative electrode sheet and a preparation method thereof, which can achieve the excellent effects of the above-mentioned lithium metal battery cell. The battery device and the electric 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, comprising a negative electrode sheet; the negative electrode 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.

[0008] 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. The carbon quantum dots uniformly dispersed in the lithium metal can serve as uniform heterogeneous nucleation sites, can reduce the nucleation potential of lithium ions, are conducive to the deposition and solvation of lithium ions, can reduce the risk of lithium dendrite growth, and improve the reliability 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 serve as a rapid diffusion channel for lithium ions, and can improve the ion conduction ability of the SEI film, which is conducive to improving the kinetic performance of the lithium metal battery.

[0009] On the other hand, the carbon quantum dots uniformly dispersed in the lithium metal can be uniformly attached to the ultra-thin solid electrolyte film (SEI film) formed in the 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.

[0010] In addition, in the later stage of the electrochemical cycle of the lithium metal battery, the surface of the lithium metal negative pole piece still contains uniform carbon quantum dots, which can act on the entire life cycle of the lithium metal battery to regulate the nucleation and deposition of lithium metal at the interface.

[0011] 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, are conducive to the deposition and solvation of lithium ions, improve the reliability of the lithium metal battery, and the carbon quantum dots are uniformly attached to the SEI film to improve the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0012] 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.

[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. 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.

[0014] For example, the carboxyl group in the carboxylated graphene quantum dots can endow the graphene quantum dots with strong electronegativity, so that the graphene quantum dots have high lithium ion affinity, which is conducive to improving the kinetic performance of the lithium metal battery.

[0015] 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 can still uniformly deposit lithium due to repeated lithium deposition and stripping during the charging and discharging process, thereby improving the cycle life and reliability of the lithium metal battery.

[0016] 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.

[0017] In some optional embodiments, the negative electrode tab includes a negative current collector and a composite lithium layer arranged on at least one side of the negative current collector. Therefore, such a negative electrode tab is beneficial to balance the energy density and kinetic performance of the lithium metal battery.

[0018] In some optional embodiments, the electrolyte includes a lithium salt, additional carbon quantum dots, an organic solvent, and a dispersant.

[0019] In the embodiments of the present application, the electrolyte containing a lithium salt, an ether solvent, and a dispersant is polarized at the interface between the negative electrode tab and the solid electrolyte film during the later stage of electrochemical cycling of the lithium metal battery. The SEI film is continuously destroyed and reformed, resulting in poor cycle capacity stability and kinetic performance of the lithium metal battery. The additional carbon quantum dots dispersed in the electrolyte are a zero-dimensional material and participate in the formation of the SEI film. The carbon quantum dots have abundant edge defects and can serve as a fast diffusion channel for lithium ions, thereby improving the ionic conductivity of the SEI film, promoting the deposition of lithium ions through the SEI film and uniformly on the negative electrode tab, and improving the above-mentioned polarization phenomenon, thereby improving the cycle capacity stability and kinetic performance of the lithium metal battery.

[0020] In some optional embodiments, the mass concentration of the carbon quantum dots in the electrolyte is 0.01 mg / mL-2 mg / mL. The content of the carbon quantum dots is uniformly attached to the ultra-thin SEI film, thereby improving the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0021] In some optional embodiments, the mass percentage content of the lithium salt in the electrolyte is 20%-28%. The mass content of the lithium salt in the above range can reduce unnecessary side reactions that lose lithium, reduce the formation of "dead lithium" in the battery, and thereby improve the cycle capacity retention rate of the lithium metal battery; 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.

[0022] In some optional embodiments, the mass percentage content of the lithium salt in the electrolyte is 24%-25%.

[0023] 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 deposition of lithium ions through the SEI film and on the negative electrode sheet, and also improve the above polarization phenomenon, thereby further improving the cycle capacity stability and kinetic performance of the lithium metal battery.

[0024] In some optional embodiments, the mass ratio of the lithium salt, the ether solvent and the dispersant is 1:(0.4-3):(1-5). Controlling the mass ratio of the lithium salt, the ether solvent and the dispersant 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 sheet and improves the cycle capacity retention rate of the lithium metal battery. It can also promote the uniform deposition of lithium ions on the negative electrode surface, inhibit the generation of dendrites, and improve the reliability of the lithium metal battery.

[0025] In some optional embodiments, the mass ratio of the lithium salt, the ether solvent and the dispersant is 1:(1.2-2):(3-3.5). Therefore, the cycle capacity retention rate and the reliability of the lithium metal battery can be further improved.

[0026] 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.

[0027] 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.

[0028] In some alternative embodiments, the dispersant includes 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 (TTE), 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, bis(1,1,2,2-tetrafluoroethyl) ether.

[0029] In a second aspect, the embodiments of the present application provide a negative electrode sheet for a lithium metal battery, including a composite lithium layer, the composite lithium layer including lithium metal and carbon quantum dots, the lithium metal being a continuous phase, and the carbon quantum dots being a dispersed phase.

[0030] In the embodiments of the present application, the composite lithium layer of the negative electrode sheet includes lithium metal material and carbon quantum dots, the carbon quantum dots uniformly dispersed in the lithium metal serve as uniform heterogeneous nucleation sites, can reduce the nucleation potential of lithium ions, are conducive to the deposition and solvation of lithium ions, can reduce the risk of lithium dendrite growth, and improve the reliability of the lithium metal battery; in the process of electrochemical cycling of the lithium metal battery, as the lithium metal is consumed, the carbon quantum dots participate in the formation of SEI film in situ, can serve as a rapid diffusion channel for lithium ions, and improve the ion conduction capability of the SEI film, which is conducive to improving the kinetic performance of the lithium metal battery.

[0031] On the other hand, the carbon quantum dots uniformly dispersed in the lithium metal can be subsequently attached to an ultra-thin SEI film, 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.

[0032] In a third aspect, the embodiments of the present application provide a preparation method of a negative electrode sheet for a lithium metal battery, including:

[0033] heating the lithium metal and the carbon quantum dots in an inert atmosphere to form a flow phase of the lithium metal;

[0034] dispersing the carbon quantum dots in the lithium metal in a flow phase to obtain a uniformly dispersed mixture;

[0035] cold-pressing the mixture to obtain a composite lithium layer.

[0036] In the present embodiment, the melting point of lithium metal is generally 180.5℃, 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 in a flow phase, the carbon quantum dots can be uniformly dispersed in the lithium metal to form a composite lithium layer.

[0037] The carbon quantum dots uniformly dispersed in the lithium metal can also reduce the nucleation potential of lithium ions as uniformly distributed heterogeneous nucleation sites, which is conducive to the deposition and solvation of lithium ions, can reduce the risk of lithium dendrite growth, and improves the reliability of the lithium metal battery. In the process of 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 rapid diffusion channel for lithium ions, and improve the ion conduction ability of the SEI film, which is conducive to improving the kinetic performance of the lithium metal battery.

[0038] In a fourth aspect, the present application provides a battery device, which comprises the lithium metal battery of the first aspect or a battery cell made of the negative electrode tab of the second aspect or prepared by the preparation method of the third aspect.

[0039] In a fifth aspect, the present application provides a power utilization device, which comprises the battery device of the fourth aspect.

[0040] The power utilization device of the present application comprises the battery device of the fourth aspect of the present application, and thus at least has the advantages corresponding to the negative electrode tab lithium metal battery cell. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings.

[0042] FIG. 1 shows a schematic diagram of an embodiment of the lithium metal battery cell of the present application.

[0043] FIG. 2 shows an exploded schematic diagram of an embodiment of the lithium metal battery cell shown in FIG. 1.

[0044] FIG. 3 shows a schematic diagram of a battery pack as a whole according to an embodiment of the present application.

[0045] FIG. 4 shows an exploded schematic diagram of a battery pack according to an embodiment of the present application.

[0046] FIG. 5 shows a schematic diagram of an embodiment of an electric device including the lithium metal battery cell of the present application as a power source.

[0047] In the drawings, the drawings are not necessarily drawn to actual scale. Reference numerals are explained below: 1, battery pack, 2, upper case, 3, lower case, 4, battery module, 5, lithium metal battery cell. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the lithium metal battery cell, electrolyte, battery device, and electric device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters well known in the art, repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0049] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" represents a shorthand manner of describing each and every numerical value that is contained within the range, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand manner of describing those numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] If not specifically stated, 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.

[0051] If not specifically stated, 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.

[0052] 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.

[0053] 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.

[0054] If not otherwise specified, the term “active ion” in the present application refers to an ion that can be inserted and de-inserted between the positive and negative electrodes of a lithium metal battery cell, including but not limited to lithium ion and the like.

[0055] “Multiple” or “a plurality of” appearing in the present application refers to two or more (including two). “Several” or “a plurality of” appearing in the present application refers to two, three or more (including two).

[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 lithium metal battery cells, battery modules, or battery packs, 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, in parallel, or in a hybrid manner through a busbar component.

[0058] In some optional embodiments, the lithium metal battery cell assembly is generally 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 optional embodiments, the battery device can be a battery pack, which can include a box and one or more lithium metal battery cell assemblies housed in the box. In some optional embodiments, the box can be part of the chassis structure of the vehicle. For example, part of the box can be at least part of the floor of the vehicle, or part of the box can be at least part of the cross beam and the 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 box by fixing the battery module in the box.

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

[0062] The lithium metal battery cell is the smallest unit that makes up the battery device, which can independently realize the function of charging and discharging. 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 shown in FIG. 1, the lithium metal battery cell 5 is in the shape of a cuboid as an example.

[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 optional 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 optional embodiments, the lithium metal battery cell can be assembled into a battery module, and the number of lithium metal battery cells contained in the battery module can be multiple, and the specific number 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] Optionally, the battery module 4 can also include a housing having an accommodation space, and the multiple lithium metal battery cells 5 are accommodated in the accommodation space.

[0066] In some optional 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. 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 structure or a stacked structure, and the embodiments of the present application are not limited in this regard. 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 uncontrollable deposition of metal lithium of the negative electrode in the lithium metal battery during charging and discharging process can cause lithium dendrite and low coulombic efficiency (CE) problems. If the linearly grown lithium dendrite is broken from the root during the dissolution process, this part of lithium is wrapped by the electrolyte to form "dead lithium" and is embedded into the bulk phase, causing the coulombic efficiency to decrease, which is not conducive to the performance of the lithium metal battery. In addition, the growth of lithium dendrite can also pierce the SEI film between the lithium metal negative electrode and the electrolyte, and then pierce the separator, which can cause short circuit of the battery and reduce the reliability of the lithium metal battery.

[0072] In view of this, the embodiments of the present application provide a lithium metal battery to solve the above problems.

[0073] [Negative electrode sheet]

[0074] In some optional embodiments, the negative electrode tab 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.

[0075] 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. The uniformly dispersed carbon quantum dots in the lithium metal serve as uniform heterogeneous nucleation sites, can reduce the nucleation potential of lithium ions, are conducive to the deposition and solvation of lithium ions, can reduce the risk of lithium dendrite growth, and improve the reliability 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 serve as a rapid diffusion channel for lithium ions, and improve the ion conduction ability of the SEI film, which is conducive to improving the kinetic performance of the lithium metal battery.

[0076] On the other hand, the carbon quantum dots uniformly dispersed in the lithium metal can be uniformly attached to the ultra-thin solid electrolyte film (SEI film) formed in the 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.

[0077] 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, are conducive to the deposition and solvation of lithium ions, improve the reliability of the lithium metal battery, and the carbon quantum dots are uniformly attached to the ultra-thin SEI film, improve the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0078] The mass content of the carbon quantum dots in the composite lithium layer can be observed by a scanning electron microscope to observe the distribution of the carbon quantum dots in the metal layer, and energy dispersive X-ray spectroscopy (EDS) can be used to determine the mass of the particles.

[0079] Alternatively, any value or range consisting of the combination 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%.

[0080] 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.

[0081] 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.

[0082] In some optional embodiments, the thickness of the composite lithium layer is 2-100 microns.

[0083] 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.

[0084] The thickness of the composite lithium layer is in the above-mentioned 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] In some optional embodiments, the thickness of the negative electrode tab can be 2-200 microns, optionally 6-120 microns, and optionally 140 microns.

[0089] The negative electrode current collector can be a metal material, and the material includes but is not limited to one or more of metal copper, nickel, lithium, iron, or stainless steel. It can be understood that any material of the negative electrode current collector can support the function of the composite lithium foil. In some optional embodiments, the negative electrode tab is the composite lithium layer, which can not include the negative electrode current collector.

[0090] In some optional embodiments, the thickness of the negative current collector can be 0-20 microns, and optionally 4-12 microns.

[0091] In some optional embodiments, the negative current collector comprises one or more of lithium element, lithium alloy.

[0092] In some optional embodiments, the negative current collector can comprise a metal foil, a three-dimensional porous current collector, or a composite current collector. As an example of the metal foil, a copper foil, a copper alloy foil, a nickel foil, a nickel alloy foil, an aluminum foil, or an aluminum alloy foil can be used. As an example of the three-dimensional porous current collector, a copper mesh, a nickel mesh, an aluminum mesh, a copper foam, a nickel foam, or an aluminum foam can be used. The composite current collector can comprise 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 comprise 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 comprise one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0093] The embodiments of the present application provide a preparation method of a negative electrode sheet for a lithium metal battery, comprising:

[0094] heating the lithium metal and the carbon quantum dots in an inert atmosphere to form a flow phase of the lithium metal;

[0095] dispersing the carbon quantum dots in the lithium metal of the flow phase to obtain a uniformly dispersed mixture;

[0096] cold-pressing the mixture to obtain a composite lithium layer.

[0097] In the embodiments, the melting point of the lithium metal is generally 180.5℃, and the melting point of the carbon quantum dots is generally much higher than that of the lithium metal. The carbon quantum dots can be uniformly dispersed in the lithium metal by dispersing the carbon quantum dots in the lithium metal of the flow phase, so as to form the composite lithium layer. The preparation method of the present application is simple, easy to operate, good in repeatability, low in cost, and pollution-free to the environment, and is suitable for industrial production.

[0098] 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, can reduce the risk of lithium dendrite growth, and improves the reliability of the lithium metal battery; the carbon quantum dots uniformly dispersed in the lithium metal can be subsequently attached to the ultra-thin SEI film, 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; in the process of 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 serve as a rapid 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.

[0099] In some optional embodiments, the inert atmosphere can include inert gases such as nitrogen, argon, etc.

[0100] In some optional embodiments, the target temperature of heating can be 180.5-220℃. 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.

[0101] In some optional embodiments, before the cold-pressed mixture is obtained, the method further includes: cooling the mixture.

[0102] In some optional embodiments, the cold-pressed mixture to obtain the composite lithium layer specifically includes: cold-pressing the mixture on a precision roller press to obtain the composite lithium layer. The gap of the precision roller press can be 2-100 microns.

[0103] In some optional embodiments, the preparation method of the negative electrode sheet further includes: cold-pressing the composite lithium layer and the negative electrode current collector to obtain the negative electrode sheet.

[0104] The preparation method of the present application is simple, easy to operate, has good repeatability, low cost, and no pollution to the environment, and is suitable for industrial production.

[0105] [Electrolyte]

[0106] In some optional embodiments, the electrolyte includes a lithium salt, additional carbon quantum dots, an organic solvent, and a dispersant, wherein the organic solvent includes an ether solvent.

[0107] In the embodiments of the present application, after the electrolyte containing lithium salt, ether solvent and dispersant is electrochemically cycled in the lithium metal battery, there is a certain polarization phenomenon at the interface between the negative electrode sheet and the electrolyte, and the electrolyte film (SEI film) may be continuously destroyed and reformed, which affects the cycle capacity stability and kinetic performance of the lithium metal battery. The carbon quantum dots dispersed in the electrolyte are a kind of zero-dimensional materials and participate in the formation of SEI film. The carbon quantum dots have rich edge defects and can be used as a fast diffusion channel for lithium ions, which can improve the ionic conductivity of SEI film, promote the deposition of lithium ions through SEI film and on the negative electrode sheet, and also improve the above-mentioned polarization phenomenon, thereby improving the cycle capacity stability and kinetic performance of the lithium metal battery. 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 SEI film, thereby improving the cycle capacity retention rate and kinetic performance of the lithium metal battery.

[0108] It can be understood that the ether solvent can be used to disperse and / or dissociate the lithium salt; the dispersant can be used to disperse or dilute the ether solvent to form an organic solvent for dissolving or dispersing the lithium salt; and the lithium salt and the dispersant can not be mutually soluble.

[0109] Alternatively, the mass concentration of carbon quantum dots in the electrolyte can be any value or a range consisting of any values in 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.

[0110] 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 SEI film, improve the ionic conductivity of SEI film, promote the deposition of lithium ions through SEI film and 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.

[0111] In some optional embodiments, the mass percentage of lithium salt in the electrolyte is 20% to 28%.

[0112] Optionally, the mass percentage content of the lithium salt in the electrolyte can be any value or a range composed of any value in 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%. In some optional embodiments, the mass percentage content of the lithium salt in the electrolyte is 24% to 25%

[0113] The lithium salt mass content in the above range can reduce unnecessary side reaction loss of lithium, reduce the formation of "dead lithium" in the battery, and further improve the cycle capacity retention rate of the lithium metal battery; 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.

[0114] In some optional embodiments, the molar ratio of the lithium salt, the ether solvent and the dispersant is 1:(0.4-3):(1-5).

[0115] Optionally, the molar ratio of the lithium salt, the ether solvent and the dispersant is any ratio or a range composed of 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. Controlling the molar amount of the lithium salt, the ether solvent and the dispersant 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 sheet, and improves the cycle capacity retention rate of the lithium metal battery. 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.

[0116] In some optional embodiments, the molar ratio of the lithium salt, the ether solvent and the dispersant is 1:(1.2-2):(3-3.5). Therefore, the cycle capacity retention rate and the reliability of the lithium metal battery can be further improved.

[0117] 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 difluorooxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0118] 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, butylene glycol dimethyl ether, butylene glycol methyl ethyl ether, butylene glycol diethyl ether, tetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, tetrahydropyran, 1,3-dioxane, 1,4-dioxane.

[0119] In some optional embodiments, the dispersant includes 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 (TTE), 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, bis(1,1,2,2-tetrafluoroethyl) ether.

[0120] In some optional embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and / or an additive capable of improving certain performance of the battery cell, such as an additive capable of improving overcharge / fast charge performance of the battery cell, an additive capable of improving high-temperature performance of the battery cell, an additive capable of improving low-temperature performance of the battery cell, and / or the like.

[0121] Methods for preparing electrolyte solutions are known. For example, an electrolyte salt (lithium salt), a solvent, and an optional additive can be mixed uniformly to obtain an electrolyte solution. The order in which the materials are added during the preparation process is not particularly limited, and the materials can be added simultaneously or in batches.

[0122] The components in the electrolyte 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.

[0123] For example, infrared spectroscopy can be used to determine the compounds contained in the electrolyte, such as the characteristic peak of the sulfur-oxygen double bond in the sulfoxide compound at 1060 cm -1 -1040 cm -1 By high-resolution gas chromatography-high-resolution mass spectrometry, different components in the electrolyte can be separated and high-precision molecular weights can be obtained, so that the atomic composition can be determined; and then the specific molecular structure of each component can be confirmed by the spectrum results of nuclear magnetic resonance.

[0124] [Positive electrode sheet]

[0125] In some alternative embodiments, the positive electrode sheet includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector, the positive film layer including a positive active material. For example, the positive current collector has two surfaces opposite in the thickness direction of the positive current collector, and the positive film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0126] The type of positive active material can be selected according to the type of lithium metal battery cell, which is not limited in the embodiments of the present application.

[0127] For example, the positive current collector has two surfaces opposite in the thickness direction of the positive current collector, and the positive active material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0128] For example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, surface-treated metals, including but not limited to stainless steel, copper, aluminum, nickel, nickel, titanium, or silver, and the like can be used. 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, etc.) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0129] 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 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 of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0130] Examples of the lithium transition metal oxide can include, but are not limited to, at least one of 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 Mn 0.1 O2 (which can also 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 compound refers to a substance obtained by a modification means such as doping or coating on the basis of the above-mentioned substance.

[0131] The battery cell will be accompanied by Li deintercalation and consumption during charging and discharging process, and the molar content of Li is different when the battery cell is discharged to different states. In the enumeration of the positive 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 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 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 crystal lattice will cause the molar content of O to change, and the actual molar content of O will also appear to float.

[0132] In some optional embodiments, the positive electrode can adopt a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When the foamed metal is used as the positive electrode, the surface of the foamed metal can not be provided with the positive active material, of course, the positive active material can also be provided. As an example, the positive active material is filled or / and deposited in the foamed metal.

[0133] In some optional embodiments, the positive electrode film layer further optionally comprises 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.

[0134] In some optional embodiments, the positive electrode film layer further optionally comprises 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 resin.

[0135] In some optional embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. As an example of the metal foil, an aluminum foil can be adopted. 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, 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).

[0136] The positive electrode film layer can be formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive active material, the optional conductive agent, the optional binder and any other components in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP), but is not limited thereto.

[0137] [separator]

[0138] In some embodiments, the electrode assembly further comprises a separator disposed between the positive electrode tab and the negative electrode tab.

[0139] 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 known porous structure separator film having good chemical stability and mechanical stability can be used.

[0140] 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. 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 layers can be the same or different, and are not particularly limited. The separator can be a separate component located between the positive and negative electrodes, or can be attached to the surface of the positive and negative electrodes. An inorganic particle coating, an organic particle coating, or an organic / inorganic composite coating can also be applied to the surface of the separator film.

[0141] In some embodiments, the separator is a solid-state electrolyte. The solid-state electrolyte is disposed between the positive electrode and the negative electrode, and functions to transport ions and separate the positive and negative electrodes.

[0142] The preparation method of a lithium metal battery cell is known. In some optional embodiments, the positive electrode tab, the separator film, the negative electrode tab, and the electrolyte can be assembled to form a lithium metal battery cell. As an example, the positive electrode tab, the separator film, and the negative electrode tab can be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly can be placed in an outer package, and after drying, the electrolyte can be injected. The lithium metal battery cell can be obtained after the processes of vacuum packaging, standing, formation, shaping, etc. A plurality of lithium metal battery cells can be further 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 further 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.

[0143] Electric device

[0144] The embodiments of the present application provide an electric device, which comprises the battery device described above.

[0145] Lithium metal battery cells can be used as power sources for electric devices, and can also be used as energy storage units for electric devices. The electric devices can be, but are not limited to, mobile devices (e.g., cell phones, tablets, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0146] The electric devices can select lithium metal battery cells, lithium metal battery cell modules, or lithium metal battery cell packs according to their usage requirements.

[0147] 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, a lithium metal battery cell pack or a lithium metal battery cell module can be used.

[0148] The electric device as another example can be a cell phone, a tablet, a laptop, etc. The electric device usually requires thin and light, and a lithium metal battery cell can be used as a power source.

[0149] Embodiments

[0150] The following examples more specifically describe the present disclosure, which are merely illustrative and not restrictive, since various modifications and changes in the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further purification, and the instruments used in the examples are commercially available.

[0151] Example 1

[0152] Preparation of the negative electrode tab: a. Lithium metal and carboxylated graphene quantum dots were placed in a reactor under argon protection in a mass ratio of 99.5:0.5, heated to 185°C, and uniformly stirred at constant temperature;

[0153] b. The aforementioned stirred composite lithium metal was cooled;

[0154] c. The aforementioned cooled composite lithium metal was cold-pressed into a 20-micron composite lithium foil on a precision roller press;

[0155] d. The composite lithium foil was roll-bonded with a 12-micron copper foil to form a negative electrode tab, and cut into a 41 mm x 51 mm rectangle for standby as a negative electrode tab.

[0156] Preparation of a lithium metal battery

[0157] Preparation of electrolyte: take lithium salt LiFSI, dimethyl ether (DME), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a molar ratio of 1:1.2:3, mix them well under stirring to form a colorless transparent electrolyte.

[0158] Preparation of positive electrode sheet: mix positive active material lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), conductive agent acetylene black, 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 positive electrode slurry (solid content is 70%); coat the positive electrode slurry with a loading of 12.5 mg / cm 2 on both sides of the positive current collector, i.e. aluminum foil, dry at room temperature, then transfer to an oven for further drying, and then cut into a 40 mm x 50 mm rectangle as a positive electrode sheet.

[0159] Separator film: select a polyethylene porous film and cut it into a 45 mm x 55 mm rectangle.

[0160] Battery assembly: take one piece of cut positive electrode and two pieces of cut negative electrode, use the above-mentioned separator film to separate the positive and negative electrodes, and wrap them in an aluminum plastic film bag to form a stacked dry battery. Inject 0.3 g of the above-mentioned 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 70 mAh.

[0161] Examples 2-5

[0162] Examples 2-5 are consistent with Example 1, except that the mass content of carbon quantum dots in the composite lithium layer is different, as shown in Table 1.

[0163] Examples 6-10

[0164] Examples 6-10 are consistent with Example 1, except that the types of carbon quantum dots in the composite lithium layer are different, as shown in Table 1.

[0165] Examples 11 to 13

[0166] Examples 11 to 13 are consistent with Example 1, except that the thickness of the composite lithium layer is different, as shown in Table 1.

[0167] Example 14

[0168] Example 14 is consistent with Example 1, except that the negative electrode sheet does not have a negative current collector aluminum foil, only a composite lithium layer, and the thickness of the composite lithium layer is 20 microns. See Table 1 for details.

[0169] Examples 15-16

[0170] Examples 15-16 are consistent with Example 1, except for the difference in the composition of the electrolyte. In Examples 15-16, carbon quantum dots are added to the electrolyte, and the mass content of the carbon quantum dots in the electrolyte is 0.01 mg / mL and 2 mg / mL, respectively. See Table 1.

[0171] Comparative Example 1

[0172] The battery is prepared and tested in the same manner as in Example 1, except that the lithium metal anode is a 20-micron pure lithium foil combined with a 12-micron copper foil, and no carbon quantum dots are added.

[0173] Test Section

[0174] 1) Long cycle test of lithium metal battery

[0175] Take the above prepared stack cell, 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 uses constant current-constant voltage charging method, specifically, when the 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 decays to 80% of the first cycle discharge capacity, the cycle life of the lithium metal battery is considered.

[0176] 2) Initial rate test of lithium metal battery

[0177] Take the above prepared stack cell, set the ambient temperature to 25°C, use 0.2C (i.e. 14mA) charging, 0.2C (i.e. 14mA), 0.5C (i.e. 35mA), 1C (i.e. 70mA), 2C (i.e. 140mA), 4C (i.e. 280mA) discharging for one charge-discharge cycle. The cut-off voltage of charge and discharge is set to 4.3V and 2.8V respectively, and the charging process uses constant current-constant voltage charging method, and the capacity under 4C discharging rate is taken as the initial discharge capacity. Specifically, when the 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).

[0178] 3) Rate test of lithium metal battery after 200 cycles

[0179] The prepared laminated cell was taken, the ambient temperature was set to 25 DEG C, 0.2C (i.e. 14 mA) charging, 1C discharging (i.e. 70 mA) was used for 200 cycles of charge-discharge cycle. Then the rate test was carried out, the charging rate was 0.2C (i.e. 14 mA), the discharge rate was 0.2C (i.e. 14 mA), 0.5C (i.e. 35 mA), 1C (i.e. 70 mA), 2C (i.e. 140 mA), 4C (i.e. 280 mA) respectively. The cut-off voltage of charge-discharge was set to 4.3V and 2.8V respectively, and the charging process used constant current-constant voltage charging method, the capacity under 4C discharge rate was taken as the discharge capacity after 200 cycles, so as to evaluate the rate performance of lithium metal battery. Specifically, after 0.2C constant current charging reached the cut-off voltage 4.3V, constant voltage charging of 4.3V was used instead, until the current decayed to 0.1C (i.e. 7 mA).

[0180] The test results are shown in Table 1.

[0181] As can be seen from Table 1, compared with Comparative Example 1, the lithium metal battery of Examples 1-10 has improved cycle life and rate performance in the later cycle stage by adding different types and amounts of carbon quantum dots in the composite lithium layer. As can be seen from Examples 1-5, the effect is deviated to a certain extent because the content of carboxylated graphene quantum dots is too low to provide enough nucleation sites. When the content of carboxylated graphene quantum dots is 0.5%, enough nucleation sites are provided to improve the cycle life and rate performance of lithium metal battery in the later cycle stage.

[0182] As can be seen from Examples 11-13 and Example 1, the cycle life of lithium metal battery is affected by the thickness of the composite lithium layer. The thicker the composite lithium foil, the longer the cycle life of the battery, but the thicker the thickness, the energy density of the cell may decrease. In general, the performance is best when the thickness of the composite lithium foil is 20 microns.

[0183] As can be seen from Example 14 and Example 1, the cycle life of lithium metal battery is affected by removing the negative electrode current collector from the negative electrode lithium layer of the negative electrode tab.

[0184] As can be seen from Examples 15-16 and Example 1, the cycle life of lithium metal battery is improved by adding carbon quantum dots in the electrolyte, but the rate performance of lithium metal battery in the later cycle stage is also affected to a certain extent.

[0185] 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, wherein, The negative electrode 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.

2. The lithium metal battery of claim 1, wherein, The mass content of the carbon quantum dots in the composite lithium layer is 0.01% to 10%.

3. The lithium metal battery of claim 1 or 2, wherein, The mass content of the carbon quantum dots in the composite lithium layer is 0.5% to 2%.

4. The lithium metal battery of any one of claims 1-3, wherein, The carbon quantum dots comprise 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.

5. The lithium metal battery of any one of claims 1-4, wherein, The thickness of the composite lithium layer is 2 to 100 microns.

6. The lithium metal battery of any one of claims 1-5, wherein, The thickness of the composite lithium layer is 10 to 20 microns.

7. The lithium metal battery of any one of claims 1-6, wherein, The negative electrode sheet comprises a negative electrode current collector and the composite lithium layer arranged on at least one side of the negative electrode current collector.

8. The lithium metal battery of any one of claims 1-7, wherein, The lithium metal battery comprises an electrolyte, the electrolyte comprises a lithium salt, additional carbon quantum dots, an organic solvent, and a dispersant, the organic solvent comprises an ether solvent.

9. The lithium metal battery of claim 8, wherein, The electrolyte satisfies one or more of the following conditions: 1) the mass 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 amount-of-substance ratio of the lithium salt, the ether solvent, and the dispersant is 1:(0.4 to 3):(1 to 5).

10. The lithium metal battery of claim 8 or 9, wherein, The electrolyte satisfies one or more of the following conditions: 1) the mass 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%; 3) the amount-of-substance ratio of the lithium salt, the ether solvent, and the dispersant is 1:(1.2 to 2):(3 to 3.5).

11. The lithium metal battery of any one of claims 8-10, wherein, The electrolyte satisfies one or more of the following conditions: 1) the lithium salt comprises one or more of lithium bisfluorosulfonylimide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bisoxalateborate, lithium difluorobisoxalatephosphate, and lithium tetrafluorobisoxalatephosphate; 2) the ether solvent comprises 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, butylene glycol dimethyl ether, butylene glycol methyl ethyl ether, butylene glycol diethyl ether, tetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxolane, tetrahydropyran, 1,3-dioxane, and 1,4-dioxane. 3) the dispersant 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, bis(1,1,2,2-tetrafluoroethyl) ether.

12. A negative electrode sheet for a lithium metal battery, comprising a composite lithium layer, the composite lithium layer comprising lithium metal and carbon quantum dots, the lithium metal being a continuous phase, and the carbon quantum dots being a dispersed phase.

13. A method for preparing a negative electrode sheet for a lithium metal battery, comprising: heating lithium metal and carbon quantum dots in an inert atmosphere to form the lithium metal into a flowing phase; dispersing carbon quantum dots in the lithium metal of the flowing phase to obtain a mixture; cold-pressing the mixture to obtain a negative electrode sheet comprising a composite lithium layer.

14. A battery device, wherein, A battery cell comprising the lithium metal battery of any one of claims 1-11 or prepared by the negative electrode sheet of claim 12 or the method of claim 13.

15. An electrical device, comprising: A battery device comprising the battery cell of claim 14.

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