A lithium metal battery

Abstract

The application relates to the field of battery materials and discloses a lithium metal battery. The lithium metal battery provided by the application comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; the negative electrode sheet comprises a current collector at least one side surface and an active layer arranged on the current collector, the current collector comprises a foil and a protective layer arranged on at least one side surface of the foil; the thickness of the active layer is d mu m, and d satisfies 30 <= d <= 100; the electrolyte comprises an organic solvent A and a compound C, and the mass percentage of the organic solvent A in the electrolyte is a %, and a satisfies 30 <= a <= 80. Through mutual cooperation of the organic solvent A, the protective layer and the compound C, the heat runaway problem of the battery can be effectively improved, and the cycle rate performance of the battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery materials, in particular to a lithium metal battery. BACKGROUND

[0002] At present, in order to expand the capacity of the lithium metal battery, the thickness of the active layer in the negative electrode sheet can be increased, but when the thickness of the active layer in the negative electrode sheet is too thick, the transmission distance of lithium ions in the electrode will be significantly increased, the ion conductivity will be reduced, and the expansion of the lithium metal negative electrode will be aggravated, the side reaction will be increased, and then the heat production and accumulation will be caused, and the safety problems such as thermal runaway caused by overheating will be easily caused.

[0003] For the safety problem of thermal runaway, the related technical reports disclose that the safety performance of the lithium metal battery can be improved by doping and coating the positive electrode material, reducing the heat shrinkage rate of the separator, increasing the thickness of the separator or optimizing the composition of the electrolyte, thereby improving the safety performance of the lithium metal battery.

[0004] However, the above technical solutions disclosed at present cannot significantly improve the problem of thermal runaway while ensuring the capacity of the battery. Therefore, how to significantly improve the thermal runaway while effectively improving the capacity of the battery and ensuring the safety is an urgent technical problem to be solved by the person skilled in the art. SUMMARY

[0005] The present application provides a lithium metal battery, which aims to solve the problem that the existing lithium metal battery cannot ensure the capacity of the battery while considering safety to some extent.

[0006] The present application provides a lithium metal battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0007] The negative electrode sheet comprises a current collector and an active layer arranged on at least one side surface of the current collector, and the current collector comprises a foil and a protective layer arranged on at least one side surface of the foil.

[0008] The thickness of the active layer is d μm, and d satisfies 30≤d≤100.

[0009] The electrolyte comprises an organic solvent A and a compound C, and the mass fraction of the organic solvent A in the electrolyte is a%, and a satisfies 30≤a≤80.

[0010] The organic solvent A comprises at least one of the structures shown in formula 1,

[0011] Formula 1: Wherein, R1, R2, R3 are independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon group with carbon atom number of 1-8, hydrocarbon oxy group, and R2 and R3 can be connected to form a ring.

[0012] The compound C includes at least one of structures shown in formula 2,

[0013] Formula 2: wherein, R4 and R5 are independently selected from H, F-substituted or unsubstituted hydrocarbon group with carbon number of 1-10, and hydrocarbon oxy group.

[0014] In an optional embodiment, the organic solvent A includes at least one of structures shown in formula 1-1 to formula 1-8:

[0015]

[0016] And / or, the compound C includes at least one of structures shown in formula 2-1 to formula 2-8:

[0017]

[0018] And / or, the mass ratio of the compound C in the electrolyte is c%, c satisfies: 0

[0019] In an optional embodiment, the electrolyte further includes lithium salt B, the lithium salt B includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(trifluoromethylsulfonyl)imide;

[0020] Preferably, the mass ratio of the lithium salt B in the electrolyte is b%, b satisfies: 10

[0021] In an optional embodiment, 0.4

[0022] In an optional embodiment, the surface capacity of the negative electrode sheet is x mAh / cm 2 , x satisfies: 5

[0023] And / or, the tensile strength of the current collector is s MPa, s satisfies: 350

[0024] And / or, the thickness of the protective layer is y nm, y satisfies: 0

[0025] In an optional embodiment, the foil is copper foil;

[0026] And / or, the material of the protective layer comprises at least one of a metal oxide, a carbon-based material, and a conductive polymer.

[0027] Preferably, the carbon-based material can be selected from at least one of graphite, soft carbon, hard carbon, and graphene, the conductive polymer can be selected from one or more of polyimide, polyaniline, polyacrylamide, and polypyrrole, and the metal oxide can be selected from one or more of oxides of Ni, Co, Cr, and Al.

[0028] In an optional embodiment, the positive electrode sheet comprises a positive electrode material, and the positive electrode material comprises a ternary material.

[0029] Preferably, the specific surface area of the ternary material is z m 2 / g, and z satisfies: 0.4≤z≤2, preferably, 0.4≤z≤1.35.

[0030] In an optional embodiment, the electrolyte further comprises a phosphorus-containing additive, and the addition amount of the phosphorus-containing additive is f% of the mass of the electrolyte, and f satisfies: 0.1≤f≤5.

[0031] Further, the phosphorus-containing additive comprises one or more of lithium difluorophosphate, tris(2,2,2-trifluoroethyl) phosphate, triphenyl phosphate, ethoxy pentafluoro-cyclotriphosphazene, triphenyl phosphine oxide, triphenyl phosphine, p-toluoyl phosphate, and cresyl diphenyl phosphate.

[0032] In an optional embodiment, the electrolyte further comprises a sulfur-containing additive, and the addition amount of the sulfur-containing additive is e% of the mass of the electrolyte, and e satisfies: 0.1≤e≤3.

[0033] Further, the sulfur-containing additive comprises one or more of vinyl sulfate, 1,3-propane sultone, 1-propene-1,3-sultone, 5-methylthiacyclopentane 2,2-dioxide, 1,3-propane sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-butane sultone, and fluorinated 1,3-propane sultone.

[0034] The technical scheme has the following advantages:

[0035] The lithium metal battery provided by the application comprises a negative electrode sheet with increased active layer thickness, a current collector with a protective layer, and an electrolyte containing organic solvent A and compound C. The protective layer in the application has the effect of increasing the tensile strength of the foil, which can better avoid the problem of foil rupture caused by the increase of internal stress due to the expansion of the active layer, and inhibit the expansion of the negative electrode active layer and improve the thermal safety performance of the battery. The organic solvent A used in the application can effectively accelerate the transmission of ions, reduce the risk of thermal runaway, reduce polarization, reduce the expansion of the negative electrode sheet, and improve the safety performance of the battery. Compound C in the application can effectively reduce the flammability of organic solvent A itself and reduce the viscosity of the electrolyte, effectively improving the safety performance of the battery. The organic solvent A, the protective layer and compound C in the application can effectively improve the thermal runaway problem of the battery and improve the cycle rate performance of the battery.

[0036] Additional layers and advantages of the embodiments of the application will be described and shown in part in the following description, or will be apparent from the embodiments of the application. DETAILED DESCRIPTION

[0037] The following examples are provided to better further understand the application and are not limited to the best mode, and do not limit the content and protection scope of the application. Any person under the inspiration of the application or the combination of the application with other prior art features will fall within the protection scope of the application.

[0038] The specific experimental steps or conditions not mentioned in the examples can be carried out according to the conventional experimental steps described in the literature in the art or the operation or conditions. The reagents or instruments not mentioned by the manufacturer are conventional reagent products that can be obtained by market purchase.

[0039] In addition, the technical features involved in different embodiments of the application described below can be combined with each other as long as there is no conflict between them.

[0040] The application provides a lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte;

[0041] The negative electrode sheet comprises a current collector and an active layer arranged on at least one side surface of the current collector, and the current collector comprises a foil and a protective layer arranged on at least one side surface of the foil;

[0042] The thickness of the active layer in the negative electrode sheet is d μm, and d satisfies: 30≤d≤100, wherein the thickness d of the active layer refers to the thickness of the active layer on one side of the current collector;

[0043] The electrolyte comprises organic solvent A and compound C, and the mass fraction of the organic solvent A in the electrolyte is a%, and a satisfies: 30≤a≤80;

[0044] The organic solvent A includes at least one of the structures shown in formula 1,

[0045] Formula 1: Wherein, R1, R2, R3 are independently selected from H, halogen, halogen-substituted or unsubstituted hydrocarbon group with carbon number of 1-8, hydroxyl group, R2 and R3 can also be connected to form a ring.

[0046] The compound C includes at least one of the structures shown in formula 2,

[0047] Formula 2: Wherein, R4, R5 are independently selected from H, F-substituted or unsubstituted hydrocarbon group with carbon number of 1-10, hydroxyl group.

[0048] The protective layer itself has a certain effect of increasing the tensile strength of the foil, which can better avoid the problem of foil rupture caused by the increase of internal stress due to the swelling of the thick active layer, and to a certain extent, the swelling of the negative active layer is also alleviated; and the organic solvent A has high chemical stability, and has lower viscosity than traditional carbonate solvents, which can be as low as <20 mPa.s. Low viscosity can effectively ensure good wettability between the organic solvent A and the pole piece, better penetrate into the interior of the thick lithium metal negative pole piece, accelerate ion transport and desorption, thereby improving the utilization rate of active material, preventing the lithium metal negative active layer from having too large a difference in lithium ion concentration between the surface layer and the inner layer, reducing the polarization of the pole piece, inhibiting the swelling of the negative pole piece, reducing side reactions, reducing heat generation and accumulation, and avoiding the thermal runaway problem of lithium metal batteries; at the same time, low viscosity helps to quickly conduct heat and reduce safety hazards caused by heat concentration. The organic solvent A itself is flammable, so the battery in the present application still has the risk of thermal runaway. In order to solve the above problems, the present application adds the compound C to the organic solvent A. The compound C itself is not flammable, which can improve the flammability of the electrolyte containing the organic solvent A, and the compound C has very low viscosity. Therefore, when the compound C is added to the electrolyte, it not only improves the flammability of the electrolyte containing the organic solvent A, but also further reduces the viscosity of the electrolyte, and improves the thermal safety performance of the battery. Therefore, the organic solvent A, the protective layer and the compound C can effectively improve the thermal runaway problem of the battery and improve the cycle rate performance of the battery.

[0049] As an example, the mass percentage a% of the organic solvent A in the electrolyte can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or within a range between any two of the above values; the thickness d of the active layer of the negative electrode sheet can be 30, 40, 50, 60, 70, 80, 90, 100, or within a range between any two of the above values.

[0050] In an alternative embodiment, the organic solvent A comprises at least one of the following formulae 1-1 to 1-8:

[0051]

[0052]

[0053] and / or, the compound C comprises at least one of the following formulae 2-1 to 2-8:

[0054]

[0055] In an alternative embodiment, the mass percentage of the compound C in the electrolyte is c%, c satisfies: 0 < c < 50, the compound C is completely insoluble in the lithium salt B and does not participate in the electrochemical reaction, and does not affect the electrical performance; therefore, the addition of the compound C in the electrolyte can improve the fast charging and high performance of the battery without other side reactions.

[0056] As an example, the mass percentage c% of the compound C in the electrolyte can be 1%, 3%, 5%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or within a range between any two of the above values.

[0057] The electrolyte further comprises a lithium salt B, when the organic solvent A is used as the main solvent of the electrolyte, the organic solvent A has good solubility to the lithium salt, and can dissolve the higher content of the lithium salt according to the present application. In an alternative embodiment, the mass percentage of the lithium salt B in the electrolyte is b%, b satisfies: 10 < b < 40; preferably, 20 < b < 40; under this condition, the content of the movable lithium ions in the unit volume is high, which can improve the ionic conductivity in the negative electrode sheet, and effectively improve the fast charging and high performance of the battery.

[0058] As an example, the mass percentage b% of the lithium salt B in the electrolyte can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, or within a range between any two of the above values.

[0059] In an alternative embodiment, the lithium salt B comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethylsulfonylimide, lithium difluorobis(oxalato)phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, and lithium bis(trifluoromethylsulfonyl)imide.

[0060] In an alternative embodiment, by comprehensively regulating the mass percentage a% of the organic solvent A in the electrolyte, the mass percentage b% of the lithium salt B in the electrolyte, and the thickness d μm of the active layer of the negative electrode sheet, and by controlling a, b, and d within the range of a certain relationship, i.e., controlling 0.4 < d / (a+b) < 1.7, the cycle performance and safety of the battery can be effectively balanced; more preferably, within the range of 0.4 < d / (a+b) < 0.7, better cycle performance and safety performance can be effectively achieved.

[0061] For example, d / (a+b) can be 0.4, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, or within the range between any two of the above values.

[0062] In an alternative embodiment, when the negative electrode material has a large surface capacity, the battery can have a larger energy density, which can meet the use requirements of people for high energy density and large discharge current; however, a too large surface capacity also means that the negative electrode has a larger volume expansion and more serious lithium dendrite growth during charging and discharging. Therefore, in the present application, the surface capacity of the negative electrode sheet is x mAh / cm 2 , and x satisfies 5 ≤ x ≤ 12.

[0063] For example, the surface capacity x mAh / cm 2 of the negative electrode sheet can be 5 mAh / cm 2 , 6 mAh / cm 2 , 7 mAh / cm 2 , 8 mAh / cm 2 , 9 mAh / cm 2 , 10 mAh / cm 2 , 11 mAh / cm 2 , 12 mAh / cm 2 , or within the range between any two of the above values.

[0064] In the present application, when the negative electrode material has a larger surface capacity, it also means that the volume expansion of the negative electrode body is larger and the lithium dendrite growth is more serious during the charging and discharging process. The current collector with larger tensile strength than the ordinary current collector is used to avoid the fracture caused by excessive stress. At the same time, the protective film with a specific thickness on the surface of the current collector provides stress buffering during the lithium metal deposition and stripping process based on its certain buffering effect, and cooperates with the current collector to reduce the cracks and fractures caused by volume change.

[0065] In an alternative embodiment, the tensile strength of the current collector is σ MPa. When the current collector has larger tensile strength than the ordinary current collector, it can avoid the fracture caused by excessive stress. However, in order to obtain larger tensile strength, the thickness of the current collector needs to be thicker, which is not conducive to maintaining high energy density. In the present application, the tensile strength of the current collector is preferably σ, which satisfies: 350≤σ≤800.

[0066] For example, the tensile strength of the current collector σ MPa can be 350 MPa, 400 MPa, 450 MPa, 500 MPa, 550 MPa, 600 MPa, 650 MPa, 700 MPa, 750 MPa, 800 MPa, or within a range consisting of any two of the above values.

[0067] In an alternative embodiment, the thickness of the protective layer is y nm. The protective film on the surface of the foil (current collector) has a certain buffering effect, which provides stress buffering during the lithium metal deposition and stripping process, and reduces the cracks and fractures caused by volume change. However, when the protective thickness is too large, it will lead to a decrease in the energy density per unit volume of the battery. Therefore, in the present application, preferably, y satisfies: 0

[0068] For example, the thickness of the protective layer y nm can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or within a range consisting of any two of the above values.

[0069] In an alternative embodiment, by comprehensively controlling the product value of the mass percentage a% of the organic solvent A in the electrolyte and the thickness y nm of the protective layer, the battery energy density can be improved and relatively high cycle performance can be effectively obtained while ensuring safety performance. Specifically, when the a% content is low, the thickness of the protective layer needs to be increased to ensure safety performance; when the a% content is high, the negative electrode expansion is relatively reduced, the internal stress is reduced, the electrolyte viscosity is reduced, the wettability of the negative electrode is improved, the thickness of the protective layer can be reduced to reduce the battery volume, thereby improving the energy density per unit volume of the battery and improving the cycle performance, therefore, ay≥180, preferably, 650≥ay≥180, more preferably, 380≥ay≥280.

[0070] As understood by those skilled in the art, the surface capacity in the present application refers to the number of lithium ions or electric quantity that can be accommodated per square centimeter of negative electrode area. The surface capacity is calculated as follows: surface capacity = electric capacity (mAh) / negative electrode sheet area, and the electric capacity is obtained by testing the charging capacity of the assembled battery.

[0071] The tensile strength is detected as follows: the current collector is cut into a small strip of 15 mm±0.2 mm, a WD-D3 electronic universal testing machine is used, the gap between the upper and lower clamps is 50 mm, the current collector is clamped at both ends of the clamps, a speed of 100 mm / min is used to start the test, until the equipment stops testing, and the breaking strength (tensile strength) σ is recorded; the error of 3 tests is not more than 10%, and the average value is taken;

[0072] Alternatively, the negative electrode sheet is cut into a small strip of 15 mm±0.2 mm, then the surface active material is gently wiped off using alcohol, and after natural air drying, the WD-D3 electronic universal testing machine is used to detect by the above detection method.

[0073] In an alternative embodiment, the foil is a copper foil;

[0074] And / or, the material of the protective layer is at least one of an ion conductor, a conductive polymer, and a metal oxide; preferably, the material of the protective layer includes at least one of Cr2O3, Al2O3, Co3O4, NiO, graphite, polyimide, polyaniline, polyacrylamide, and polypyrrole.

[0075] In an alternative embodiment, the positive electrode material in the positive electrode sheet is an NCM ternary material;

[0076] Preferably, the specific surface area of the NCM ternary material is z m 2 / g, z satisfies: 0.4≤z≤2, preferably, 0.4≤z≤1.35.

[0077] The greater the specific surface area of the NCM ternary positive electrode material, the more surface active sites it has, which helps to improve the wettability of the electrolyte on the surface of the positive electrode material, thereby promoting the penetration of the electrolyte and the transmission of lithium ions, and thus better matching the thicker negative electrode material described in the application, so that the battery has better fast charging performance. However, if the specific surface area is too large, the ion transmission rate may be limited, causing changes in electrode potential, affecting the performance of the battery, at the same time, the mechanical strength is low, and it is easy to break or deform when subjected to external force, and the surface may change during the cycle process, affecting the cycle stability, the specific surface area z of the NCM ternary material in the application is set to 0.4-2, preferably 0.4-1.35.

[0078] For example, the specific surface area z of the NCM ternary material m 2 / g can be 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 2.0m 2 / g or within a range consisting of any two of the above values.

[0079] In an alternative embodiment, the electrolyte further comprises a phosphorus-containing additive, and the amount of the phosphorus-containing additive added is f% of the mass of the electrolyte, f satisfies: 0≤f≤5.

[0080] Since the melting point of the compound A described in the application is higher than that of ordinary carbonate solvents, there may be a change in state at low temperatures, forming a solid, causing lithium to precipitate, and thus affecting the low-temperature cycle performance; in addition, the negative electrode sheet described in the application is thicker than ordinary lithium metal batteries, so the low-temperature cycle problem of the lithium metal battery described in the application is more pronounced at low temperatures. The phosphorus-containing additive described in the application not only forms a stable CEI film on the surface of the positive electrode, protecting the structure of the positive electrode material, but also participates in the solvation structure of the decomposition product, reducing the migration resistance of lithium ions in the electrolyte and improving its electrical conductivity.

[0081] For example, the phosphorus-containing additive can be added in an amount of 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or within a range defined by any two of the above values.

[0082] Preferably, the phosphorus-containing additive includes one or more of lithium difluorophosphate, tris(2,2,2-trifluoroethyl) phosphate, triphenyl phosphate, ethoxy pentafluoro cyclo-triphosphazene, triphenyl phosphine oxide, triphenyl phosphine, p-toluoyl phosphate, and cresyl diphenyl phosphate.

[0083] In an alternative embodiment, the electrolyte further includes a sulfur-containing additive, and the sulfur-containing additive is added in an amount of e% of the mass of the electrolyte, e satisfying 0≤e≤3.

[0084] In the present application, a sulfur compound can also be included in the electrolyte. The sulfur compound can form a low-impedance SEI film on the surface of the negative electrode, reduce the interface impedance, improve the contact and electron transport performance of the electrode / electrolyte interface, reduce the polarization, improve the power performance of the battery, and reduce the risk of thermal runaway.

[0085] For example, the sulfur-containing additive can be added in an amount of 0.1%, 0.3%, 0.5%, 0.7%, 0.9%, 1.5%, 2%, 2.5%, 3%, or within a range defined by any two of the above values.

[0086] Preferably, the sulfur-containing additive includes one or more of vinyl sulfates, 1,3-propane sultone, 1-propene-1,3-sultone, 5-methylthiophene 2,2-dioxide, 1,3-propene sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-butane sultone, and fluorinated 1,3-propane sultone.

[0087] More preferably, 0

[0088] The positive electrode sheet of the present application includes a current collector and a positive electrode active material layer disposed on the surface of the current collector. The positive electrode active material layer includes 80% to 99.8% of a ternary material, 0.1% to 10% of a conductive agent, and 0.1% to 10% of a binder. Preferably, the positive electrode active material layer includes 90% to 99.6% of a high-nickel ternary material, 0.2% to 5% of a conductive agent, and 0.2% to 5% of a binder.

[0089] The conductive agent in the positive electrode sheet is not particularly limited, and can be selected from the conductive agents conventionally used in the art, including but not limited to one or more of acetylene black, conductive carbon black, ketjen black, conductive graphite, carbon nanotube, conductive carbon fiber, graphene.

[0090] The binder in the positive electrode sheet is not particularly limited, and can be selected from the binders conventionally used in the art, including but not limited to one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium carboxymethyl cellulose, butadiene-styrene rubber, polyethylene oxide.

[0091] The negative electrode sheet comprises a current collector and an active layer disposed on at least one side surface of the current collector, the active layer comprising a negative electrode active material, which can be any negative electrode active material known in the art for use in lithium metal batteries. The negative electrode active material can be at least one of lithium metal and lithium alloy. The current collector of the negative electrode sheet comprises a foil and a protective layer disposed on at least one side surface of the foil, which can be a high-strength copper foil known in the art. The active layer further comprises a conductive agent and a binder, and the types of the conductive agent and the binder in the negative electrode sheet are not particularly limited, and can be selected from the same range as the conductive agent and the binder in the positive electrode sheet, which will not be described here.

[0092] The material and shape of the separator used in the lithium metal battery of the present application are not particularly limited, and can include any technology disclosed in the prior art.

[0093] The present application will be further described in detail below in conjunction with specific examples, which should not be construed as limiting the scope of the present application. In all examples and comparative examples of the present application, the unit wt% represents the mass percentage.

[0094] Example 1

[0095] A lithium metal battery was prepared as follows:

[0096] (1) Preparation of positive electrode sheet

[0097] An active positive material (NCM811) with a specific surface area z of 1 m 2 / g, polyvinylidene fluoride, conductive carbon black and carbon nanotube were mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) was added, and stirring was carried out under the action of a vacuum stirrer until the mixed system became a homogeneous positive active slurry; the positive active slurry was uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil was dried, rolled, and cut to obtain the desired positive electrode sheet, wherein the areal density of the positive electrode sheet was 3.5 mAh / cm 2 .

[0098] (2) Preparation of negative electrode sheet

[0099] Lithium metal is compounded onto a copper foil with a surface protective layer y of 5 nm and a tensile strength s of 500 MPa by a physical rolling method, the material of the protective layer is Cr2O3, the pressure of the roller is adjusted to make the copper foil double-sided coated with lithium alloy, the thickness of the active layer in the negative electrode sheet is d pm, after cutting and slitting, a negative electrode sheet is obtained, which is placed in a dry argon glove box for storage, the surface capacity x of the negative electrode sheet is 7 mAh / cm 2 .

[0100] (3) Preparation of electrolyte

[0101] In an argon-filled glove box (H2O<0.1 ppm, O2<0.1 ppm), a compound A based on a% of the total mass of the electrolyte is added to a lithium salt based on b% of the total mass of the electrolyte, dissolved and stirred uniformly, a compound C based on c% of the total weight of the electrolyte is added, and 1.5% of lithium difluorophosphate and 1% of ethylene sulfate based on the total mass of the electrolyte is added, and the electrolyte is obtained after stirring uniformly, the specific amount is shown in Table 1.

[0102] (4) Preparation of battery

[0103] The positive electrode sheet prepared in step (1) and the negative electrode sheet prepared in step (2) and the separator are stacked in the order of positive electrode sheet, separator, negative electrode sheet and separator to obtain an electric core; the electric core is placed in an outer packaging aluminum foil, and the electrolyte prepared in step (3) is injected into the outer packaging aluminum foil, and after vacuum packaging, standing, formation, shaping, sorting and other processes, a lithium metal battery is obtained.

[0104] Table 1

[0105]

[0106]

[0107] The battery of the application has a charge-discharge range of 3.0-4.25V.

[0108] Comparative Example 1

[0109] A lithium metal battery, which is different from Example 1-1 in that the thickness d of the negative electrode sheet active layer is adjusted to 120 pm, and other parameters not shown are the same as Example 1-1.

[0110] Comparative Example 2

[0111] A lithium metal battery, which is different from Example 1-1 in that the content of compound C is 0%, and the content of compound A is adjusted to 76.5% at the same time, and other parameters not shown are the same as Example 1-1.

[0112] Comparative Example 3

[0113] A lithium metal battery, which is different from Example 1-1 in that the foil surface has no protective layer, i.e. the thickness of the protective layer is 0 nm, and other parameter conditions not shown are exactly the same as Example 1-1.

[0114] Comparative Example 4

[0115] A lithium metal battery, which is different from Example 1-1 in that ethylene carbonate (EC) is used instead of compound A, the content of EC is 65%, and other parameter conditions not shown are exactly the same as Example 1-1.

[0116] Example 2

[0117] A lithium metal battery, which is different from Example 1-1 in that the parameter specifications of the negative electrode sheet and the positive electrode sheet are different, and the specific settings are shown in Table 2 as follows:

[0118] Table 2

[0119]

[0120]

[0121] Other parameter conditions not shown are exactly the same as Example 1-1.

[0122] Example 3

[0123] A lithium metal battery, which is different from Example 1-1 in that the amount and type of sulfur-containing additives and phosphorus-containing additives are different, and the content of compound A is adjusted, and the specific settings are shown in Table 3 as follows:

[0124] Table 3

[0125] a b c e f d Sulfur-containing additive Phosphorus-containing additive Example 3-1 66 21 11.5 0 1.5 55 Vinyl sulfate Lithium difluorophosphate Example 3-2 66 21 11.5 0.1 1.4 55 Vinyl sulfate Lithium difluorophosphate Example 3-3 63 21 11.5 3 1.5 55 Vinyl sulfate Lithium difluorophosphate Example 3-4 61 21 11.5 5 1.5 55 Vinyl sulfate Lithium difluorophosphate Example 3-5 65 21 11.5 1 1.5 55 1,3-Propenesulfonic acid lactone Lithium difluorophosphate Example 3-6 65 21 11.5 1 1.5 55 5-Methylthiopentyl 2,2-dioxide Lithium difluorophosphate Example 3-7 66.5 21 11.5 1 0 55 Vinyl sulfate Lithium difluorophosphate Example 3-8 66.5 21 11.5 0.9 0.1 55 Vinyl sulfate Lithium difluorophosphate Example 3-9 63.5 21 11.5 1 3 55 Vinyl sulfate Lithium difluorophosphate Example 3-10 61.5 21 11.5 1 5 55 Vinyl sulfate Lithium difluorophosphate Example 3-11 60.5 21 11.5 1 6 55 Vinyl sulfate Lithium difluorophosphate Example 3-12 65 21 11.5 1 1.5 55 Vinyl sulfate Triphenyl phosphate Example 3-13 65 21 11.5 1 1.5 55 Vinyl sulfate Ethoxy pentafluorocyclotriphosphazene

[0126] Other parameter conditions not shown are exactly the same as Example 1-1.

[0127] Experimental Example

[0128] The lithium ion batteries obtained in the examples and comparative examples were respectively subjected to cycle performance test and short circuit safety test.

[0129] 1. 0℃ 0.2C / 1C cycle performance test

[0130] The batteries obtained from the examples and comparative examples were discharged at 0°C to 3.0V at a current of 1C, then charged at a constant current of 0.2C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, rested for 5 min, then discharged at a constant current of 1C to a voltage of 3.0V, which was one charge-discharge cycle. The thickness of the battery was recorded, the discharge capacity of the first week was x mAh, and the discharge capacity of the Nth week was y mAh; the capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate R = y / x of the Nth week, and the cycle number when the battery capacity retention rate was 80% was recorded.

[0131] 2, 25°C 0.2C / 1C cycle performance test

[0132] The batteries obtained from the examples and comparative examples were discharged at 25°C to 3.0V at a current of 1C, then charged at a constant current of 0.2C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, rested for 5 min, then discharged at a constant current of 1C to a voltage of 3.0V, which was one charge-discharge cycle. The thickness of the battery was recorded, the discharge capacity of the first week was x mAh, and the discharge capacity of the Nth week was y mAh; the capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate R = y / x of the Nth week, and the cycle number when the battery capacity retention rate was 80% was recorded.

[0133] 3, 25°C 0.5C / 3C cycle test

[0134] The batteries obtained from the examples and comparative examples were discharged at 25°C to 3.0V at a current of 3C. Then charged at a constant current of 0.5C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, rested for 5 min, then discharged at a constant current of 3C to a voltage of 3.0V, which was one charge-discharge cycle. The discharge capacity of the first week was x mAh, and the discharge capacity of the Nth week was y mAh; the capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate R = y / x of the Nth week, and the cycle number when the battery capacity retention rate was 80% was recorded.

[0135] 4, Battery short circuit safety test

[0136] The batteries obtained from the examples and comparative examples were discharged at 25°C to 3.0V at a current of 5C. Then charged at a constant current of 1C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, rested for 5 min, then discharged at a constant current of 5C to a voltage of 3.0V, which was one charge-discharge cycle. If the voltage value suddenly dropped during the cycle, especially from the normal value to near zero level, it indicated that a short circuit occurred inside the battery, and whether the battery had thermal runaway, fire or explosion when the battery short-circuited was recorded.

[0137] The above detection results of the examples and comparative examples of the present application are shown in Tables 4-6.

[0138] Table 4

[0139]

[0140]

[0141] Table 5

[0142]

[0143] Table 6

[0144]

[0145] Obviously, the above examples are merely illustrative and not intended to limit the embodiments. Based on the above description, other different forms of changes or variations can be made by those of ordinary skill in the art. Here, it is not necessary and impossible to exhaust all the embodiments. The obvious changes or variations derived therefrom are still within the scope of protection created by the present application.

Claims

1. A lithium metal battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, characterized in that, the negative electrode sheet comprises a current collector and an active layer arranged on at least one side surface of the current collector, the current collector comprises a foil and a protective layer arranged on at least one side surface of the foil; the thickness of the active layer is d μm, and d satisfies: 30≤d≤100; the electrolyte comprises an organic solvent A and a compound C, the mass percentage of the organic solvent A in the electrolyte is a%, and a satisfies: 30≤a≤80; the mass percentage of the compound C in the electrolyte is c%, and c satisfies: 0<c≤50; the organic solvent A comprises at least one of the structures shown in formula 1, Formula 1: wherein R1, R2, R3 are independently selected from H, halogen, halogen substituted or unsubstituted hydrocarbyl group having 1 to 8 carbon atoms, hydrocarbyloxy group, and R2, R3 can also be linked to form a ring; the compound C comprises at least one of the structures shown in formula 2, Formula 2: wherein R4is selected from H, F-substituted or unsubstituted hydrocarbyl of 1-10 carbon atoms, hydrocarboxy, and R5is selected from F-substituted or unsubstituted hydrocarbyl of 1-10 carbon atoms, hydrocarboxy.

2. The lithium metal battery of claim 1, wherein, the organic solvent A comprises at least one of the following formula 1-1 to formula 1-8: and / or, the compound C comprises at least one of the following formula 2-1 to formula 2-8: 。 3. The lithium metal battery of claim 1, wherein, the electrolyte further comprises a lithium salt B, the lithium salt B comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium bisfluorosulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide and lithium bis(trifluoromethylsulfonyl)imide.

4. The lithium metal battery of claim 3, wherein, The mass percentage of the lithium salt B in the electrolyte is b%, and b satisfies: 10≤b≤40.

5. The lithium metal battery of claim 4, wherein, The lithium metal battery satisfies: 0.4<d / (a+b)<1.

7.

6. The lithium metal battery of claim 5, wherein, 0.4<d / (a+b)<0.

7.

7. The lithium metal battery of any one of claims 1-6, wherein, The surface capacity of the negative electrode sheet is xm Ah / cm2 2 x satisfies: 5≤x≤12; and / or, the tensile strength of the current collector is σ MPa, and σ satisfies: 350≤σ≤800; and / or, the thickness of the protective layer is y nm, and y satisfies: 0<y≤10; ay≥180.

8. The lithium metal battery of claim 7, wherein, 650≥ay≥180.

9. The lithium metal battery of claim 8, wherein, 380≥ay≥280.

10. The lithium metal battery of any one of claims 1-6, wherein, The foil is a copper foil; and / or, the material of the protective layer comprises at least one of a metal oxide, a carbon-based material and a conductive polymer.

11. The lithium metal battery of claim 10, wherein, The material of the protective layer comprises at least one of Cr2O3, Al2O3, Co3O4, NiO, graphite, polyimide, polyaniline, polyacrylamide and polypyrrole.

12. The lithium metal battery of any one of claims 1-6, wherein, The positive electrode sheet comprises a positive electrode material, and the positive electrode material comprises a ternary material.

13. The lithium metal battery of claim 12, wherein, The specific surface area of the ternary material is z m 2 / g, and z satisfies: 0.4≤z≤2.

14. The lithium metal battery of claim 13, wherein, 0.4≤z≤1.35。 15. The lithium metal battery of any one of claims 1-6, wherein, The electrolyte further comprises a phosphorus-containing additive and / or a sulfur-containing additive.

16. The lithium metal battery of claim 15, wherein, The addition amount of the phosphorus-containing additive is f% of the mass of the electrolyte, and f satisfies: 0.1≤f≤5; and / or, the addition amount of the sulfur-containing additive is e% of the mass of the electrolyte, and e satisfies: 0.1≤e≤3.

17. The lithium metal battery of claim 15, wherein, The phosphorus-containing additive comprises one or more of lithium difluorophosphate, tris(2,2,2-trifluoroethyl) phosphate, triphenyl phosphate, ethoxy pentafluoro cyclo triphosphazene, triphenyl phosphine oxide, triphenyl phosphine, p-toluoyl phosphate and toluene diphenyl phosphate; and / or, the sulfur-containing additive comprises one or more of vinyl sulfate, 1,3-propane sulfone lactone, 5-methyl oxathiane 2,2-dioxide, 1,3-propylene sulfone lactone, 2,4-butane sulfone lactone, 1,4-butane sulfone lactone, 1,3-butane sulfone lactone and fluorinated 1,3-propane sulfone lactone.

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