Electrolyte for lithium metal battery, lithium metal battery and electric device

Abstract

The invention relates to an electrolyte for a lithium metal battery, the lithium metal battery and a power utilization device, the electrolyte for the lithium metal battery comprises a first electrolyte and a second electrolyte, the first electrolyte comprises a first solvent, the first solvent comprises at least one of a sulfone solvent and a dinitrile solvent, and the second electrolyte comprises a chain monoether solvent, the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent is greater than or equal to 25.

Description

Technical Field

[0001] The present application relates to an electrolyte for a lithium metal battery, a lithium metal battery, and an electrical device using the same. Background Art

[0002] Batteries have the advantages of reliable working performance, no pollution, no memory effect, etc., and are thus widely used. For example, with the increasing attention to environmental protection issues, new energy vehicles are becoming increasingly popular, and the demand for power lithium metal batteries will show an explosive growth.

[0003] As the application range of batteries becomes wider and wider, the requirements for battery performance are gradually becoming more stringent, but the lithium metal battery has poor cycling performance. Summary of the Invention

[0004] The present application provides an electrolyte for a lithium metal battery, a lithium metal battery, and an electrical device using the same, which can improve the cycling performance when the electrolyte for a lithium metal battery is applied to a lithium metal battery.

[0005] In a first aspect, the present application provides an electrolyte for a lithium metal battery, which includes a first electrolyte and a second electrolyte. The first electrolyte includes a first solvent, and the first solvent includes at least one of a sulfone solvent and a dinitrile solvent. The second electrolyte includes a chain monoether solvent, and the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent is ≥25.

[0006] Thus, in the embodiments of the present application, due to the polarity difference of the respective solvents of the first electrolyte and the second electrolyte, a two-phase electrolyte system is formed by intrinsic phase separation, and there is a clear liquid-liquid interface between the first electrolyte and the second electrolyte. The first electrolyte is used to contact the positive electrode plate. Since the sulfone solvent and / or the dinitrile solvent has excellent electrochemical oxidation stability and is not easily decomposed, the interfacial stability between it and the positive electrode plate can be improved; the second electrolyte is used to contact the negative electrode plate. Since the chain monoether solvent has excellent reduction stability and is not easily decomposed, the interfacial stability between it and the negative electrode plate can be improved, thereby being able to broaden the actual electrochemical window of the electrolyte and being beneficial to improving the cycling stability of the lithium metal battery.

[0007] In some embodiments, the relative dielectric constant of the sulfone solvent is 25 to 60; it can be optionally 28 to 50; optionally, the sulfone solvent includes at least one of a C4 to C6 cyclic sulfone and a C2 to C8 chain sulfone; further optionally, the C4 to C6 cyclic sulfone includes at least one of sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane; further optionally, the C2 to C8 chain sulfone includes at least one of dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl isopropyl sulfone, dipropyl sulfone, dibutyl sulfone.

[0008] Therefore, in the embodiments of the present application, the sulfone solvent has strong molecular polarity and excellent electrochemical oxidation stability, and the interfacial stability between the sulfone solvent and the positive electrode can be significantly improved, which is beneficial to enhancing the structural stability of the positive active material, and further improving the cycle stability of the lithium metal battery.

[0009] In some embodiments, the relative dielectric constant of the dinitrile solvent is 50 to 80; it can be selected as 50 to 60; optionally, the dinitrile solvent includes at least one of C3 to C6 linear dinitriles; further optionally, the C3 to C6 linear dinitriles include at least one of malononitrile, succinonitrile, glutaronitrile, and adiponitrile.

[0010] Therefore, in the embodiments of the present application, the dinitrile solvent has strong molecular polarity and excellent electrochemical oxidation stability, and the interfacial stability between the dinitrile solvent and the positive electrode can be significantly improved, which is beneficial to enhancing the structural stability of the positive active material, and further improving the cycle stability of the lithium metal battery.

[0011] In some embodiments, the relative dielectric constant of the linear monoether solvent is 2.0 to 6.0; it can be selected as 2.0 to 4.5; optionally, the linear monoether solvent includes C2 to C10 linear monoether solvents; it can be selected as C4 to C8 linear monoether solvents; further optionally, the C2 to C10 linear monoether solvents include at least one of diethyl ether, dipropyl ether, dibutyl ether, methyl propyl ether, and methyl butyl ether; further optionally, the C2 to C10 linear monoether solvents include at least one of dipropyl ether, dibutyl ether, and methyl butyl ether.

[0012] Therefore, in the embodiments of the present application, the linear monoether solvent has weak molecular polarity and excellent electrochemical reduction stability, and the interfacial stability between the linear monoether solvent and the negative electrode can be significantly improved, thereby improving the cycle stability of the lithium metal battery.

[0013] In some embodiments, the total volume of the first solvent in the first electrolyte is A mL, and the volume of the linear monoether solvent in the second electrolyte is B mL, where A / B is 0.5 to 2; it can be selected as 0.8 to 1.2. By regulating the volume ratio of the first solvent and the second solvent, the chemical potential balance of lithium ions can be quickly achieved during the migration process in the two-phase system, the migration barrier of lithium ions can be reduced, the ionic conductivity of the electrolyte can be improved, and the kinetic performance of the battery can be improved.

[0014] In some embodiments, the first electrolyte further includes a first additive, and the first additive includes at least one of lithium nitrate, lithium difluorophosphate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; optionally, based on the total mass of the first solvent, the mass content of the first additive is 0.5% to 10%; it can be selected as 0.5% to 2.5%.

[0015] Therefore, in the embodiments of the present application, the first additive can form a Cathode Electrolyte Interphase (CEI) film on the surface of the positive electrode plate, which can play a good protective role for the positive active material in the positive electrode plate, improve the structural stability of the positive active material, and thus improve the cycle performance of the lithium metal battery; moreover, the above-mentioned first additive can also reduce the viscosity of the electrolyte and further improve the ionic conductivity of the first electrolyte, which is beneficial to further improving the kinetic performance of the lithium metal battery.

[0016] In some embodiments, the second electrolyte further includes a second additive, and the second additive may include at least one of lithium nitrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,3-dioxolane, dimethoxymethane, and dimethoxyethane; optionally, based on the total mass of the chain monoether solvent, the mass content of the second additive is 0.5% to 10%; preferably 3% to 10%.

[0017] Therefore, in the embodiments of the present application, the second additive can form a Solid Electrolyte Interphase (SEI) film on the surface of the negative electrode plate, which can play a good protective role for the negative active material in the negative electrode plate, improve the structural stability of the negative active material, and thus improve the cycle performance of the lithium metal battery; moreover, the above-mentioned second additive can also further improve the ionic conductivity of the second electrolyte, which is beneficial to further improving the kinetic performance of the lithium metal battery.

[0018] In some embodiments, the first electrolyte further includes a first lithium salt, and the first lithium salt includes at least one of lithium hexafluorophosphate (LiPF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), and lithium difluoro(oxalato)borate (LiDFOB); optionally, the first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF 6 ); further optionally, the concentration of the first lithium salt is 0.5 mol / L to 3.0 mol / L; preferably 0.5 mol / L to 2.0 mol / L.

[0019] Therefore, in the embodiments of the present application, the first lithium salt has strong lithium ion dissociation ability and excellent electrochemical stability in the first solvent.

[0020] In some embodiments, the second electrolyte further includes a second lithium salt, and the second lithium salt includes lithium hexafluorophosphate (LiPF 6)、at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and lithium difluoro(oxalato)borate (LiDFOB); optionally, the second lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI); further optionally, the concentration of the second lithium salt is from 0.5 mol / L to 3.0 mol / L; optionally from 0.5 mol / L to 1.2 mol / L.

[0021] Thus, in the embodiments of the present application, the second lithium salt has strong lithium ion dissociation ability and excellent electrochemical stability in the second solvent.

[0022] In a second aspect, the present application provides a lithium metal battery, comprising an electrolyte for a lithium metal battery according to any one of the embodiments of the first aspect of the present application.

[0023] In some embodiments, the lithium metal battery further includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material may include a lithium-containing transition metal oxide; optionally, the lithium-containing transition metal oxide includes at least one of compounds of the general formula Li a Ni b Co c M d O e A f , where 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes at least one of N, F, S, and Cl.

[0024] In a third aspect, the present application provides an electrical device, comprising a lithium metal battery according to any one of the embodiments of the second aspect of the present application, and the lithium metal battery is used to provide electrical energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 is a schematic diagram of an embodiment of the lithium metal battery of the present application.

[0027] Figure 2 is Figure 1Exploded schematic diagram of an embodiment of a lithium metal battery.

[0028] Figure 3 It is a schematic diagram of an embodiment of the battery module of the present application.

[0029] Figure 4 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0030] Figure 5 is Figure 4 Exploded schematic diagram of the embodiment of the battery pack shown.

[0031] Figure 6 It is a schematic diagram of an embodiment of an electrical device including the lithium metal battery of the present application as a power source.

[0032] The description of the reference numerals is as follows:

[0033] 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module;

[0034] 5. Lithium metal battery; 51. Housing; 52. Electrode assembly;

[0035] 53. Cover plate;

[0036] 6. Electrical device. Detailed implementation manners

[0037] Hereinafter, embodiments of the electrolyte for a lithium metal battery, the lithium metal battery, and the electrical device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0038] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. 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 include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise stated, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] If there is no special instruction, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0040] If there is no special instruction, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0041] If there is no special instruction, all steps S of this application can be carried out sequentially or randomly, preferably sequentially. For example, a method includes steps S(a) and (b), which means that the method can include steps S(a) and (b) carried out sequentially, or can also include steps S(b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step S(c), it means that step S(c) can be added to the method in any order. For example, the method can include steps S(a), (b), and (c), or can also include steps S(a), (c), and (b), or can also include steps S(c), (a), and (b), etc.

[0042] A lithium metal battery includes an electrode assembly and an electrolyte, a positive electrode plate, a negative electrode plate, and an electrolyte. The positive electrode plate includes a positive electrode film layer containing a positive electrode active material, and the positive electrode active material is a donor that provides active ions such as lithium ions for the lithium metal battery. The negative electrode plate includes a negative electrode film layer containing a negative electrode active material, and the negative electrode active material can act as an acceptor for lithium ions. The electrolyte provides a migration path for active ions between the positive electrode plate and the negative electrode plate.

[0043] Since the theoretical specific capacity of lithium metal is relatively high, and it has a relatively low density and a relatively negative electrode potential, using lithium metal as the negative active material can significantly increase the energy density of lithium metal batteries. In this case, lithium metal batteries can also be referred to as lithium metal batteries. To further increase the energy density of lithium metal batteries, high-voltage positive active materials are usually used for the positive active material. However, the interface between the high-voltage positive active material and the electrolyte is unstable, and the electrolyte is prone to oxidation and decomposition, increasing the irreversible capacity of lithium metal batteries, thereby reducing the cycle stability of lithium metal batteries. Moreover, since the negative electrode plate is deposited with lithium metal, its reaction activity is relatively high, and it is easy to undergo side reactions with the electrolyte and be reduced and decomposed. The products of the side reactions may accumulate to form an interfacial film, thereby affecting the ion transport and charge transfer at the interface between the negative electrode plate and the electrolyte, affecting the stability of the negative electrode plate, and deteriorating the cycle stability of lithium metal batteries.

[0044] In view of the above problems, the embodiments of the present application start from the design of the electrolyte. During the charge and discharge process of the lithium metal battery, active ions are embedded and extracted back and forth between the positive electrode plate and the negative electrode plate, and the electrolyte plays a role in conducting active ions between the positive electrode plate and the negative electrode plate. The electrolyte of the present application is a two-phase system, in which one phase has a strong interfacial stability with the positive electrode plate with a high working potential, and the other phase has a strong interfacial stability with the negative electrode plate with a low working potential, thereby being able to improve the cycle performance of the lithium metal battery. Next, the technical solutions of the embodiments of the present application will be described in detail.

[0045] Electrolyte for lithium metal battery

[0046] In a first aspect, embodiments of the present application provide an electrolyte for a lithium metal battery.

[0047] The electrolyte for a lithium metal battery includes a first electrolyte and a second electrolyte. The first electrolyte includes a first solvent, and the first solvent includes at least one of a sulfone solvent and a dinitrile solvent. The second electrolyte includes a chain monoether solvent, and the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent is ≥25.

[0048] The relative dielectric constant is correlated with the polarity of a substance, and the magnitude of the relative dielectric constant can be used to reflect the magnitude of the polarity of the substance. The relative dielectric constant of the first solvent is greater than that of the chain monoether solvent. When the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent is within the above range, the polarity difference between the first solvent and the chain monoether solvent is relatively large. Exemplarily, the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent can be greater than or equal to 25, greater than or equal to 30, greater than or equal to 40, or greater than or equal to 50. As the difference increases, the possibility of intrinsic phase separation between the two is higher; the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent can also be less than or equal to 80, less than or equal to 70, less than or equal to 60, or less than or equal to 50. For example, the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent can be 25 to 50.

[0049] Sulfone solvents and dinitrile solvents have strong molecular polarity as the first solvent, and chain monoether solvents have relatively weak molecular polarity as the second solvent. Both the first solvent and the second solvent are organic solvents. Due to their strong chemical polarity difference, the solubility of the first solvent in the second solvent is small, or rather, the solubility of the second solvent in the first solvent is small. The first solvent and the second solvent are prone to phase separation to form a two-phase system, where one phase is the first electrolyte mainly composed of the first solvent, and the other phase is the second electrolyte mainly composed of the second solvent.

[0050] In other words, due to the polarity difference of their respective solvents, the first electrolyte and the second electrolyte form a two-phase electrolyte system through intrinsic phase separation, and there is a clear liquid-liquid interface between the first electrolyte and the second electrolyte. The first electrolyte is used to contact the positive electrode plate. Since sulfone solvents and / or dinitrile solvents have excellent electrochemical oxidation stability and are not easily decomposed, the interfacial stability between them and the positive electrode plate can be improved; the second electrolyte is used to contact the negative electrode plate. Since chain monoether solvents have excellent reduction stability and are not easily decomposed, the interfacial stability between them and the negative electrode plate can be improved, thereby being able to broaden the actual electrochemical window of the electrolyte and being beneficial to improving the cycle stability of the lithium metal battery.

[0051] In the embodiments of the present application, the relative dielectric constant of a substance has the well-known meaning in the art, specifically referring to the relative dielectric constant relative to a vacuum, and it can be detected by commonly used methods and equipment in the art. For example,

[0052] Testing instruments and equipment: bridge, vernier caliper, high and low temperature chamber, muffle furnace, tablet press.

[0053] Required materials: samples, conductive silver paste, special glue.

[0054] For liquid substances: Place the sample in a sample cell and then put it into a high-low temperature chamber. Set the temperature range, and the high-low temperature chamber heats up from low temperature to high temperature. During the heating process, measure the capacitance C of the sample with a bridge at specific temperature points. According to the formula ∈ r = ∈ / ∈ 0 = Cd / ∈ 0 S, where ∈ is the absolute dielectric constant, ∈ 0 is the vacuum dielectric constant, S is the facing area of the capacitor plates, d is the distance between the capacitor plates, and C is the capacitance of the sample to be measured. Usually, each sample needs to make 3 or more wafers, and the average value is taken after excluding outliers during the test.

[0055] For solid substances: Add glue to the sample powder to granulate it, put the granulated powder into a tablet press to press tablets (wafers), then put the wafers into a muffle furnace and slowly heat up and keep warm to remove the binder. Take out the wafers after removing the binder, coat silver on the front side. Put them into the muffle furnace to burn the silver. After taking them out, coat silver and burn the silver on the reverse side. After burning the silver, put the wafers into a special fixture and put the fixture together into a high-low temperature chamber. Set the temperature range, and the high-low temperature chamber heats up from low temperature to high temperature. During the heating process, measure the capacitance C of the wafers with a bridge at specific temperature points. According to the formula ∈ r = ∈ / ∈ 0 = Cd / ∈ 0 S, where ∈ is the absolute dielectric constant, ∈ 0 is the vacuum dielectric constant, S is the facing area of the capacitor plates, d is the distance between the capacitor plates, and C is the capacitance of the sample to be measured. Usually, each powder needs to make 3 or more wafers, and the average value is taken after excluding outliers during the test.

[0056] In some embodiments, the total volume of the sulfone solvent and the dinitrile solvent in the first electrolyte is A mL, and the total volume of the chain monoether solvent in the second electrolyte is B mL, and A / B is from 0.5 to 2; it can be optionally from 0.8 to 1.2. By adjusting the volume ratio of the first solvent and the second solvent, it is possible to enable lithium ions to quickly reach the chemical potential equilibrium during the migration process in the two-phase system, reduce the migration barrier of lithium ions, increase the ionic conductivity of the electrolyte, and improve the kinetic performance of the battery.

[0057] Exemplarily, A / B can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 or a range composed of any two of the above values.

[0058] [First Electrolyte]

[0059] The first electrolyte includes a first solvent, and the first solvent includes at least one of a sulfone solvent and a dinitrile solvent; optionally, the first solvent is at least one of a sulfone solvent and a dinitrile solvent.

[0060] In some embodiments, the relative dielectric constant of the sulfone solvent is 25 to 60; it can be 28 to 50. The above sulfone solvent has strong molecular polarity and excellent electrochemical oxidation stability, and the interfacial stability with the positive electrode sheet can be significantly improved, which is beneficial to enhancing the structural stability of the positive active material, thereby further enhancing the cycle stability of the lithium metal battery.

[0061] Exemplarily, the relative dielectric constant of the sulfone solvent can be 25, 28, 30, 35, 40, 45, 50, 55, 60 or a range composed of any two of the above values.

[0062] In some embodiments, the sulfone solvent can include at least one of a C4 - C6 cyclic sulfone and a C2 - C8 linear sulfone. For example, the C4 - C6 cyclic sulfone can include at least one of a C4 cyclic sulfone, a C5 cyclic sulfone, and a C6 cyclic sulfone. For example, the C2 - C8 linear sulfone can include at least one of a C2 linear sulfone, a C3 linear sulfone, a C4 linear sulfone, a C5 linear sulfone, a C6 linear sulfone, a C7 linear sulfone, and a C8 linear sulfone.

[0063] Exemplarily, the C4 - C6 cyclic sulfone includes at least one of sulfolane, 3 - methylsulfolane, and 2,4 - dimethylsulfolane.

[0064] Exemplarily, the C2 - C8 linear sulfone includes at least one of dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl isopropyl sulfone, dipropyl sulfone, and dibutyl sulfone.

[0065] In some embodiments, the relative dielectric constant of the dinitrile solvent is 50 to 80; it can be 50 to 60. The above dinitrile solvent has strong molecular polarity and excellent electrochemical oxidation stability, and the interfacial stability with the positive electrode sheet can be significantly improved, which is beneficial to enhancing the structural stability of the positive active material, thereby further enhancing the cycle stability of the lithium metal battery.

[0066] Exemplarily, the relative dielectric constant of the dinitrile solvent can be 50, 55, 60, 65, 70, 75, 80 or a range composed of any two of the above values.

[0067] In some embodiments, the dinitrile solvent can include at least one of C3 - C6 linear dinitriles. For example, the C3 - C6 linear dinitriles can include at least one of a C3 linear dinitrile, a C4 linear dinitrile, a C5 linear dinitrile, and a C6 linear dinitrile. Of course, the dinitrile solvent can also be a cyclic nitrile solvent.

[0068] Exemplarily, the C3 to C6 chain dinitriles include at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile.

[0069] In some embodiments, the first electrolyte further includes a first lithium salt, and the first lithium salt includes at least one of lithium hexafluorophosphate (LiPF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium difluoro(oxalato)borate (LiDFOB). The above first lithium salt has strong lithium ion dissociation ability and excellent electrochemical stability in the first solvent.

[0070] Optionally, the first lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF 6 ).

[0071] In some embodiments, the concentration of the first lithium salt is 0.5 mol / L to 3.0 mol / L; optionally 0.5 mol / L to 2.0 mol / L. When the concentration of the first lithium salt is within the above range, it can improve the ionic conductivity of the first electrolyte and the wettability of the positive electrode sheet, which is beneficial to improving the migration rate of lithium ions, improving the kinetic performance of the lithium metal battery and reducing the polarization degree, thereby further improving the cycle performance of the lithium metal battery. Exemplarily, the concentration of the first lithium salt can be 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.3 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L or the range composed of any two of the above values.

[0072] In some embodiments, the first electrolyte further includes a first additive, and the first additive is configured to form a Cathode Electrolyte Interphase (CEI) film on the surface of the positive electrode sheet, which can play a good protective role for the positive active material in the positive electrode sheet, improve the structural stability of the positive active material, and thus improve the cycle performance of the lithium metal battery; moreover, the above first additive can also reduce the viscosity of the electrolyte, further improve the ionic conductivity of the first electrolyte, and is beneficial to further improving the kinetic performance of the lithium metal battery.

[0073] Exemplarily, the first additive may include at least one of lithium nitrate, lithium difluorophosphate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0074] Optionally, based on the total mass of the sulfone solvent and the dinitrile solvent, the mass content of the first additive is 0.5% to 10%; optionally 0.5% to 2.5%.

[0075] Exemplarily, the mass content of the first additive can be 0.5%, 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, 1.8%, 2.0%, 2.1%, 2.2%, 2.3%, 2.5%, 2.8%, 3.0%, 3.5%, 4.0%, 4.5%, 4.8%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10% or a range composed of any two of the above values.

[0076] [Second electrolyte solution]

[0077] The second electrolyte solution includes a second solvent, and the second solvent includes a chain monoether solvent. Optionally, the second solvent is a chain monoether solvent.

[0078] In some embodiments, the relative dielectric constant of the chain monoether solvent is 2.0 to 6.0; optionally 2.0 to 4.5. The above chain monoether solvent has weak molecular polarity and excellent electrochemical reduction stability, and the interfacial stability between it and the negative electrode sheet can be significantly improved, thereby improving the cycle stability of the lithium metal battery. And as the chain length of the chain monoether solvent increases (for example, the number of carbon atoms increases), the reduction stability of the chain monoether solvent on the negative electrode sheet side is enhanced, it is not easily decomposed, and the interfacial stability between it and the negative electrode sheet can be further improved.

[0079] Exemplarily, the relative dielectric constant of the chain monoether solvent can be 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8, 4.0, 4.2, 4.5, 4.8, 5.0, 5.5, 6.0 or a range composed of any two of the above values.

[0080] In some embodiments, the chain monoether solvent includes at least one of C2 to C10 chain monoether solvents; optionally C4 to C8 chain monoether solvents.

[0081] For example, the C2 to C10 chain monoether solvents include at least one of C2 chain monoether solvent, C3 chain monoether solvent, C4 chain monoether solvent, C5 chain monoether solvent, C6 chain monoether solvent, C7 chain monoether solvent, C8 chain monoether solvent, C9 chain monoether solvent, C10 chain monoether solvent.

[0082] In some embodiments, the C2 to C10 linear monoether solvents include at least one of diethyl ether, dipropyl ether, dibutyl ether, methyl propyl ether, and methyl butyl ether. Further optionally, the C4 to C8 linear monoether solvents may include at least one of dipropyl ether, dibutyl ether, and methyl butyl ether.

[0083] In some embodiments, the second electrolyte further includes a second lithium salt, and the second lithium salt includes at least one of lithium hexafluorophosphate (LiPF 6 )、lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and lithium difluoro(oxalato)borate (LiDFOB). The above-mentioned second lithium salt has strong lithium ion dissociation ability and excellent electrochemical stability in the second solvent.

[0084] Optionally, the second lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0085] Optionally, the first lithium salt and the second lithium salt can be the same lithium salt, which is beneficial to the migration of lithium ions.

[0086] In some embodiments, the concentration of the second lithium salt is 0.5 mol / L to 3.0 mol / L; it can be optionally 0.5 mol / L to 1.2 mol / L. When the concentration of the second lithium salt is within the above range, it can improve the ionic conductivity of the second electrolyte and the wettability of the negative electrode sheet, which is beneficial to improving the migration rate of lithium ions, improving the kinetic performance of the lithium metal battery and reducing the polarization degree, thereby further improving the cycle performance of the lithium metal battery. Exemplarily, the concentration of the second lithium salt can be 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.3 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L or the range composed of any two of the above values.

[0087] In some embodiments, the second electrolyte further includes a second additive, and the second additive is configured to form a solid electrolyte interphase (SEI) film on the surface of the negative electrode sheet, which can play a good protective role for the negative active material in the negative electrode sheet, improve the structural stability of the negative active material, and thus improve the cycle performance of the lithium metal battery; moreover, the above-mentioned second additive can further improve the ionic conductivity of the second electrolyte, which is beneficial to further improving the kinetic performance of the lithium metal battery.

[0088] Exemplarily, the second additive may include at least one of lithium nitrate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,3-dioxolane, dimethoxymethane, and dimethoxyethane.

[0089] Optionally, based on the total mass of the chain monoether solvent, the mass content of the second additive is 0.5% to 10%; optionally 3% to 10%.

[0090] Exemplarily, the mass content of the second additive may be 0.5%, 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, 1.8%, 2.0%, 2.1%, 2.2%, 2.3%, 2.5%, 2.8%, 3.0%, 3.5%, 4.0%, 4.5%, 4.8%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10% or a range composed of any two of the above values.

[0091] Lithium metal battery

[0092] In a second aspect, the embodiments of the present application also provide a lithium metal battery.

[0093] A lithium metal battery, also known as a rechargeable battery or a storage battery, refers to a battery that can be activated by charging after discharging. Usually, a lithium metal battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time allows active ions to pass through.

[0094] In some embodiments, the lithium metal battery includes the electrolyte of any embodiment of the first aspect of the embodiments of the present application. Thus, the lithium metal battery of the embodiments of the present application can effectively improve the cycling performance of the lithium metal battery.

[0095] [Negative electrode plate]

[0096] In some embodiments, the lithium metal battery further includes a negative electrode plate, and the negative electrode plate may be a lithium metal negative electrode.

[0097] In some embodiments, the lithium metal negative electrode may include a negative electrode current collector. During the charging process of the lithium metal battery, lithium ions can be deposited on the surface of the negative electrode current collector to form a lithium metal layer; during the discharging process of the lithium metal battery, the lithium metal layer loses electrons to form lithium ions, which migrate to the positive electrode active material.

[0098] The negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0099] The lithium metal negative electrode does not exclude additional functional layers. For example, in some embodiments, the lithium metal negative electrode of the embodiment of the present application further includes a conductive layer (for example, composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0100] Optionally, the lithium metal negative electrode can further include a conductive layer disposed on at least one side of the negative electrode current collector, and the conductive layer includes a negative electrode conductive agent. As an example, the negative electrode conductive agent can include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0101] Further optionally, the conductive layer can further include a negative electrode binder. As an example, the negative electrode binder can include styrene-butadiene rubber SBR, water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, at least one of polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS, polyacrylamide PAM, polyvinyl alcohol PVA, sodium alginate SA, and carboxymethyl chitosan CMCS).

[0102] In some other embodiments, the lithium metal negative electrode can include a negative electrode current collector and a lithium metal layer disposed on at least one side of the negative electrode current collector. For example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the lithium metal layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0103] The material of the negative electrode current collector is as described above and will not be elaborated here.

[0104] The lithium metal negative electrode does not exclude additional functional layers. For example, in some embodiments, the lithium metal negative electrode of the embodiment of the present application further includes a conductive layer (for example, composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0105] Optionally, the lithium metal anode may further include a conductive layer disposed between the anode current collector and the lithium metal layer. The conductive layer includes an anode conductive agent, and the material of the anode conductive agent is as described above and will not be elaborated here. Further optionally, the conductive layer may further include an anode binder, and the material of the anode binder is as described above and will not be elaborated here.

[0106] [Positive electrode sheet]

[0107] In some embodiments, the lithium metal battery further includes a positive electrode plate, which includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector. The positive electrode film layer includes a positive electrode active material.

[0108] The positive electrode active material may include, but is not limited to, at least one of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds; examples of the lithium-containing transition metal oxides may include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0109] Optionally, the positive electrode active material may include a lithium-containing transition metal oxide. The above positive electrode active material is more resistant to high voltage, which is beneficial to improving the energy density of the lithium metal battery; moreover, when the above positive electrode active material is used in combination with the above electrolyte, the structural stability of the positive electrode active material is higher, which is beneficial to improving the cycle performance of the lithium metal battery.

[0110] In some embodiments, in order to further improve the energy density of the lithium metal battery, the positive electrode active material for the lithium metal battery may include a lithium-containing transition metal oxide with the general formula Li a Ni b Co c M d O e A f and at least one of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes at least one of N, F, S, and Cl.

[0111] As an example, the positive electrode active material for the lithium metal battery may include LiCoO 2 、LiNiO 2 、LiMnO2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), LiNi 0.96 Co 0.02 Mn 0.02 O 2 (Ni96), LiNi 0.80 Co 0.15 Al 0.05 O 2 , and at least one of the lithium-rich manganese-based materials (xLi 2 MnO 3 ·(1 - x)LiMO 2 , where M is a transition metal element).

[0112] Optionally, 0.8 ≤ b ≤ 1, 0 ≤ c ≤ 0.2, 0 ≤ d ≤ 0.1, and M includes at least one of Mn and Al.

[0113] Exemplarily, a can be 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.1, 1.2 or a range composed of any two of the above values.

[0114] Exemplarily, b can be 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range composed of any two of the above values.

[0115] Exemplarily, c can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range composed of any two of the above values.

[0116] Exemplarily, d can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range composed of any two of the above values.

[0117] In the embodiments of the present application, the modified compounds of the above-mentioned cathode active materials may be doping modification and / or surface coating modification of the cathode active materials.

[0118] During the charge and discharge process of a lithium metal battery, the insertion and extraction and consumption of active ions such as Li will occur. The molar content of Li is different when the lithium metal battery is discharged to different states. In the listing of the cathode active materials in the embodiments of the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li may change.

[0119] In the listing of the cathode active materials in the embodiments of the present application, the molar content of oxygen O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will show fluctuations.

[0120] In some embodiments, based on the total mass of the cathode film layer, the mass percentage content of the cathode active material may be 85 wt% to 95 wt%. The cathode active material in this content range can endow the cathode electrode with higher capacity and better cycle performance.

[0121] In some embodiments, the cathode film layer may further optionally include a cathode conductive agent. The embodiments of the present application do not particularly limit the type of the cathode conductive agent. As an example, the cathode conductive agent includes at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, based on the total mass of the cathode film layer, the mass percentage content of the cathode conductive agent is ≤5%.

[0122] In some embodiments, the cathode film layer may further optionally include a cathode binder. The embodiments of the present application do not particularly limit the type of the cathode binder. As an example, the cathode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. In some embodiments, based on the total mass of the cathode film layer, the mass percentage content of the cathode binder is ≤5%.

[0123] In some embodiments, the positive current collector can be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer can include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0124] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0125] [Separator Film]

[0126] In some embodiments, the lithium metal battery further includes a separator film.

[0127] In some embodiments, the lithium metal battery also includes a separator film. The type of the separator film in the embodiments of the present application is not particularly limited, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0128] In some embodiments, the material of the separator film can include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The separator film can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation. The separator film of the above materials has better compatibility with the chain monoether solvent, and when injecting the electrolyte, the separator film can be disposed in the second electrolyte containing the chain monoether solvent.

[0129] In some embodiments, the positive electrode sheet, the separator film, and the negative electrode sheet can be made into an electrode assembly by a winding process and / or a stacking process.

[0130] In some embodiments, the lithium metal battery can include an outer package. The outer package can be used to encapsulate the above electrode assembly and electrolyte.

[0131] In some embodiments, the outer package of the lithium metal battery can be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the lithium metal battery can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0132] There is no particular limitation on the shape of the lithium metal battery in the embodiments of the present application, and it can be cylindrical, square, or any other shape. As Figure 1 shown is a lithium metal battery 5 with a square structure as an example.

[0133] In some embodiments, as Figure 2 shown, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 52 through a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the lithium metal battery 5 can be one or more, which can be adjusted according to requirements.

[0134] The preparation method of the lithium metal battery in the embodiments of the present application is well-known. In some embodiments, the positive electrode plate, the separator, the negative electrode plate, and the electrolyte can be assembled to form a lithium metal battery. As an example, the positive electrode plate, the separator, and the negative electrode plate can form an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in the outer package, dried, and then the electrolyte is injected, and after processes such as vacuum packaging, standing, formation, and shaping, a lithium metal battery is obtained.

[0135] In some embodiments of the embodiments of the present application, the lithium metal battery according to the embodiments of the present application can be assembled into a battery module, and the number of lithium metal batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0136] Figure 3 shown is a schematic diagram of a battery module 4 as an example. As Figure 3 shown, in the battery module 4, multiple lithium metal batteries 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 way. Further, the multiple lithium metal batteries 5 can be fixed by fasteners.

[0137] Optionally, the battery module 4 can further include a housing having a receiving space, and multiple lithium metal batteries 5 are received in the receiving space.

[0138] In some embodiments, the above battery modules can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack. The lithium metal battery, the battery module, and the battery pack can all be taken as examples of a battery.

[0139] Figure 4 And Figure 5 are schematic diagrams of a battery pack 1 as an example. As Figure 4 and Figure 5 shown, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0140] Power consumption device

[0141] In a second aspect, embodiments of the present application provide an electrical device. The electrical device includes at least one of the lithium metal battery, the battery module, or the battery pack according to the embodiments of the present application. The lithium metal battery, the battery module, or the battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0142] The electrical device can select the lithium metal battery, the battery module, or the battery pack according to its usage requirements.

[0143] Figure 6 are schematic diagrams of an electrical device 6 as an example. The electrical device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 6 for high power and high energy density, a battery pack or a battery module can be adopted.

[0144] Another example of the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. This electrical device usually requires being thin and light, and a lithium metal battery can be adopted as the power source.

[0145] Example

[0146] The following examples describe more specifically the content disclosed in the embodiments of the present application. These examples are for illustrative purposes only, as various modifications and variations within the scope of the content disclosed in the embodiments of the present application are obvious 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 can be used directly without further treatment, and all instruments used in the examples are commercially available.

[0147] Example 1 Preparation of Lithium Metal Battery

[0148] 1. Preparation of Positive Electrode

[0149] The positive electrode includes a positive current collector and a positive electrode film layer. The positive current collector is aluminum foil, and the positive electrode film layer is formed by uniformly coating a positive electrode paste (with N-methylpyrrolidone NMP as the solvent) on the surface of the aluminum foil of the positive current collector, followed by drying and cold pressing. The positive electrode film layer includes a positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 98:1:1.

[0150] The positive electrode active material includes a compound with the molecular formula LiNi 0.8 Co 0.10 Mn 0.10 O 2 (NCM811).

[0151] 2. Preparation of Lithium Metal Negative Electrode

[0152] The lithium metal negative electrode includes a negative current collector and negative electrode film layers provided on both sides of the negative current collector. The negative current collector is copper foil, and the negative electrode film layer is a lithium metal sheet.

[0153] 3. Separator

[0154] The separator is a polyethylene film layer.

[0155] 4. Preparation of Electrolyte

[0156] The electrolyte includes a first electrolyte and a second electrolyte, and the specific components of the electrolyte are shown in Table 1.

[0157] 5. Preparation of Lithium Metal Battery

[0158] Stack the above positive electrode, separator, and lithium metal negative electrode in sequence, with the separator placed between the positive electrode and the lithium metal negative electrode to play a separating role, obtaining an electrode assembly; place the electrode assembly in an outer packaging case, inject the electrolyte after drying, and go through processes such as vacuum packaging, standing, forming, and shaping to obtain a laminated lithium metal battery, where the separator is disposed in the first electrolyte.

[0159] Comparative Example 1

[0160] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Comparative Example 1, the composition of the electrolyte was adjusted. The electrolyte included an organic solvent and a lithium salt. The organic solvent was 3-methylsulfolane, and the lithium salt was 1 mol / L lithium bis(fluorosulfonyl)imide LiFSI.

[0161] Comparative Example 2

[0162] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Comparative Example 2, the composition of the electrolyte was adjusted. The electrolyte included an organic solvent and a lithium salt. The organic solvent was dipropyl ether, and the lithium salt was 1 mol / L lithium bis(fluorosulfonyl)imide LiFSI.

[0163] Comparative Example 3

[0164] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Comparative Example 3, the composition of the electrolyte was adjusted. The electrolyte included an organic solvent, a lithium salt, and an additive. The organic solvent was dipropyl ether, the lithium salt was 1 mol / L lithium bis(fluorosulfonyl)imide LiFSI, and the additive was lithium nitrate. The mass content of lithium nitrate relative to the total mass of the organic solvent was 2%.

[0165] Comparative Example 4

[0166] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Comparative Example 4, the composition of the electrolyte was adjusted. The electrolyte included an organic solvent and a lithium salt. The organic solvent was 3-methylsulfolane and dipropyl ether, and the lithium salt was 1 mol / L lithium bis(fluorosulfonyl)imide LiFSI.

[0167] Examples 2 and 3

[0168] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Examples 2 and 3, the composition of the first solvent in the first electrolyte was adjusted.

[0169] Examples 4 to 6

[0170] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Examples 4 to 6, the composition of the second solvent in the second electrolyte was adjusted.

[0171] Examples 7 to 9

[0172] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Examples 7 to 9, the concentration of the first lithium salt in the first electrolyte was adjusted.

[0173] Example 10

[0174] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Example 10, the types of the first lithium salt in the first electrolyte and the second lithium salt in the second electrolyte were adjusted.

[0175] Example 11

[0176] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Example 11, the first electrolyte was adjusted and a first additive was additionally added.

[0177] Example 12

[0178] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 11, in Example 12, the mass content of the second additive in the second electrolyte was adjusted.

[0179] Example 13

[0180] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Example 13, the first electrolyte was adjusted and a first additive was additionally added, and the types and mass content of the second additive in the second electrolyte were adjusted.

[0181] Examples 14 and 15

[0182] A lithium metal battery was prepared using a method similar to that of Example 1. Different from Example 1, in Examples 14 and 15, the volume ratio of the first solvent in the first electrolyte to the second solvent in the electrolyte was adjusted.

[0183] The relevant parameters of the examples and comparative examples are shown in Table 1 below.

[0184] Performance test

[0185] 1. Performance test of the lithium metal battery

[0186] Take the prepared lithium metal battery above and perform charge-discharge cycling at a rate of 0.1C (i.e., 7 mA) in an environment of 25°C. The charge-discharge voltage window is set to 2.8 - 4.5V. When the discharge capacity decays to 80% of the discharge capacity in the first cycle, it is considered that the life of the lithium metal battery terminates, and the number of charge-discharge cycles of the lithium metal battery is recorded.

[0187] Test result

[0188] The test results are shown in Table 1.

[0189] Table 1

[0190]

[0191] In Table 1, "-" indicates that such a substance is not added, or this data is meaningless.

[0192] "C 5 H 10 O 2 S" represents 3-methylsulfolane.

[0193] "C 5 H 4 F 8 O" represents 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0194] "DPE" represents dipropyl ether.

[0195] ∈ r1 represents the relative dielectric constant of the first solvent, ∈ r2 represents the relative dielectric constant of the second solvent, and L represents the volume ratio of the first solvent to the second solvent.

[0196] As can be seen from Table 1, in Comparative Examples 1 to 3, the electrolytes use only the first solvent or the second solvent as the organic solvent. Due to their poor stability on the positive electrode sheet or the negative electrode sheet side, the cycling performance of the lithium metal battery is relatively poor, and a good cycle life cannot be obtained. Although the electrolyte in Comparative Example 4 contains both the first solvent and the second solvent, they are in the same system and cannot modify the battery well.

[0197] Compared with Comparative Examples 1 to 3, the electrolyte in the examples is a two-phase system. One phase is the first electrolyte containing a sulfone solvent and / or a dinitrile solvent, and the other phase is the second electrolyte containing a linear monoether solvent. The stability of the first electrolyte at the interface with the positive electrode sheet is relatively high, and the stability of the second electrolyte at the interface with the negative electrode sheet is relatively high, which is beneficial to improving the cycling performance of the lithium metal battery.

[0198] In Examples 1 to 3, by adjusting the materials of the sulfone solvent and the dinitrile solvent, the wettability of the first electrolyte on the positive electrode sheet can be optimized. For example, 3-methylsulfolane with a relatively low melting point is selected, which has a small viscosity and is beneficial to improving the wettability on the positive electrode sheet and enhancing the cycle life.

[0199] In Examples 1, 4 to 6, by adjusting the materials of the linear monoether solvent, the interfacial stability between the second electrolyte and the lithium metal negative electrode can be optimized. For example, a linear monoether solvent with a longer chain is selected, which has higher reduction stability on the lithium metal negative electrode side and can further enhance the interfacial stability between the second electrolyte and the lithium metal negative electrode.

[0200] In Examples 7 to 10, by adjusting the concentration and material of the lithium salt, the cycle life of the lithium metal battery can be further improved; especially when the first electrolyte and the second electrolyte use the same lithium salt, it is beneficial to the rapid transmission of lithium ions and improves the kinetic performance of the lithium metal battery; the lithium salt can be selected as lithium bis(fluorosulfonyl)imide (LiFSI).

[0201] In Examples 11 to 13, by adjusting the material and mass content of the additive in the first electrolyte, the protective performance of the positive electrode sheet can be improved, and the interfacial stability between the positive electrode sheet and the first electrolyte can be enhanced; by adjusting the material and mass content of the additive in the second electrolyte, the protective performance of the negative electrode sheet can be improved, and the interfacial stability between the negative electrode sheet and the second electrolyte can be enhanced, which is beneficial to further improving the cycle performance of the lithium metal battery.

[0202] In Examples 1, 14 and 15, by adjusting the volume ratio of the first electrolyte and the second electrolyte, the chemical potential equilibrium can be quickly achieved during the migration of lithium ions in the two-phase system, the migration barrier of lithium ions can be reduced, the ionic conductivity of the electrolyte can be increased, and the kinetic performance of the battery can be improved.

[0203] In summary, in the embodiments of the present application, by using sulfone solvents and / or sulfoxide solvents with intrinsic phase separation and excellent oxidation resistance as the solvents on the positive electrode side, and chain monoether solvents with excellent reduction resistance as the solvents on the negative electrode side, the electrochemical cycling window of the electrolyte can be widened to more than 5V. By optimizing the type, concentration of the lithium salt and the composition of the additive, the ionic conductivity, wettability of the electrode sheet and interfacial film-forming ability of the electrolyte can be further improved, so as to realize the matching use and stable cycling of the high-voltage positive electrode and the lithium metal negative electrode. At room temperature and under the condition of a 4.5V charging cut-off, the cycle life of the lithium metal battery can reach 350 cycles.

[0204] Although the illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations of the present application, and the embodiments can be changed, substituted and modified without departing from the spirit, principle and scope of the present application.

Claims

1. An electrolyte for a lithium metal battery, comprising a first electrolyte and a second electrolyte. The first electrolyte comprises a first solvent, and the first solvent comprises at least one of a sulfone solvent and a dinitrile solvent. The second electrolyte comprises a chain monoether solvent, and the difference between the relative dielectric constant of the first solvent and the relative dielectric constant of the chain monoether solvent is ≥25.

2. The electrolyte for a lithium metal battery according to claim 1, wherein, the relative dielectric constant of the sulfone solvent is 25 to 60; optionally 28 to 50; optionally, the sulfone solvent comprises at least one of a C4 to C6 cyclic sulfone and a C2 to C8 chain sulfone; further optionally, the C4 to C6 cyclic sulfone comprises at least one of sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane; further optionally, the C2 to C8 chain sulfone comprises at least one of dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, methyl isopropyl sulfone, dipropyl sulfone, and dibutyl sulfone.

3. The electrolyte for a lithium metal battery according to claim 1 or 2, wherein, the relative dielectric constant of the dinitrile solvent is 50 to 80; optionally 50 to 60; optionally, the dinitrile solvent comprises at least one of C3 to C6 chain dinitriles; further optionally, the C3 to C6 chain dinitrile comprises at least one of malononitrile, succinonitrile, glutaronitrile, and adiponitrile.

4. The electrolyte for a lithium metal battery according to any one of claims 1 to 3, wherein, the relative dielectric constant of the chain monoether solvent is 2.0 to 6.0; optionally 2.0 to 4.5; optionally, the chain monoether solvent comprises a C2 to C10 chain monoether solvent; optionally a C4 to C8 chain monoether solvent; further optionally, the C2 to C10 chain monoether solvent comprises at least one of diethyl ether, dipropyl ether, dibutyl ether, methyl propyl ether, and methyl butyl ether; further optionally, the C2 to C10 chain monoether solvent comprises at least one of dipropyl ether, dibutyl ether, and methyl butyl ether.

5. The electrolyte for a lithium metal battery according to any one of claims 1 to 4, wherein, the total volume of the first solvent in the first electrolyte is A mL, and the volume of the chain monoether solvent in the second electrolyte is B mL, where A / B is 0.5 to 2; optionally 0.8 to 1.

2.

6. The electrolyte for a lithium metal battery according to any one of claims 1 to 5, wherein, the first electrolyte further comprises a first additive, and the first additive comprises at least one of lithium nitrate, lithium difluorophosphate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; optionally, based on the total mass of the first solvent, the mass content of the first additive is 0.5% to 10%; optionally 0.5% to 2.5%.

7. The electrolyte for a lithium metal battery according to any one of claims 1 to 6, wherein, The second electrolyte further includes a second additive, and the second additive may include at least one of lithium nitrate, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, 1,3-dioxolane, dimethoxymethane, and dimethoxyethane; Optionally, Based on the total mass of the chain monoether solvent, the mass content of the second additive is 0.5% to 10%; it may be optionally 3% to 10%.

8. The electrolyte for a lithium metal battery according to any one of claims 1 to 7, wherein, The first electrolyte further includes a first lithium salt, and the first lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, and lithium difluoro(oxalato)borate; Optionally, The first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate; Further optionally, The concentration of the first lithium salt is 0.5 mol / L to 3.0 mol / L; it may be optionally 0.5 mol / L to 2.0 mol / L.

9. The electrolyte for a lithium metal battery according to any one of claims 1 to 8, wherein, The second electrolyte further includes a second lithium salt, and the second lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, and lithium difluoro(oxalato)borate; Optionally, The second lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonylimide; Further optionally, The concentration of the second lithium salt is 0.5 mol / L to 3.0 mol / L; it may be optionally 0.5 mol / L to 1.2 mol / L.

10. A lithium metal battery, comprising the electrolyte for a lithium metal battery according to any one of claims 1 to 9.

11. The lithium metal battery according to claim 10, further comprising a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, the positive electrode film layer includes a positive electrode active material, and the positive electrode active material includes a lithium-containing transition metal oxide; Optionally, the lithium-containing transition metal oxide includes at least one of compounds with the general formula Li a Ni b Co c M d O e A f where 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M includes at least one of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A includes at least one of N, F, S, and Cl.

12. An electrical device, comprising the lithium metal battery according to claim 10 or 11.

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